Enhanced Piezoelectric Strain Sensitivity in Electrospun PVDF/MWCNT Nanofibers via Moderate Mechanical Stretching and β-Phase Orientation

Enhanced Piezoelectric Strain Sensitivity in Electrospun PVDF/MWCNT Nanofibers via Moderate Mechanical Stretching and β-Phase Orientation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Enhanced Piezoelectric Strain Sensitivity in Electrospun PVDF/MWCNT Nanofibers via Moderate Mechanical Stretching and β-Phase Orientation Atiyeh Amirhosseini, Mahdi Nouri, Mostafa Jamshidi Avanaki This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8916823/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract Electrospun poly(vinylidene fluoride) (PVDF)–based nanofibrous composites have attracted considerable interest for flexible and wearable strain-sensing applications due to their intrinsic piezoelectricity, low density, and mechanical compliance. In this study, PVDF/multi-walled carbon nanotube (MWCNT) nanofibrous composites were fabricated via electrospinning to systematically investigate the combined effects of CNT loading and in-process mechanical stretching on morphology, crystalline structure evolution, mechanical properties, and piezoelectric strain sensitivity. MWCNT contents of 0.05, 0.2, and 0.5wt% were incorporated into PVDF solutions electrospun under fixed parameters, with nanofibers collected under random and mechanically stretched (using a rotating drum collector at 500 rpm) conditions. Structural and phase analyses (SEM, XRD, FT-IR) revealed that the synergistic action of jet stretching and CNT-induced nucleation significantly enhanced the content and dipole orientation of the electroactive β-phase, particularly at 0.05wt% CNT loading. Mechanical testing demonstrated that stretched nanofiber mats exhibited superior tensile strength and stability compared to random mats. Piezoelectric measurements under dynamic loading showed that the stretched PVDF/MWCNT nanofibers containing 0.05wt% CNT generated the highest output voltage (~ 4.9 mV) and strain sensitivity (1.84 mV·N⁻¹). These results demonstrate a clear processing–structure–property relationship and identify optimal electrospinning conditions for high-performance, flexible PVDF-based strain sensors. Electrospinning PVDF/MWCNT nanocomposites β-phase orientation Piezoelectric strain sensor Mechanical stretching Structure-property relationship Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1. Introduction The rapid expansion of flexible electronics, wearable technologies, and intelligent structural health monitoring systems has stimulated extensive research into polymer-based piezoelectric materials capable of converting mechanical stimuli into electrical signals [ 1 , 2 ]. Among these materials, polyvinylidene fluoride (PVDF) has emerged as one of the most promising piezoelectric polymers owing to its low density, mechanical flexibility, chemical resistance, and excellent electromechanical coupling [ 3 ]. These attributes make PVDF particularly attractive for pressure sensors, self-powered devices, and smart textile applications [ 4 , 5 ]. PVDF is a semi-crystalline polymer that can crystallize into several polymorphic phases, including α, β, γ, δ, and ε [ 3 ]. Among them, the β phase exhibits the highest polarity due to its all-trans molecular conformation and is therefore primarily responsible for the piezoelectric, ferroelectric, and pyroelectric properties of PVDF [ 6 , 7 ]. Recent studies on composite systems have further confirmed that the β-phase fraction directly governs the piezoelectric coefficient and strain sensitivity of PVDF-based sensors [ 1 , 6 , 8 ]. Consequently, the sensitivity and efficiency of PVDF-based sensors are strongly dependent on the β-phase fraction, making its enhancement a central objective in the design of high-performance piezoelectric materials [ 1 , 6 ]. Electrospinning has proven to be an effective and scalable technique for inducing and aligning the β-phase in PVDF nanofibers without the need for post-poling treatments [ 6 , 9 ]. The strong electric field, combined with elongational forces acting on the polymer jet, promotes molecular chain and dipole orientation along the fiber axis, leading to self-polarized nanofibrous structures [ 10 ]. This inherent control over morphology also yields fibers with high surface area, porosity, and breathability—attributes that are critical for integration into wearable and flexible sensing systems [ 4 , 5 ]. In addition to processing conditions, the mechanical stretching and orientation of nanofibers during collection plays a crucial role in determining the crystalline structure and piezoelectric response of electrospun PVDF [ 10 ]. The use of rotating collectors during electrospinning introduces controlled mechanical stretching, resulting in improved molecular orientation, reduced fiber diameter, and increased β-phase content compared to randomly collected fibers [ 10 , 11 ]. Several studies have demonstrated that this induced orientation through mechanical stretching significantly enhances both mechanical strength and piezoelectric sensitivity [ 11 ], although it is noted that excessively high rotation speeds may cause fiber breakage and structural defects [ 10 , 12 ]. The incorporation of carbon nanotubes (CNTs) into PVDF matrices provides another effective strategy for enhancing electromechanical performance. CNTs can act as nucleating agents that promote α-to-β phase transformation through strong interfacial interactions with PVDF chains [ 7 , 8 ], while simultaneously improving mechanical reinforcement and electrical conductivity when dispersed below the electrical percolation threshold [ 13 ]. Recent investigations have shown that optimized CNT loading in electrospun PVDF fibers enables enhanced strain sensitivity, stability under cyclic loading, and multifunctional sensing capabilities, including pressure, motion, and respiration detection [ 4 , 8 ]. Despite significant progress in electrospun PVDF-based piezoelectric materials [ 6 , 9 , 14 ], a systematic understanding of the combined effects of electrospinning-induced jet stretching, collector-imposed mechanical stretching, and carbon nanotube (CNT) loading on β-phase formation and strain-sensing performance remains incomplete. In particular, the interdependent roles of CNT-induced nucleation and electrospinning-induced chain orientation in governing the electromechanical response of PVDF nanofibers have not been fully clarified. The objective of this study is to elucidate the synergistic roles of electrospinning-induced mechanical stretching and molecular orientation and MWCNT incorporation in governing the morphology, crystalline phase evolution, mechanical properties, and strain-sensing performance of PVDF nanofibrous composites. By systematically varying CNT content (0–0.5wt%) and collector-induced mechanical stretching, this work clarifies the interplay between CNT-induced β-phase nucleation, stretching-induced molecular orientation, mechanical reinforcement, and their combined effect on piezoelectric strain sensitivity. Through comprehensive structural, mechanical, and piezoelectric characterization, the study seeks to identify optimal material compositions and processing parameters that maximize strain sensitivity while preserving mechanical flexibility and stability. This approach is designed to advance the development of efficient and scalable PVDF-based piezoelectric strain sensors. 2. Experimental 2.1. Materials Polyvinylidene fluoride (PVDF) powder (Kynar 761, Mw ≈ 520,000g·mol⁻¹), a semi-crystalline polymer with a melting temperature of 165–172°C, was used as the matrix material. Multi-walled carbon nanotubes (MWCNTs) with a purity above 98%, an outer diameter of 10–20nm, an average length of ~ 30µm, a specific surface area of 150 m²·g⁻¹, ~ 2% surface –COOH functionalization, and less than 1.5%wt ash content were employed as conductive fillers and nucleating agents. N, N-dimethyl formamide (DMF) and acetone (both from Merck, Germany) were used as solvents. Solution preparation involved precise weighing using analytical balances, magnetic stirring, and ultrasonic dispersion. 2.2. Preparation of PVDF/MWCNT Electrospinning Solutions To achieve uniform dispersion of carbon nanotubes and minimize agglomeration, the electrospinning solutions were prepared using a two-step mixing strategy, as recommended in previous studies on CNT composite processing [ 13 ] and applied in PVDF/MWCNT systems [ 8 ]. First, a neat PVDF solution was prepared by dissolving PVDF powder in a mixed solvent system consisting of acetone and DMF at a volume ratio of 4:6. The solution was placed on a hot plate equipped with a magnetic stirrer and heated to 50°C for 5minutes then at room temperature for 1h to obtain a homogeneous polymer solution. For the preparation of CNT-containing solutions, predetermined amounts of MWCNTs corresponding to weight fractions of 0.05, 0.2, and 0.5%wt relative to PVDF were accurately weighed and dispersed in acetone/DMF solvent mixture (4:6 v/v). MWCNT loading is reported as %wt relative to PVDF mass (MWCNT/PVDF × 100). To achieve homogeneous dispersion, the solution was placed in an ultrasonic bath for 40 minutes at 50°C. Subsequently, the CNT dispersion and PVDF solution were combined and magnetically stirred for 35min at room temperature to obtain stable and uniform PVDF/MWCNT electrospinning solutions. 2.3. Electrospinning Process and Nanofiber Fabrication Electrospinning was carried out using a syringe-based electrospinning system equipped with a high-voltage power supply and a rotating collector. The prepared solutions were loaded into a syringe fitted with a metallic needle and delivered at a constant flow rate of 1mL·h⁻¹. Electrospinning was performed with a needle-to-collector distance of 18cm. A voltage of 18–19kV was applied between the needle (positive electrode) and the collector (negative electrode), and electrospinning was performed for 4h under controlled environmental conditions (T: 25–26°C; RH: 60–65% for all samples). Partially aligned/oriented nanofibers were collected using a rotating drum collector operating at 500rpm to impart controlled mechanical stretching, while random mats were obtained by operating the same collector at a minimal speed, consistent with established techniques for inducing fiber orientation. [ 10 ]. The rotation of the collector at 500rpm was employed to impart controlled mechanical stretching to the polymer jet. This induced partial fiber alignment and promoted molecular chain orientation during solidification, while avoiding the excessive speeds that can lead to fiber breakage. This approach allows investigation of the effects of in-process tensile forces on fiber properties. For preliminary observation of fiber morphology, electrospinning was performed onto glass slides for 15min, and the samples were examined using an optical microscope. 3. Characterization Techniques 3.1. Morphological Analysis, Structural and Phase Characterization Surface morphology and diameter of the nanofibers prepared by electrospinning were evaluated using scanning electron microscopy (SEM). The dispersion and average diameter of the nanofibers were measured using ImageJ software. Then, statistical calculations and relevant graphs were made using Origin Project software. XRD test was used to measure the formation of β phase, and FT-IR spectroscopy was used to calculate and examine the amount of formation of the polar β phase. 3.2. Phase Identification and β-Phase Quantification by FT-IR The crystalline phases of PVDF in the prepared nanofibrous composites were analyzed using Fourier-transform infrared (FT-IR) spectroscopy, which is a widely used technique for distinguishing the electroactive β-phase from the non-polar α-phase of PVDF based on characteristic vibrational absorption bands. The electroactive β-phase was identified using the characteristic absorption band located at approximately 840cm⁻¹, which is attributed to CF₂ stretching vibrations associated with the all-trans (TTTT) molecular conformation of PVDF. The α-phase contribution was identified using the absorption band at approximately 763cm⁻¹, corresponding to CF₂ bending and skeletal vibrations of the trans–gauche–trans–gauche′ (TGTG′) conformation [ 6 , 1 , 3 ]. This established spectroscopic method has been widely used for phase quantification in PVDF and its nanocomposites [ 6 ]. These peaks were selected because they are well separated, minimally affected by peak overlap, and are commonly used in the literature for semi-quantitative phase analysis of PVDF. All FT-IR spectra were baseline-corrected in the range of 700–900cm⁻¹ prior to analysis. The areas under the absorption peaks at ~ 763cm⁻¹ and ~ 840cm⁻¹ were calculated by numerical integration using identical integration limits for all samples. Peak area analysis was used instead of peak height measurement to reduce the influence of noise, peak broadening, and minor spectral shifts caused by CNT incorporation or processing variations. The relative β-phase fraction (F β ) was estimated using the following relationship [ 6 ]: F β = A β / (K β /K α * A α + A β ) (1) where A α and A β are the integrated absorbances of the α-phase (763cm⁻¹) and β-phase (840cm⁻¹) bands, respectively, and K α (6.1 × 10⁴ cm² mol⁻¹) and K β (7.7 × 10⁴ cm² mol⁻¹) are the absorption coefficients at the respective wavenumbers. 3.3. Mechanical Characterization of composite nanofibers To perform tensile strength testing, samples were stretched between two jaws using an Instron machine, with a stretching speed of 5mm/min and a working distance of 20mm between the two jaws. To place the nanofibers between the two jaws of the machine, paper frames of 40*40 mm 2 were prepared, and 30*5 mm 2 samples were mounted and secured over a square cut in the middle of the frame using a thin layer of adhesive. The raw force–elongation data from the Instron universal testing machines were processed to calculate the corresponding engineering stress and strain. These values were used to determine the tensile strength and to generate the stress–strain curves. 3.4. Piezoelectric and Strain-Sensing Measurements 3.4.1. Experimental Setup for Dynamic Piezoelectric Testing A custom-built cyclic compression apparatus was used to apply controlled dynamic force and simultaneously measure the piezoelectric voltage output (Fig. 1 ). The system consists of a DC motor coupled to an eccentric cam. The rotation of the cam converts the motor's rotary motion into a sinusoidal vertical displacement, which is transmitted through a rigid plunger to apply compressive force to the sample. The electrospun nanofibrous mat (1 × 1 cm²) was sandwiched between two aluminum foil electrodes (0.01 mm thickness) and placed on a flat, rigid base. A calibrated piezoelectric load cell was positioned between the base and the lower electrode to measure the applied force in real time. The DC motor's speed was regulated to achieve a consistent loading frequency of 5 Hz. The eccentricity of the cam was adjusted to produce a peak compressive force of 2.65 N—a magnitude chosen to represent moderate, application-relevant stress while ensuring a clear signal output. This target force was verified in real-time by the load cell, ensuring consistent stimulation across all samples. The open-circuit voltage generated by the sample was acquired using a high-impedance digital oscilloscope (GDS-1102, GW-Instek). The voltage signal from the sample and the force signal from the load cell were recorded synchronously, enabling direct correlation between mechanical input and electrical output. 3.4.2. Data Analysis and Sensitivity Evaluation The voltage–time and force–time signals were recorded synchronously by the oscilloscope. For each sample, testing was repeated for at least three loading cycles under stable conditions (n ≥ 3). The peak output voltage (V out​ ) was extracted as the absolute maximum of the steady-state voltage signal at the driving frequency (5 Hz). The peak force (F), corresponding to the timing of V out​ , was recorded simultaneously from the load cell. The piezoelectric strain sensitivity ( S ) was calculated as S=V out​ /F. Mean values and standard deviations of V out​ and S were derived from the repeated measurements for each sample. 4. Results and Discussion 4.1. Optimization of PVDF Concentration Nanofibrous samples prepared from different PVDF/MWCNT compositions were labelled according to their formulation and processing conditions. Solutions with concentrations of 12%, 15%, 18% and 20% by weight of PVDF with the same process settings were selected for electrospinning with random orientation. In the solution containing 20% by weight of PVDF, the high concentration increased the viscosity and gelation of the solution, its coagulation at the needle tip, lack of movement towards the collector, and consequently disrupted the electrospinning process, and no nanofibers were formed. In Fig. 2 , SEM images of the concentrations of 12%, 15% and 18% by weight are given. Electrospinning of the 12% by weight solution was accompanied by high spattering during the electrospinning process and, as shown in Fig. 2 , bead formation was observed in some samples. By examining the SEM images and calculating the average diameter of the nanofibers of each group, the average diameters were 406.53, 538.20, and 870.76 nm for the 12%, 15% and 18%wt samples, respectively. According to the previous studies, among the 15% and 18%wt concentrations that consisted of more uniform fibers and very little beads, the higher concentration (18%wt) was selected as the selected concentration to achieve nanofibers with a more uniform morphology and structure, for the preparation of all subsequent samples. 4.2. Effect of Electrospinning and CNT Content on Nanofiber Morphology The effect of carbon nanotube (CNT) loading and collector type on the morphology and diameter distribution of electrospun PVDF/MWCNT nanofibers was systematically investigated using SEM analysis. Representative SEM images and corresponding diameter frequency distributions for randomly collected nanofibers are shown in Fig. 3 , while Fig. 4 and Table 1 present the results for nanofibers subjected to mechanical stretching using a rotating drum collector. Table 1 Effect of MWCNT loading and collection condition on the average diameter of electrospun PVDF/MWCNT nanofibers Sample Code Collector Speed (rpm) PVDF (%wt) MWCNT (%wt) Mean Diameter (nm) Std. Deviation (nm) Diameter Range (nm) T1-R-0% 0 12 0 406.53 133.87 250–350 T2-R-0% 0 15 0 538.20 178.44 450–550 1-R- 0% 0 18 0 870.76 165.50 700–900 2-R-0.05% 0 18 0.05 1087.29 222.59 1000–1400 3-R-0.2% 0 18 0.20 1219.68 245.83 1000–1400 4-R-0.5% 0 18 0.50 973.60 245.62 800–1100 5-A-0% 500 18 0 503.20 152.01 350–600 6-A-0.05% 500 18 0.05 397.47 96.81 300–600 7-A-0.2% 500 18 0.20 607.26 161.96 400–650 8-A-0.5% 500 18 0.50 487.83 123.94 400–600 For pure PVDF nanofibers prepared with a random collector (sample 1-R-0%), the fibers exhibited a broad diameter distribution ranging from approximately 344 to 1304 nm, with an average diameter of 876.8 ± 165.5 nm and the highest frequency in the range of 700–1100 nm (Fig. 3 a). Upon incorporation of 0.05%wt MWCNT (sample 2-R-0.05%), denser fibrous regions were observed (Fig. 3 b), indicating improved spinnability; however, the average diameter increased to 1087.3 ± 222.6 nm. This increase is attributed to the rise in solution viscosity caused by CNT addition [ 13 ] under a constant applied voltage, consistent with previous reports on CNT-filled PVDF systems [ 7 , 8 ] and general nanocomposite processing [ 1 ]. Further increasing the CNT content to 0.2%wt (sample 3-R-0.2%) resulted in the largest average diameter (1219.7 ± 245.8 nm) and a wide diameter range (Fig. 3 c), suggesting that excessive viscosity and polymer chain entanglement hindered effective jet stretching. In contrast, at 0.5%wt CNT loading (sample 4-R-0.5%), the average diameter decreased markedly to 605.0 ± 62.2 nm (Fig. 3 d). This reduction is attributed to the increased electrical conductivity of the solution, which enhanced the electrostatic stretching force acting on the polymer jet, overcoming viscous effects and producing finer fibers [ 6 , 14 ]. This mechanism is in agreement with established electrospinning theories governing jet dynamics and fiber formation for piezoelectric polymers [ 6 , 10 ] and is consistent with observations in composite systems [ 1 ]. A pronounced reduction in fiber diameter and dispersion was observed when a rotating collector was employed. Pure PVDF fibers subjected to mechanical stretching during collection exhibited a much smaller average diameter (≈ 503 nm) and narrower distribution compared to randomly collected fibers (Fig. 4 a). This trend is further enhanced by CNT incorporation. The mechanically stretched sample containing 0.05%wt MWCNT showed the smallest average diameter among all samples (≈ 397 nm) with the highest uniformity and a dominant diameter range of 400–600 nm (Fig. 4 b). The reduction in fiber diameter results from a synergistic electro-mechanical process. First, the incorporation of conductive CNTs increases the solution's charge-carrying capacity, enhancing the electrostatic stretching force exerted on the polymer jet during electrospinning [ 15 ]. Second, the tangential force imposed by the high-speed rotating collector applies an additional longitudinal mechanical stress, further elongating the jet before solidification [ 10 ]. The combined action of this enhanced electrostatic pull and direct mechanical drawing overcomes the solution's viscous resistance, leading to significant jet attenuation and the production of finer, oriented fibers. This interplay between electrical and mechanical parameters is a cornerstone of controlled electrospinning [ 12 ] and is an established strategy for fabricating high-performance, oriented piezoelectric nanofibers [ 11 ]. At higher CNT contents (0.2 and 0.5%wt, samples 7-A-0.2% and 8-A-0.5%), the average diameter increased slightly compared to sample 6-A-0.05% (Fig. 4 c and d), which can be attributed to increased solution viscosity and partial CNT agglomeration. Nevertheless, these mechanically stretched fibers remained significantly thinner and more uniform than their randomly collected counterparts, highlighting the dominant role of collector-induced tensile force in controlling fiber morphology. Overall, the results demonstrate that nanofiber diameter and uniformity are governed by a balance between solution viscosity, electrical conductivity, and mechanical stretching during electrospinning [ 6 , 12 ], consistent with processing principles for PVDF composites [ 1 ]. An optimal CNT content of 0.05%wt, combined with mechanical stretching during collection, yields the most uniform and finest nanofibers. This outcome is consistent with reports linking refined fiber morphology to improved flexibility and enhanced piezoelectric strain sensitivity in PVDF-based nanofibrous sensors [ 4 , 11 ]. 4.3. β-Phase Formation Induced by Electrospinning and CNT Nucleation (FT-IR and XRD correlation) The crystalline structure and β-phase evolution of the electrospun PVDF/MWCNT nanofibrous composites were investigated using X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. As reported in previous studies, the electroactive β phase of PVDF is characterized by diffraction peaks appearing at 2θ ≈ 20–21°, corresponding to the (110)/(200) planes of the β crystalline phase [ 6 , 8 , 14 ], which is a standard identification method in the literature [ 1 , 3 ]. In the present study, all samples exhibited a dominant diffraction peak in this region, as shown in Fig. 5 , confirming the formation of the β phase in electrospun nanofibers. Although the presence of a single dominant peak limited phase identification, variations in peak intensity provided valuable insight into changes in crystallinity and molecular orientation. According to the XRD intensity data summarized in Table 2 and illustrated in Fig. 6 , samples containing 0.05%wt MWCNT (samples 2-R-0.05% and 6-A-0.05%) exhibited significantly higher peak intensities compared to other compositions. In particular, the mechanically stretched sample with 0.05%wt MWCNT showed the highest intensity among all samples, indicating enhanced crystalline ordering and β-phase development. This observation is consistent with earlier reports that electrospinning-induced jet stretching and collector-induced tensile forces promote molecular chain alignment and dipole orientation along the fiber axis [ 10 , 11 ]. The observed β-phase enhancement at 0.05%wt MWCNT is attributed to the electrostatic interaction between the electronegative fluorine atoms in PVDF's CF₂ dipoles and the π-electron cloud of the CNTs, which templates the all-trans (TTTT) chain conformation and is consistent with self-polarization mechanisms reported for electrospun PVDF under strong elongational and electric fields [ 6 , 9 , 14 ]. Table 2 XRD peak intensity of electrospun PVDF/MWCNT nanofibers with different MWCNT loadings and collection conditions Sample Code 2θ (°) Intensity (a.u.) 1-R-0% 20.49 632.8 2-R-0.05% 20.64 1848.2 3-R-0.2% 20.94 785.4 4-R-0.5% 20.84 1276.8 5-A-0% 20.69 1524.6 6-A-0.05% 20.54 2076.2 7-A-0.2% 20.59 1134.0 8-A-0.5% 20.79 1467.2 In contrast, samples containing 0.2%wt MWCNT exhibited reduced XRD peak intensity, suggesting suppression of effective β-phase formation. As discussed in the Introduction, this behavior can be attributed to increased solution viscosity and insufficient elongational force acting on the polymer jet, which limits chain alignment during electrospinning. A partial recovery of peak intensity was observed at 0.5%wt MWCNT, indicating that CNTs can still contribute to nucleation; however, the effect was less pronounced due to the onset of CNT agglomeration, in agreement with reports on CNT-filled PVDF systems [ 7 , 8 , 15 ]. This agglomeration behavior at higher loadings is a well-known challenge in nanotube composite processing [ 13 ]. The FT-IR spectra of samples are presented in Figs. 7 and 8 , respectively. The calculated β-phase fraction, summarized in Table 3 , showed good overall agreement with the XRD trends. Notably, the mechanically stretched sample containing 0.05%wt MWCNT exhibited the highest relative β-phase fraction (~ 78.5%), as estimated from FT-IR peak-area analysis. Minor inconsistencies between XRD peak intensity and FT-IR-derived β-phase percentages were observed for certain samples, particularly at higher CNT contents. These discrepancies were attributed to limitations in peak intensity analysis and experimental uncertainties in FT-IR measurements. To address this issue, the area under the FT-IR absorption curves was calculated for selected samples (Table 4 ), which confirmed that mechanically stretched samples consistently exhibited higher β-phase content than randomly collected ones. This result reinforces the conclusion that additional mechanical tension imposed by the rotating collector plays a decisive role in promoting β-phase formation, as previously reported in oriented electrospun PVDF systems [ 10 , 11 ] and supported by analyses of electrospinning-processing relationships [ 1 , 6 , 14 ]. Table 3 Relative β-phase fraction (F(β)) estimated from FT-IR peak-area analysis of the α-phase (763 cm⁻¹) and β-phase (840 cm⁻¹) absorption bands for electrospun PVDF/MWCNT nanofibers Sample Code F(β) (%) 1-R-0% 68 2-R-0.05% 71 3-R-0.2% 69 4-R-0.5% 74.54 5-A-0% 72 6-A-0.05% 78.5 7-A-0.2% 75 8-A-0.5% 72 Table 4 Integrated area of the β-phase FT-IR absorption band (~ 840 cm⁻¹) for selected PVDF/MWCNT samples, confirming enhanced β-phase content in mechanically stretched nanofibers Sample Code Peak Area (cm⁻¹) in 815–850 4-R-0.05% 416.06 7-A-0.2% 431.43 8-A-0.5% 473.47 Overall, the combined XRD and FT-IR analyses demonstrate that CNTs act as effective nucleating agents up to an optimal concentration of 0.05%wt, facilitating α-to-β phase transformation through electrostatic interactions between CF₂ dipoles of PVDF chains and the π-electron system of CNTs. Beyond this concentration, CNT agglomeration driven by van der Waals and π–π interactions reduces effective nucleation and limits further β-phase enhancement. These findings are in close agreement with the mechanisms proposed in the literature and provide a clear structure–processing–crystallinity relationship for electrospun PVDF/MWCNT nanofibrous composites. 4.4. Mechanical Properties of PVDF/MWCNT Nanofibrous Composites 4.4.1. Stress–Strain Behavior of PVDF/MWCNT Nanofibrous Mats The tensile stress–strain behavior of the electrospun PVDF/MWCNT nanofibrous composites was investigated to evaluate the intrinsic mechanical response of the materials under uniaxial loading. Representative stress–strain curves for selected samples are shown in Fig. 9 . For CNT-free samples, the randomly oriented PVDF nanofibers exhibited relatively low tensile strength and limited load-bearing capability, with a maximum stress of approximately 8 MPa. In contrast, the mechanically stretched PVDF nanofibers showed a substantially higher tensile strength (~ 16.7 MPa), indicating more efficient load transfer along the fiber axis. The incorporation of MWCNTs at low loading levels led to a pronounced enhancement in tensile strength. In particular, samples containing 0.05%wt MWCNT exhibited the highest stress values, reaching approximately 16.94 MPa for randomly collected fibers and 20.21 MPa for mechanically stretched fibers. This improvement can be attributed to the combined effects of CNT-induced reinforcement, improved interfacial interactions, and increased β-phase content, as discussed in Section 4.2 . The higher β-phase fraction, which is associated with increased chain rigidity and dipole alignment, contributes to the enhanced stiffness and strength of the nanofibrous mats. At higher CNT contents (0.2% and 0.5%wt), a gradual decrease in tensile strength was observed, particularly for randomly oriented samples. This reduction is attributed to CNT agglomeration and increased solution viscosity, which leads to defects in fiber structure and reduced effective stress transfer. However, these samples generally exhibited higher elongation at break, indicating increased flexibility and ductility under tensile loading. 4.4.2. Comparison Between Randomly Collected and Mechanically Stretched Nanofibers A direct comparison between randomly collected and mechanically stretched nanofibrous mats highlights the critical role of collector-induced orientation in determining mechanical performance. For all CNT contents, mechanically stretched nanofibers consistently exhibited higher tensile strength and improved mechanical stability compared to their randomly collected counterparts (Fig. 10 ). This behavior is attributed to the additional mechanical stretching imposed by the rotating collector during electrospinning, which promotes molecular chain orientation, reduces fiber waviness, and enhances stress transfer efficiency. The superiority of mechanically stretched fibers was most pronounced at the optimal CNT content of 0.05wt%, where the combined effects of stretch-induced orientation and CNT-induced nucleation resulted in the highest tensile strength and most uniform stress–strain response. These findings are consistent with previous studies reporting that oriented electrospun PVDF nanofibers exhibit enhanced mechanical robustness due to anisotropic reinforcement and improved molecular orientation—a direct outcome of mechanical stretching during collection [ 10 ], as demonstrated in high-performance devices [ 11 ] and functional fabrics [ 4 ]. This orientation maximizes the contribution of the high-modulus β-phase [ 3 ]. Even at higher CNT loadings, the mechanically stretched samples exhibited superior mechanical behavior compared to the randomly collected ones, underscoring the dominant influence of collector-induced mechanical stretching over compositional effects. 4.4.3. Implications of Mechanical Properties for Strain-Sensing Performance The observed mechanical behavior has direct implications for the strain-sensing performance of the PVDF/MWCNT nanofibrous composites. Higher tensile strength and mechanical stability enable the nanofibrous mats to withstand repeated deformation without structural failure, which is essential for reliable strain sensing. Moreover, the enhanced β-phase content and improved chain orientation in mechanically robust samples facilitate more efficient electromechanical coupling under applied strain. In particular, the mechanically stretched PVDF/MWCNT nanofibers containing 0.05%wt CNT exhibited an optimal balance between strength, flexibility, and crystalline structure. This combination allows effective stress transfer to piezoelectric domains while maintaining sufficient deformability to generate measurable electrical signals. Consequently, the mechanical reinforcement achieved through controlled CNT loading and collector-imposed mechanical stretching plays a crucial role in enhancing strain sensitivity, supporting the structure–property–performance relationship discussed in subsequent sections. 4.5. Piezoelectric Output and Strain Sensitivity 4.5.1. Dynamic Voltage Output and Sensitivity Analysis The piezoelectric output and strain-sensing performance of the electrospun PVDF/MWCNT nanofibrous composites were evaluated under controlled dynamic mechanical excitation. Figure 11 presents the time-dependent output voltage signals of samples with different CNT contents and collection conditions (random vs. mechanically stretched). All measurements were conducted under identical excitation conditions (applied force of 2.65 N and frequency of 5 Hz), enabling direct comparison. Pure PVDF nanofibers (sample 1-R-0%) generated a relatively low output voltage (~ 3.0 mV), reflecting limited piezoelectric activity due to the lower β-phase content discussed in Section 4.3 . A significant enhancement was observed upon MWCNT incorporation. The randomly collected sample containing 0.05wt% MWCNT (sample 2-R-0.05%) exhibited a maximum output voltage of approximately 3.93 mV, while the corresponding mechanically stretched sample (sample 6-A-0.05%) produced the highest output voltage of about 4.90 mV (Fig. 11 ). These results indicate that both CNT incorporation and mechanical stretching during collection contribute synergistically to improved piezoelectric performance. The strain sensitivity, defined as the ratio of output voltage to applied force (mV·N⁻¹), was calculated for all samples and is summarized in Table 5 . The highest sensitivity values were obtained for samples containing 0.05wt% MWCNT, reaching 1.48 mV·N⁻¹ for the randomly collected sample and 1.84 mV·N⁻¹ for the mechanically stretched sample. This trend mirrors the β-phase formation behavior identified in Section 4.3 , providing an initial indication that the piezoelectric output is strongly governed by crystalline structure. Table 5 Output voltage and strain sensitivity of electrospun PVDF/MWCNT nanofibrous sensors measured under a constant applied force of 2.65 N and excitation frequency of 5 Hz Sample Code Output Voltage (mV) Sensitivity (mV·N⁻¹) 1-R-0% 3.00 1.13 2-R-0.05% 3.93 1.48 3-R-0.2% 3.10 1.16 4-R-0.5% 3.45 1.30 5-A-0% 3.75 1.41 6-A-0.05% 4.90 1.84 7-A-0.2% 3.20 1.20 8-A-0.5% 3.60 1.35 At higher CNT contents (0.2 and 0.5wt%), a reduction in output voltage and sensitivity was observed for both randomly collected and mechanically stretched samples. Comparison between the two collection methods reveals that mechanically stretched samples consistently exhibit higher output voltage and sensitivity at identical CNT contents. The mechanically stretched PVDF/MWCNT nanofibers containing 0.05wt% CNT therefore demonstrate an optimal balance, yielding the highest absolute performance. 4.5.2. Structure–Property–Performance Relationship The experimental results demonstrate a clear and consistent relationship between processing parameters, material structure, and final piezoelectric performance. This relationship explains the optimal performance observed for the mechanically stretched 0.05wt% MWCNT sample (6-A-0.05%). Crystalline Structure as the Foundation As confirmed by XRD and FT-IR (Section 4.3 ), electrospinning promotes β-phase formation in PVDF, while low loadings of MWCNTs (≤ 0.05wt%) act as effective nucleating agents. The combination of mechanical stretching during collection and optimal CNT loading produced the highest β-phase fraction (~ 78.5%) and crystalline orientation. This enhanced polar phase content is the primary determinant of piezoelectric response, as the generated surface charge is directly proportional to the density of aligned dipoles within the material. Mechanical Robustness Enables Efficient Coupling Mechanical testing (Section 4.4 ) revealed a strong correlation between β-phase content and tensile performance. The mechanically stretched 0.05wt% CNT sample exhibited the highest tensile strength (~ 20.21 MPa), indicating efficient load transfer and structural integrity resulting from molecular orientation. This mechanical robustness is critical for a strain sensor; it allows the nanofibrous mat to withstand repeated deformation and ensures efficient transfer of applied stress to the piezoelectric crystalline domains, minimizing energy loss to viscoelastic dissipation. The Dual Role of CNTs and the Percolation Limit Carbon nanotubes play a dual role. At the optimal concentration (0.05wt%), they act as nucleating agents for the β-phase [ 6 , 8 ] and form localized conductive pathways that facilitate charge collection without reaching full electrical percolation [ 13 ]. The electrical conductivity of this optimal sample (~ 10⁻⁷ S·m⁻¹) falls within a range that enhances signal output without short-circuiting the piezoelectric potential [ 8 , 13 ]. At higher CNT contents (≥ 0.2wt%), agglomeration (as seen in SEM analysis, Section 4.2 ) disrupts this synergy. Agglomerates act as defects that hinder stress transfer, reduce effective nucleation sites, and can create charge leakage pathways, leading to increased dielectric losses and diminished piezoelectric voltage output despite higher bulk conductivity [ 7 , 8 , 13 ]. The Critical Role of Mechanical Stretching The superior performance of mechanically stretched fibers, even at identical CNT loadings, is attributed to the collector-imposed tensile force. This stretching refines fiber morphology (Section 4.2 ), enhances molecular chain and dipole alignment along the fiber axis [ 10 , 11 ], and improves the mechanical properties necessary for durable sensing (Section 4.4 ). This alignment maximizes the projection of the applied stress onto the polar axis of the β-phase crystals, leading to more efficient electromechanical conversion. In summary, the peak strain sensitivity of the stretched PVDF/MWCNT (0.05wt%) nanofibers is not the result of a single factor, but the synergistic outcome of a processing-structure-property triad: mechanical stretching induces optimal morphology and β-phase orientation, which is further nucleated and stabilized by well-dispersed CNTs. This structure simultaneously provides the high piezoelectric activity, mechanical durability, and balanced electrical conductivity required for a high-performance, flexible strain sensor. 5. Strain-Sensing Mechanism The strain-sensing behaviour of the electrospun PVDF/MWCNT nanofibrous composites arises from the combined effects of intrinsic piezoelectricity and CNT-assisted electromechanical charge transport. Under applied mechanical deformation, the oriented β-phase dipoles in PVDF generate polarization charges proportional to the applied strain, in accordance with linear piezoelectric theory. This mechanism dominates at low mechanical stresses, where the electrical output scales linearly with deformation, as observed in the voltage–time responses (Fig. 11 ) and sensitivity values (Table 5 ). Carbon nanotubes play a dual role in this sensing mechanism. First, CNTs act as nucleating agents during electrospinning, promoting α-to-β phase transformation and increasing dipole density within the nanofibers [ 6 , 8 ]. Second, at optimized concentrations (0.05%wt), CNTs facilitate effective charge distribution and collection by forming localized conductive pathways without reaching full electrical percolation [ 13 ]. This enhances signal stability and amplifies the measurable voltage output without short-circuiting the piezoelectric response, consistent with mechanisms proposed in previous PVDF/CNT studies [ 8 ]. Mechanical stretching during collection further amplifies the strain-sensing response by improving stress transfer efficiency and promoting molecular orientation, where dipole orientation is maximized [ 10 ]. Mechanically stretched nanofibers, therefore, exhibit higher and more stable output signals than randomly collected mats at identical CNT contents, as demonstrated by the superior performance of sample 6-A-0.05% compared to sample 2-R-0.05%. This enhanced response is consistent with earlier reports on oriented electrospun PVDF nanofibers for sensing applications [ 11 ], a principle leveraged in modern high-performance piezoelectric fabrics and composite fibers [ 4 , 7 ]. At higher CNT loadings (> 0.05%wt), CNT agglomeration and increased dielectric losses reduce effective polarization and disrupt uniform stress transfer, leading to diminished piezoelectric output despite higher conductivity. This behaviour highlights the importance of operating below the percolation threshold to preserve the dominance of the piezoelectric mechanism over purely resistive effects. The sensing response is dominated by the piezoelectric effect, as measurements were performed under dynamic loading without DC bias. In summary, the strain-sensing mechanism in PVDF/MWCNT nanofibrous composites is governed by a synergistic interaction between electrospinning-induced β-phase polarization, CNT-assisted charge transport, and mechanical stretching-induced orientation. Optimizing these parameters enables high sensitivity, mechanical durability, and signal stability, making the developed nanofibrous composites promising candidates for flexible and wearable strain-sensing applications. Conclusion In this study, PVDF/MWCNT nanofibrous composites were successfully fabricated via electrospinning to systematically investigate the synergistic effects of in-process mechanical stretching and CNT incorporation on piezoelectric strain sensitivity. The key findings are summarized as follows: Through comprehensive structural analysis (XRD, FT-IR), we established that electrospinning inherently promotes the electroactive β-phase in PVDF. The addition of low-loading MWCNTs (0.05wt%) further enhanced this transformation via nucleation, while the mechanical stretching imposed by a rotating collector (500 rpm) significantly improved molecular and dipole alignment. This combined effect yielded the highest relative β-phase fraction (~ 78.5%) and crystalline orientation. The optimized crystalline structure directly translated to superior mechanical and electromechanical properties. The mechanically stretched composite with 0.05wt% CNT exhibited the highest tensile strength (~ 20.21 MPa) and, under dynamic loading, generated a peak output voltage of ~ 4.9 mV with a strain sensitivity of 1.84 mV·N⁻¹. This performance represents a clear processing–structure–property relationship: mechanical stretching refines morphology and orientation, while optimally dispersed CNTs nucleate the β-phase and facilitate charge collection without reaching electrical percolation. The results identify the optimal fabrication parameters as an 18wt% PVDF concentration, 0.05wt% MWCNT loading, and collection under moderate mechanical stretching (500 rpm). This approach provides a scalable and effective route to engineer flexible piezoelectric nanofibers. The resulting composites, which balance high sensitivity, durability, and flexibility, demonstrate strong potential for application in next-generation wearable electronics, structural health monitoring systems, and advanced human–machine interfaces. Declarations Data Availability : The data used to support the findings of this study are included within the article. Clinical trial number: Not applicable. Conflict of interest : The authors declare no conflict of interest. Funding: There was no funding for this work. Author Contribution : Atiyeh Amirhosseini: Methodology, Investigation, Writing – original draft. Mahdi Nouri : Conceptualization, Supervision. Mostafa Jamshidi Avanaki : Supervision, Conceptualization, Methodology, Investigation, review & editing–original draft. All authors discussed the results and commented on the manuscript. References Sharma S, Mishra SS, Kumar R, Yadav RM (2022) Recent progress on polyvinylidene difluoride-based nanocomposites: applications in energy harvesting and sensing. New J Chem 46:18613-18646. https://doi.org/10.1039/D2NJ00002D Zhang H, Ji X, Wang Z, Tang S, Wang Z, Zhu W (2026) Advances in intelligent polyvinylidene fluoride-based piezoelectric composites for self-powered wearable electronics. Small 22:e09387. https://doi.org/10.1002/smll.202509387 Ruan L, Yao X, Chang Y, Zhou L, Qin G, Zhang X (2018) Properties and applications of the β phase poly(vinylidene fluoride). Polymers 10:228. https://doi.org/10.3390/polym10030228 Zhu J, Zhang X, Yang G, Su F, Ali S, Dai K, Liu C (2025) Nanofibrous PVDF-based smart flexible fabrics with high piezoelectric properties for human motion monitoring. ACS Appl Polym Mater 7:5501-5509. https://doi.org/10.1021/acsapm.5c00267 Zhou S, Zhao Z, Wang Z, Yang L (2026) Hybrid piezo-triboelectric porous PVDF/CNT/PDMS pressure sensor enabling surface-defect and texture recognition. Int J Mod Phys B 40:2650033. https://doi.org/10.1142/S0217979226500335 He Z, Rault F, Lewandowski M, Mohsenzadeh E, Salaün F (2021) Electrospun PVDF nanofibers for piezoelectric applications: A review of the influence of electrospinning parameters on the β phase and crystallinity enhancement. Polymers 13:174. https://doi.org/10.3390/polym13020174 Liu ZH, Pan CT, Lin LW, Lai HW (2013) Piezoelectric properties of PVDF/MWCNT nanofiber using near-field electrospinning. Sens Actuators A Phys 193:13-24. https://doi.org/10.1016/j.sna.2013.01.007 Utchimahali Muthu Raja P, Shenthilkumar RR, Kausalya Sasikumar G (2025) Structural optimization and piezoelectric performance of PVDF/MWCNT nanocomposites for wearable sensor applications. Microchem J 219:115841. https://doi.org/10.1016/j.microc.2025.115841 Bai Y, Liu Y, Lv H, Shi H, Zhou W, Liu Y, Yu D-G (2022) Processes of electrospun polyvinylidene fluoride-based nanofibers, their piezoelectric properties, and several fantastic applications. Polymers 14:4311. https://doi.org/10.3390/polym14204311 Yuan H, Zhou Q, Zhang Y (2025) Improving fibre alignment during electrospinning. In: Afshari M (ed) Electrospun nanofibers, 2nd edn. Elsevier, Amsterdam, pp 91-113. https://doi.org/10.1016/C2022-0-03204-9 Persano L, Dagdeviren C, Su Y, Zhang Y, Girardo S, Pisignano D, Huang Y, Rogers JA (2013) High performance piezoelectric devices based on aligned arrays of nanofibers of poly(vinylidenefluoride-co-trifluoroethylene). Nat Commun 4:1633. https://doi.org/10.1038/ncomms2639 Panditkar SS, Gurnule WB, Waghe PU, Gurnule PW, Kumar P (2026) The art and science of electrospinning: a detailed review of process and potential applications. Polym Bull 83:53. https://doi.org/10.1007/s00289-025-06071-0 Huang YY, Terentjev EM (2012) Dispersion of carbon nanotubes: mixing, sonication, stabilization, and composite properties. Polymers 4:275-295. https://doi.org/10.3390/polym4010275 Kalimuldina G, Turdakyn N, Abay I, Medeubayev A, Nurpeissova A, Adair D, Bakenov Z (2020) A review of piezoelectric PVDF film by electrospinning and its applications. Sensors 20:5214. https://doi.org/10.3390/s20185214 Yu H, Huang T, Lu M, Mao M, Zhang Q, Wang H (2013) Enhanced power output of an electrospun PVDF/MWCNTs-based nanogenerator by tuning its conductivity. Nanotechnology 24:405401. https://doi.org/10.1088/0957-4484/24/40/405401 Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 03 Mar, 2026 Reviewers invited by journal 03 Mar, 2026 Editor invited by journal 27 Feb, 2026 Editor assigned by journal 23 Feb, 2026 First submitted to journal 20 Feb, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8916823","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":599876368,"identity":"cdb4a0e7-0601-476d-8849-02cbf2c76175","order_by":0,"name":"Atiyeh Amirhosseini","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Atiyeh","middleName":"","lastName":"Amirhosseini","suffix":""},{"id":599876369,"identity":"b8804d7f-7949-43ad-a877-41d3e69508ad","order_by":1,"name":"Mahdi Nouri","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Mahdi","middleName":"","lastName":"Nouri","suffix":""},{"id":599876370,"identity":"ee764ecc-6815-4755-ba2a-21f159d8ebd2","order_by":2,"name":"Mostafa Jamshidi Avanaki","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+0lEQVRIiWNgGAWjYHCCBCA+wMNwmPkAA4OBBVTQgCgtbECGgQRRWkDgAEgXSJkEIZUMDLoNDA8/3fhzR4bvOM/n1zwFEvLmDMwPPzAU3MOpxewAQ7J0btszHsnDvNuseQwkDHc2sBlLMBgU49OSIJ3bcJjHAKjFGKiFccMBBjOgXxLw2vI75w9IC88zkBb7DQfYvxHSkiadwwbWwvwYqCVxwwEeArYcZkizzm07DPQLmxnjHAOJ5A2HeYolEvBpOd6TfBvoMHu+84cff3jzx8Z2w/H2jR8+/MGthYGZBy7JBokUZgZI9OIG7Afguj/gVTgKRsEoGAUjFgAAXfxRoPBycMcAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0003-3829-5257","institution":"University of Guilan","correspondingAuthor":true,"prefix":"","firstName":"Mostafa","middleName":"Jamshidi","lastName":"Avanaki","suffix":""}],"badges":[],"createdAt":"2026-02-19 11:06:00","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8916823/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8916823/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":104402960,"identity":"3010a570-dbbc-4200-9e3a-6f57749635c5","added_by":"auto","created_at":"2026-03-11 12:17:00","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":59661,"visible":true,"origin":"","legend":"\u003cp\u003ePiezoelectric testing setup: (a) Schematic of the loading configuration; (b) Photograph of the pressure loading device\u003c/p\u003e","description":"","filename":"image1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8916823/v1/6e3d780c2f0b751ccd7c36cb.jpeg"},{"id":104101378,"identity":"97666efd-da74-43b3-a9f1-12b38de889d6","added_by":"auto","created_at":"2026-03-06 19:47:34","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":255874,"visible":true,"origin":"","legend":"\u003cp\u003eScanning electron microscopy (SEM) images of electrospun PVDF nanofibers at different polymer concentrations: (a) 12wt%, (b) 15wt%, and (c) 18wt%\u003c/p\u003e","description":"","filename":"image2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8916823/v1/23a4a269428b2e6ac27c2e1b.jpeg"},{"id":104101382,"identity":"57fe1926-77e7-4492-9f53-f2a0410891e1","added_by":"auto","created_at":"2026-03-06 19:47:34","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":289320,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images and corresponding fiber diameter distribution histograms of electrospun PVDF/MWCNT nanofibers (18wt% PVDF, randomly collected) with different MWCNT contents: (a) 0wt%, (b) 0.05wt%, (c) 0.2wt%, and (d) 0.5wt%\u003c/p\u003e","description":"","filename":"image3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8916823/v1/3dddf65eca5f3817a74f8397.jpeg"},{"id":104402812,"identity":"b1ae0392-8a9c-4419-9794-1bfcdca17c0e","added_by":"auto","created_at":"2026-03-11 12:16:32","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":281093,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images and corresponding fiber diameter distribution histograms of electrospun PVDF/MWCNT nanofibers (18wt% PVDF,\u003cstrong\u003e mechanically stretched)\u003c/strong\u003e with different MWCNT contents: (a) 0wt%, (b) 0.05wt%, (c) 0.2wt%, and (d) 0.5wt%\u003c/p\u003e","description":"","filename":"image4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8916823/v1/777341dac7b05d1901951be4.jpeg"},{"id":104402913,"identity":"0d2190e3-baf2-4a7a-a636-062b1707f906","added_by":"auto","created_at":"2026-03-11 12:16:53","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":98540,"visible":true,"origin":"","legend":"\u003cp\u003eX‑ray diffraction (XRD) patterns of PVDF/MWCNT nanofibrous composites with different MWCNT loadings and collection conditions: randomly collected (R) and mechanically stretched (A)\u003c/p\u003e","description":"","filename":"image5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8916823/v1/ae4fea031874a9ebd1327c1e.jpeg"},{"id":104403029,"identity":"81a765ba-e890-4e52-b3e4-7f46fc98139d","added_by":"auto","created_at":"2026-03-11 12:17:14","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":154279,"visible":true,"origin":"","legend":"\u003cp\u003eIntensity of the β‑phase diffraction peak (2θ ≈ 20–21°) for electrospun PVDF/MWCNT nanofibers, comparing \u003cstrong\u003erandomly collected (R)\u003c/strong\u003e and \u003cstrong\u003emechanically stretched (A)\u003c/strong\u003e samples across different MWCNT loadings (0–0.5wt%)\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-8916823/v1/51fb8de1b3c709ce6d4fe0bb.png"},{"id":104101386,"identity":"b7755d85-179d-4750-8b59-034e9fbbf44d","added_by":"auto","created_at":"2026-03-06 19:47:34","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":130300,"visible":true,"origin":"","legend":"\u003cp\u003eFT‑IR spectra of randomly collected PVDF/MWCNT nanofibers (samples 1‑4) showing the characteristic absorption bands of the α‑phase (~763 cm⁻¹) and β‑phase (~840 cm⁻¹) at increasing MWCNT loadings (0, 0.05, 0.2, 0.5wt%)\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-8916823/v1/55adff4b37fe0f57d92c2abf.png"},{"id":104101385,"identity":"85f53980-7646-4c92-a214-a1f77b3090c8","added_by":"auto","created_at":"2026-03-06 19:47:34","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":148056,"visible":true,"origin":"","legend":"\u003cp\u003eFT‑IR spectra of \u003cstrong\u003emechanically stretched\u003c/strong\u003e PVDF/MWCNT nanofibers (samples 5‑8) showing the characteristic absorption bands of the α‑phase (~763 cm⁻¹) and β‑phase (~840 cm⁻¹) at increasing MWCNT loadings (0, 0.05, 0.2, 0.5wt%)\u003c/p\u003e","description":"","filename":"image8.png","url":"https://assets-eu.researchsquare.com/files/rs-8916823/v1/e0bec0f410a18ab43da9a6a9.png"},{"id":104403206,"identity":"63a179bc-78cb-4980-9e73-9e7b516b1fd1","added_by":"auto","created_at":"2026-03-11 12:17:44","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":249952,"visible":true,"origin":"","legend":"\u003cp\u003eRepresentative stress–strain curves of electrospun PVDF/MWCNT nanofibers comparing\u003cstrong\u003e randomly collected (dashed lines) \u003c/strong\u003eand \u003cstrong\u003emechanically stretched (solid lines)\u003c/strong\u003e samples at different MWCNT loadings: (a) 0wt%, (b) 0.05wt%, (c) 0.2wt%, and (d) 0.5wt%\u003c/p\u003e","description":"","filename":"image9.png","url":"https://assets-eu.researchsquare.com/files/rs-8916823/v1/648c6b93c4e22461aa0565e6.png"},{"id":104101387,"identity":"adf8bcd7-7da3-4793-b2b7-6707470f792f","added_by":"auto","created_at":"2026-03-06 19:47:34","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":91235,"visible":true,"origin":"","legend":"\u003cp\u003eStress–strain curves comparing all \u003cstrong\u003erandomly collected\u003c/strong\u003e (samples 1‑4) and \u003cstrong\u003emechanically stretched\u003c/strong\u003e (samples 5‑8) PVDF/MWCNT nanofibers, showing the effect of MWCNT loading (0–0.5wt%) and collection method on tensile behavior\u003c/p\u003e","description":"","filename":"image10.png","url":"https://assets-eu.researchsquare.com/files/rs-8916823/v1/fe3da347f5c93e569511b671.png"},{"id":104101383,"identity":"0be3c8b9-9000-4ac9-b372-e4a90d193426","added_by":"auto","created_at":"2026-03-06 19:47:34","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":279031,"visible":true,"origin":"","legend":"\u003cp\u003eDynamic output voltage signals of PVDF/MWCNT composite nanofibers under cyclic loading (2.65 N, 5 Hz), comparing \u003cstrong\u003erandomly collected\u003c/strong\u003e and \u003cstrong\u003emechanically stretched\u003c/strong\u003e samples at MWCNT loadings of 0, 0.05, 0.2, and 0.5wt%\u003c/p\u003e","description":"","filename":"image11.png","url":"https://assets-eu.researchsquare.com/files/rs-8916823/v1/c22277e5326329ec2991820d.png"},{"id":104408506,"identity":"7c78481f-330f-4596-a1f0-7cc83c1d71a2","added_by":"auto","created_at":"2026-03-11 12:42:45","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3386394,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8916823/v1/ad9d4b2b-86cc-4e47-a9c6-bc91171bb2a3.pdf"}],"financialInterests":"","formattedTitle":"Enhanced Piezoelectric Strain Sensitivity in Electrospun PVDF/MWCNT Nanofibers via Moderate Mechanical Stretching and β-Phase Orientation","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe rapid expansion of flexible electronics, wearable technologies, and intelligent structural health monitoring systems has stimulated extensive research into polymer-based piezoelectric materials capable of converting mechanical stimuli into electrical signals [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Among these materials, polyvinylidene fluoride (PVDF) has emerged as one of the most promising piezoelectric polymers owing to its low density, mechanical flexibility, chemical resistance, and excellent electromechanical coupling [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. These attributes make PVDF particularly attractive for pressure sensors, self-powered devices, and smart textile applications [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePVDF is a semi-crystalline polymer that can crystallize into several polymorphic phases, including α, β, γ, δ, and ε [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Among them, the β phase exhibits the highest polarity due to its all-trans molecular conformation and is therefore primarily responsible for the piezoelectric, ferroelectric, and pyroelectric properties of PVDF [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Recent studies on composite systems have further confirmed that the β-phase fraction directly governs the piezoelectric coefficient and strain sensitivity of PVDF-based sensors [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Consequently, the sensitivity and efficiency of PVDF-based sensors are strongly dependent on the β-phase fraction, making its enhancement a central objective in the design of high-performance piezoelectric materials [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eElectrospinning has proven to be an effective and scalable technique for inducing and aligning the β-phase in PVDF nanofibers without the need for post-poling treatments [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. The strong electric field, combined with elongational forces acting on the polymer jet, promotes molecular chain and dipole orientation along the fiber axis, leading to self-polarized nanofibrous structures [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. This inherent control over morphology also yields fibers with high surface area, porosity, and breathability\u0026mdash;attributes that are critical for integration into wearable and flexible sensing systems [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn addition to processing conditions, the mechanical stretching and orientation of nanofibers during collection plays a crucial role in determining the crystalline structure and piezoelectric response of electrospun PVDF [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The use of rotating collectors during electrospinning introduces controlled mechanical stretching, resulting in improved molecular orientation, reduced fiber diameter, and increased β-phase content compared to randomly collected fibers [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Several studies have demonstrated that this induced orientation through mechanical stretching significantly enhances both mechanical strength and piezoelectric sensitivity [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], although it is noted that excessively high rotation speeds may cause fiber breakage and structural defects [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe incorporation of carbon nanotubes (CNTs) into PVDF matrices provides another effective strategy for enhancing electromechanical performance. CNTs can act as nucleating agents that promote α-to-β phase transformation through strong interfacial interactions with PVDF chains [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], while simultaneously improving mechanical reinforcement and electrical conductivity when dispersed below the electrical percolation threshold [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Recent investigations have shown that optimized CNT loading in electrospun PVDF fibers enables enhanced strain sensitivity, stability under cyclic loading, and multifunctional sensing capabilities, including pressure, motion, and respiration detection [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDespite significant progress in electrospun PVDF-based piezoelectric materials [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], a systematic understanding of the combined effects of electrospinning-induced jet stretching, collector-imposed mechanical stretching, and carbon nanotube (CNT) loading on β-phase formation and strain-sensing performance remains incomplete. In particular, the interdependent roles of CNT-induced nucleation and electrospinning-induced chain orientation in governing the electromechanical response of PVDF nanofibers have not been fully clarified. The objective of this study is to elucidate the synergistic roles of electrospinning-induced mechanical stretching and molecular orientation and MWCNT incorporation in governing the morphology, crystalline phase evolution, mechanical properties, and strain-sensing performance of PVDF nanofibrous composites. By systematically varying CNT content (0\u0026ndash;0.5wt%) and collector-induced mechanical stretching, this work clarifies the interplay between CNT-induced β-phase nucleation, stretching-induced molecular orientation, mechanical reinforcement, and their combined effect on piezoelectric strain sensitivity.\u003c/p\u003e \u003cp\u003eThrough comprehensive structural, mechanical, and piezoelectric characterization, the study seeks to identify optimal material compositions and processing parameters that maximize strain sensitivity while preserving mechanical flexibility and stability. This approach is designed to advance the development of efficient and scalable PVDF-based piezoelectric strain sensors.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Materials\u003c/h2\u003e \u003cp\u003ePolyvinylidene fluoride (PVDF) powder (Kynar 761, Mw\u0026thinsp;\u0026asymp;\u0026thinsp;520,000g\u0026middot;mol⁻\u0026sup1;), a semi-crystalline polymer with a melting temperature of 165\u0026ndash;172\u0026deg;C, was used as the matrix material. Multi-walled carbon nanotubes (MWCNTs) with a purity above 98%, an outer diameter of 10\u0026ndash;20nm, an average length of ~\u0026thinsp;30\u0026micro;m, a specific surface area of 150 m\u0026sup2;\u0026middot;g⁻\u0026sup1;, ~\u0026thinsp;2% surface \u0026ndash;COOH functionalization, and less than 1.5%wt ash content were employed as conductive fillers and nucleating agents. N, N-dimethyl formamide (DMF) and acetone (both from Merck, Germany) were used as solvents. Solution preparation involved precise weighing using analytical balances, magnetic stirring, and ultrasonic dispersion.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Preparation of PVDF/MWCNT Electrospinning Solutions\u003c/h2\u003e \u003cp\u003eTo achieve uniform dispersion of carbon nanotubes and minimize agglomeration, the electrospinning solutions were prepared using a two-step mixing strategy, as recommended in previous studies on CNT composite processing [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] and applied in PVDF/MWCNT systems [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. First, a neat PVDF solution was prepared by dissolving PVDF powder in a mixed solvent system consisting of acetone and DMF at a volume ratio of 4:6. The solution was placed on a hot plate equipped with a magnetic stirrer and heated to 50\u0026deg;C for 5minutes then at room temperature for 1h to obtain a homogeneous polymer solution.\u003c/p\u003e \u003cp\u003eFor the preparation of CNT-containing solutions, predetermined amounts of MWCNTs corresponding to weight fractions of 0.05, 0.2, and 0.5%wt relative to PVDF were accurately weighed and dispersed in acetone/DMF solvent mixture (4:6 v/v). MWCNT loading is reported as %wt relative to PVDF mass (MWCNT/PVDF \u0026times; 100). To achieve homogeneous dispersion, the solution was placed in an ultrasonic bath for 40 minutes at 50\u0026deg;C. Subsequently, the CNT dispersion and PVDF solution were combined and magnetically stirred for 35min at room temperature to obtain stable and uniform PVDF/MWCNT electrospinning solutions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Electrospinning Process and Nanofiber Fabrication\u003c/h2\u003e \u003cp\u003eElectrospinning was carried out using a syringe-based electrospinning system equipped with a high-voltage power supply and a rotating collector. The prepared solutions were loaded into a syringe fitted with a metallic needle and delivered at a constant flow rate of 1mL\u0026middot;h⁻\u0026sup1;. Electrospinning was performed with a needle-to-collector distance of 18cm. A voltage of 18\u0026ndash;19kV was applied between the needle (positive electrode) and the collector (negative electrode), and electrospinning was performed for 4h under controlled environmental conditions (T: 25\u0026ndash;26\u0026deg;C; RH: 60\u0026ndash;65% for all samples). Partially aligned/oriented nanofibers were collected using a rotating drum collector operating at 500rpm to impart controlled mechanical stretching, while random mats were obtained by operating the same collector at a minimal speed, consistent with established techniques for inducing fiber orientation. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The rotation of the collector at 500rpm was employed to impart controlled mechanical stretching to the polymer jet. This induced partial fiber alignment and promoted molecular chain orientation during solidification, while avoiding the excessive speeds that can lead to fiber breakage. This approach allows investigation of the effects of in-process tensile forces on fiber properties. For preliminary observation of fiber morphology, electrospinning was performed onto glass slides for 15min, and the samples were examined using an optical microscope.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Characterization Techniques","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Morphological Analysis, Structural and Phase Characterization\u003c/h2\u003e \u003cp\u003eSurface morphology and diameter of the nanofibers prepared by electrospinning were evaluated using scanning electron microscopy (SEM). The dispersion and average diameter of the nanofibers were measured using ImageJ software. Then, statistical calculations and relevant graphs were made using Origin Project software. XRD test was used to measure the formation of β phase, and FT-IR spectroscopy was used to calculate and examine the amount of formation of the polar β phase.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Phase Identification and β-Phase Quantification by FT-IR\u003c/h2\u003e \u003cp\u003eThe crystalline phases of PVDF in the prepared nanofibrous composites were analyzed using Fourier-transform infrared (FT-IR) spectroscopy, which is a widely used technique for distinguishing the electroactive β-phase from the non-polar α-phase of PVDF based on characteristic vibrational absorption bands. The electroactive β-phase was identified using the characteristic absorption band located at approximately 840cm⁻\u0026sup1;, which is attributed to CF₂ stretching vibrations associated with the all-trans (TTTT) molecular conformation of PVDF. The α-phase contribution was identified using the absorption band at approximately 763cm⁻\u0026sup1;, corresponding to CF₂ bending and skeletal vibrations of the trans\u0026ndash;gauche\u0026ndash;trans\u0026ndash;gauche\u0026prime; (TGTG\u0026prime;) conformation [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. This established spectroscopic method has been widely used for phase quantification in PVDF and its nanocomposites [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. These peaks were selected because they are well separated, minimally affected by peak overlap, and are commonly used in the literature for semi-quantitative phase analysis of PVDF. All FT-IR spectra were baseline-corrected in the range of 700\u0026ndash;900cm⁻\u0026sup1; prior to analysis. The areas under the absorption peaks at ~\u0026thinsp;763cm⁻\u0026sup1; and ~\u0026thinsp;840cm⁻\u0026sup1; were calculated by numerical integration using identical integration limits for all samples. Peak area analysis was used instead of peak height measurement to reduce the influence of noise, peak broadening, and minor spectral shifts caused by CNT incorporation or processing variations. The relative β-phase fraction (F\u003csub\u003eβ\u003c/sub\u003e) was estimated using the following relationship [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]:\u003c/p\u003e \u003cp\u003eF\u003csub\u003eβ\u003c/sub\u003e = A\u003csub\u003eβ\u003c/sub\u003e / (K\u003csub\u003eβ\u003c/sub\u003e/K\u003csub\u003eα\u003c/sub\u003e * A\u003csub\u003eα\u003c/sub\u003e + A\u003csub\u003eβ\u003c/sub\u003e) (1)\u003c/p\u003e \u003cp\u003ewhere A\u003csub\u003eα\u003c/sub\u003e and A\u003csub\u003eβ\u003c/sub\u003e are the integrated absorbances of the α-phase (763cm⁻\u0026sup1;) and β-phase (840cm⁻\u0026sup1;) bands, respectively, and K\u003csub\u003eα\u003c/sub\u003e (6.1 \u0026times; 10⁴ cm\u0026sup2; mol⁻\u0026sup1;) and K\u003csub\u003eβ\u003c/sub\u003e (7.7 \u0026times; 10⁴ cm\u0026sup2; mol⁻\u0026sup1;) are the absorption coefficients at the respective wavenumbers.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Mechanical Characterization of composite nanofibers\u003c/h2\u003e \u003cp\u003eTo perform tensile strength testing, samples were stretched between two jaws using an Instron machine, with a stretching speed of 5mm/min and a working distance of 20mm between the two jaws. To place the nanofibers between the two jaws of the machine, paper frames of 40*40 mm\u003csup\u003e2\u003c/sup\u003e were prepared, and 30*5 mm\u003csup\u003e2\u003c/sup\u003e samples were mounted and secured over a square cut in the middle of the frame using a thin layer of adhesive. The raw force\u0026ndash;elongation data from the Instron universal testing machines were processed to calculate the corresponding engineering stress and strain. These values were used to determine the tensile strength and to generate the stress\u0026ndash;strain curves.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.4. Piezoelectric and Strain-Sensing Measurements\u003c/h2\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e3.4.1. Experimental Setup for Dynamic Piezoelectric Testing\u003c/h2\u003e \u003cp\u003eA custom-built cyclic compression apparatus was used to apply controlled dynamic force and simultaneously measure the piezoelectric voltage output (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The system consists of a DC motor coupled to an eccentric cam. The rotation of the cam converts the motor's rotary motion into a sinusoidal vertical displacement, which is transmitted through a rigid plunger to apply compressive force to the sample. The electrospun nanofibrous mat (1 \u0026times; 1 cm\u0026sup2;) was sandwiched between two aluminum foil electrodes (0.01 mm thickness) and placed on a flat, rigid base. A calibrated piezoelectric load cell was positioned between the base and the lower electrode to measure the applied force in real time. The DC motor's speed was regulated to achieve a consistent loading frequency of 5 Hz. The eccentricity of the cam was adjusted to produce a peak compressive force of 2.65 N\u0026mdash;a magnitude chosen to represent moderate, application-relevant stress while ensuring a clear signal output. This target force was verified in real-time by the load cell, ensuring consistent stimulation across all samples. The open-circuit voltage generated by the sample was acquired using a high-impedance digital oscilloscope (GDS-1102, GW-Instek). The voltage signal from the sample and the force signal from the load cell were recorded synchronously, enabling direct correlation between mechanical input and electrical output.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e3.4.2. Data Analysis and Sensitivity Evaluation\u003c/h2\u003e \u003cp\u003eThe voltage\u0026ndash;time and force\u0026ndash;time signals were recorded synchronously by the oscilloscope. For each sample, testing was repeated for at least three loading cycles under stable conditions (n\u0026thinsp;\u0026ge;\u0026thinsp;3). The peak output voltage (V\u003csub\u003eout​\u003c/sub\u003e) was extracted as the absolute maximum of the steady-state voltage signal at the driving frequency (5 Hz). The peak force (F), corresponding to the timing of V\u003csub\u003eout​\u003c/sub\u003e, was recorded simultaneously from the load cell. The piezoelectric strain sensitivity (\u003cem\u003eS\u003c/em\u003e) was calculated as S=V\u003csub\u003eout​\u003c/sub\u003e/F. Mean values and standard deviations of V\u003csub\u003eout​\u003c/sub\u003e and \u003cem\u003eS\u003c/em\u003e were derived from the repeated measurements for each sample.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"4. Results and Discussion","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e4.1. Optimization of PVDF Concentration\u003c/h2\u003e \u003cp\u003eNanofibrous samples prepared from different PVDF/MWCNT compositions were labelled according to their formulation and processing conditions. Solutions with concentrations of 12%, 15%, 18% and 20% by weight of PVDF with the same process settings were selected for electrospinning with random orientation. In the solution containing 20% by weight of PVDF, the high concentration increased the viscosity and gelation of the solution, its coagulation at the needle tip, lack of movement towards the collector, and consequently disrupted the electrospinning process, and no nanofibers were formed. In Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, SEM images of the concentrations of 12%, 15% and 18% by weight are given. Electrospinning of the 12% by weight solution was accompanied by high spattering during the electrospinning process and, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, bead formation was observed in some samples. By examining the SEM images and calculating the average diameter of the nanofibers of each group, the average diameters were 406.53, 538.20, and 870.76 nm for the 12%, 15% and 18%wt samples, respectively. According to the previous studies, among the 15% and 18%wt concentrations that consisted of more uniform fibers and very little beads, the higher concentration (18%wt) was selected as the selected concentration to achieve nanofibers with a more uniform morphology and structure, for the preparation of all subsequent samples.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e4.2. Effect of Electrospinning and CNT Content on Nanofiber Morphology\u003c/h2\u003e \u003cp\u003eThe effect of carbon nanotube (CNT) loading and collector type on the morphology and diameter distribution of electrospun PVDF/MWCNT nanofibers was systematically investigated using SEM analysis. Representative SEM images and corresponding diameter frequency distributions for randomly collected nanofibers are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, while Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e present the results for nanofibers subjected to mechanical stretching using a rotating drum collector.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEffect of MWCNT loading and collection condition on the average diameter of electrospun PVDF/MWCNT nanofibers\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample Code\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCollector Speed (rpm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePVDF\u003c/p\u003e \u003cp\u003e(%wt)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMWCNT (%wt)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMean Diameter (nm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eStd. Deviation (nm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eDiameter Range (nm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT1-R-0%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e406.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e133.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e250\u0026ndash;350\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT2-R-0%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e538.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e178.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e450\u0026ndash;550\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1-R- 0%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e870.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e165.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e700\u0026ndash;900\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2-R-0.05%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1087.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e222.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1000\u0026ndash;1400\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3-R-0.2%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1219.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e245.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1000\u0026ndash;1400\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4-R-0.5%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e973.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e245.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e800\u0026ndash;1100\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5-A-0%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e503.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e152.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e350\u0026ndash;600\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6-A-0.05%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e397.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e96.81\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e300\u0026ndash;600\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7-A-0.2%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e607.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e161.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e400\u0026ndash;650\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8-A-0.5%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e487.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e123.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e400\u0026ndash;600\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFor pure PVDF nanofibers prepared with a random collector (sample 1-R-0%), the fibers exhibited a broad diameter distribution ranging from approximately 344 to 1304 nm, with an average diameter of 876.8\u0026thinsp;\u0026plusmn;\u0026thinsp;165.5 nm and the highest frequency in the range of 700\u0026ndash;1100 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). Upon incorporation of 0.05%wt MWCNT (sample 2-R-0.05%), denser fibrous regions were observed (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb), indicating improved spinnability; however, the average diameter increased to 1087.3\u0026thinsp;\u0026plusmn;\u0026thinsp;222.6 nm. This increase is attributed to the rise in solution viscosity caused by CNT addition [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] under a constant applied voltage, consistent with previous reports on CNT-filled PVDF systems [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] and general nanocomposite processing [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFurther increasing the CNT content to 0.2%wt (sample 3-R-0.2%) resulted in the largest average diameter (1219.7\u0026thinsp;\u0026plusmn;\u0026thinsp;245.8 nm) and a wide diameter range (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec), suggesting that excessive viscosity and polymer chain entanglement hindered effective jet stretching. In contrast, at 0.5%wt CNT loading (sample 4-R-0.5%), the average diameter decreased markedly to 605.0\u0026thinsp;\u0026plusmn;\u0026thinsp;62.2 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). This reduction is attributed to the increased electrical conductivity of the solution, which enhanced the electrostatic stretching force acting on the polymer jet, overcoming viscous effects and producing finer fibers [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. This mechanism is in agreement with established electrospinning theories governing jet dynamics and fiber formation for piezoelectric polymers [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] and is consistent with observations in composite systems [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eA pronounced reduction in fiber diameter and dispersion was observed when a rotating collector was employed. Pure PVDF fibers subjected to mechanical stretching during collection exhibited a much smaller average diameter (\u0026asymp;\u0026thinsp;503 nm) and narrower distribution compared to randomly collected fibers (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). This trend is further enhanced by CNT incorporation. The mechanically stretched sample containing 0.05%wt MWCNT showed the smallest average diameter among all samples (\u0026asymp;\u0026thinsp;397 nm) with the highest uniformity and a dominant diameter range of 400\u0026ndash;600 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). The reduction in fiber diameter results from a synergistic electro-mechanical process. First, the incorporation of conductive CNTs increases the solution's charge-carrying capacity, enhancing the electrostatic stretching force exerted on the polymer jet during electrospinning [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Second, the tangential force imposed by the high-speed rotating collector applies an additional longitudinal mechanical stress, further elongating the jet before solidification [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The combined action of this enhanced electrostatic pull and direct mechanical drawing overcomes the solution's viscous resistance, leading to significant jet attenuation and the production of finer, oriented fibers. This interplay between electrical and mechanical parameters is a cornerstone of controlled electrospinning [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] and is an established strategy for fabricating high-performance, oriented piezoelectric nanofibers [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAt higher CNT contents (0.2 and 0.5%wt, samples 7-A-0.2% and 8-A-0.5%), the average diameter increased slightly compared to sample 6-A-0.05% (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec and d), which can be attributed to increased solution viscosity and partial CNT agglomeration. Nevertheless, these mechanically stretched fibers remained significantly thinner and more uniform than their randomly collected counterparts, highlighting the dominant role of collector-induced tensile force in controlling fiber morphology. Overall, the results demonstrate that nanofiber diameter and uniformity are governed by a balance between solution viscosity, electrical conductivity, and mechanical stretching during electrospinning [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], consistent with processing principles for PVDF composites [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. An optimal CNT content of 0.05%wt, combined with mechanical stretching during collection, yields the most uniform and finest nanofibers. This outcome is consistent with reports linking refined fiber morphology to improved flexibility and enhanced piezoelectric strain sensitivity in PVDF-based nanofibrous sensors [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e4.3. β-Phase Formation Induced by Electrospinning and CNT Nucleation (FT-IR and XRD correlation)\u003c/h2\u003e \u003cp\u003eThe crystalline structure and β-phase evolution of the electrospun PVDF/MWCNT nanofibrous composites were investigated using X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. As reported in previous studies, the electroactive β phase of PVDF is characterized by diffraction peaks appearing at 2θ\u0026thinsp;\u0026asymp;\u0026thinsp;20\u0026ndash;21\u0026deg;, corresponding to the (110)/(200) planes of the β crystalline phase [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], which is a standard identification method in the literature [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. In the present study, all samples exhibited a dominant diffraction peak in this region, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, confirming the formation of the β phase in electrospun nanofibers.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAlthough the presence of a single dominant peak limited phase identification, variations in peak intensity provided valuable insight into changes in crystallinity and molecular orientation. According to the XRD intensity data summarized in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, samples containing 0.05%wt MWCNT (samples 2-R-0.05% and 6-A-0.05%) exhibited significantly higher peak intensities compared to other compositions. In particular, the mechanically stretched sample with 0.05%wt MWCNT showed the highest intensity among all samples, indicating enhanced crystalline ordering and β-phase development. This observation is consistent with earlier reports that electrospinning-induced jet stretching and collector-induced tensile forces promote molecular chain alignment and dipole orientation along the fiber axis [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. The observed β-phase enhancement at 0.05%wt MWCNT is attributed to the electrostatic interaction between the electronegative fluorine atoms in PVDF's CF₂ dipoles and the π-electron cloud of the CNTs, which templates the all-trans (TTTT) chain conformation and is consistent with self-polarization mechanisms reported for electrospun PVDF under strong elongational and electric fields [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eXRD peak intensity of electrospun PVDF/MWCNT nanofibers with different MWCNT loadings and collection conditions\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample Code\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2θ (\u0026deg;)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eIntensity (a.u.)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1-R-0%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e632.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2-R-0.05%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20.64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1848.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3-R-0.2%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e785.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4-R-0.5%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1276.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5-A-0%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1524.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6-A-0.05%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20.54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2076.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7-A-0.2%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1134.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8-A-0.5%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20.79\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1467.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn contrast, samples containing 0.2%wt MWCNT exhibited reduced XRD peak intensity, suggesting suppression of effective β-phase formation. As discussed in the Introduction, this behavior can be attributed to increased solution viscosity and insufficient elongational force acting on the polymer jet, which limits chain alignment during electrospinning. A partial recovery of peak intensity was observed at 0.5%wt MWCNT, indicating that CNTs can still contribute to nucleation; however, the effect was less pronounced due to the onset of CNT agglomeration, in agreement with reports on CNT-filled PVDF systems [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. This agglomeration behavior at higher loadings is a well-known challenge in nanotube composite processing [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The FT-IR spectra of samples are presented in Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e and \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, respectively. The calculated β-phase fraction, summarized in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, showed good overall agreement with the XRD trends. Notably, the mechanically stretched sample containing 0.05%wt MWCNT exhibited the highest relative β-phase fraction (~\u0026thinsp;78.5%), as estimated from FT-IR peak-area analysis.\u003c/p\u003e \u003cp\u003eMinor inconsistencies between XRD peak intensity and FT-IR-derived β-phase percentages were observed for certain samples, particularly at higher CNT contents. These discrepancies were attributed to limitations in peak intensity analysis and experimental uncertainties in FT-IR measurements. To address this issue, the area under the FT-IR absorption curves was calculated for selected samples (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), which confirmed that mechanically stretched samples consistently exhibited higher β-phase content than randomly collected ones. This result reinforces the conclusion that additional mechanical tension imposed by the rotating collector plays a decisive role in promoting β-phase formation, as previously reported in oriented electrospun PVDF systems [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] and supported by analyses of electrospinning-processing relationships [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eRelative β-phase fraction (F(β)) estimated from FT-IR peak-area analysis of the α-phase (763 cm⁻\u0026sup1;) and β-phase (840 cm⁻\u0026sup1;) absorption bands for electrospun PVDF/MWCNT nanofibers\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample Code\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF(β) (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1-R-0%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e68\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2-R-0.05%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e71\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3-R-0.2%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e69\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4-R-0.5%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e74.54\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5-A-0%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e72\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6-A-0.05%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e78.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7-A-0.2%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e75\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8-A-0.5%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e72\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eIntegrated area of the β-phase FT-IR absorption band (~\u0026thinsp;840 cm⁻\u0026sup1;) for selected PVDF/MWCNT samples, confirming enhanced β-phase content in mechanically stretched nanofibers\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample Code\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePeak Area (cm⁻\u0026sup1;) in 815\u0026ndash;850\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4-R-0.05%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e416.06\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7-A-0.2%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e431.43\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8-A-0.5%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e473.47\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eOverall, the combined XRD and FT-IR analyses demonstrate that CNTs act as effective nucleating agents up to an optimal concentration of 0.05%wt, facilitating α-to-β phase transformation through electrostatic interactions between CF₂ dipoles of PVDF chains and the π-electron system of CNTs. Beyond this concentration, CNT agglomeration driven by van der Waals and π\u0026ndash;π interactions reduces effective nucleation and limits further β-phase enhancement. These findings are in close agreement with the mechanisms proposed in the literature and provide a clear structure\u0026ndash;processing\u0026ndash;crystallinity relationship for electrospun PVDF/MWCNT nanofibrous composites.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e4.4. Mechanical Properties of PVDF/MWCNT Nanofibrous Composites\u003c/h2\u003e \u003cdiv id=\"Sec18\" class=\"Section3\"\u003e \u003ch2\u003e4.4.1. Stress\u0026ndash;Strain Behavior of PVDF/MWCNT Nanofibrous Mats\u003c/h2\u003e \u003cp\u003eThe tensile stress\u0026ndash;strain behavior of the electrospun PVDF/MWCNT nanofibrous composites was investigated to evaluate the intrinsic mechanical response of the materials under uniaxial loading. Representative stress\u0026ndash;strain curves for selected samples are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. For CNT-free samples, the randomly oriented PVDF nanofibers exhibited relatively low tensile strength and limited load-bearing capability, with a maximum stress of approximately 8 MPa. In contrast, the mechanically stretched PVDF nanofibers showed a substantially higher tensile strength (~\u0026thinsp;16.7 MPa), indicating more efficient load transfer along the fiber axis.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe incorporation of MWCNTs at low loading levels led to a pronounced enhancement in tensile strength. In particular, samples containing 0.05%wt MWCNT exhibited the highest stress values, reaching approximately 16.94 MPa for randomly collected fibers and 20.21 MPa for mechanically stretched fibers. This improvement can be attributed to the combined effects of CNT-induced reinforcement, improved interfacial interactions, and increased β-phase content, as discussed in Section \u003cspan refid=\"Sec15\" class=\"InternalRef\"\u003e4.2\u003c/span\u003e. The higher β-phase fraction, which is associated with increased chain rigidity and dipole alignment, contributes to the enhanced stiffness and strength of the nanofibrous mats.\u003c/p\u003e \u003cp\u003eAt higher CNT contents (0.2% and 0.5%wt), a gradual decrease in tensile strength was observed, particularly for randomly oriented samples. This reduction is attributed to CNT agglomeration and increased solution viscosity, which leads to defects in fiber structure and reduced effective stress transfer. However, these samples generally exhibited higher elongation at break, indicating increased flexibility and ductility under tensile loading.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section3\"\u003e \u003ch2\u003e4.4.2. Comparison Between Randomly Collected and Mechanically Stretched Nanofibers\u003c/h2\u003e \u003cp\u003eA direct comparison between randomly collected and mechanically stretched nanofibrous mats highlights the critical role of collector-induced orientation in determining mechanical performance. For all CNT contents, mechanically stretched nanofibers consistently exhibited higher tensile strength and improved mechanical stability compared to their randomly collected counterparts (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e). This behavior is attributed to the additional mechanical stretching imposed by the rotating collector during electrospinning, which promotes molecular chain orientation, reduces fiber waviness, and enhances stress transfer efficiency.\u003c/p\u003e \u003cp\u003eThe superiority of mechanically stretched fibers was most pronounced at the optimal CNT content of 0.05wt%, where the combined effects of stretch-induced orientation and CNT-induced nucleation resulted in the highest tensile strength and most uniform stress\u0026ndash;strain response. These findings are consistent with previous studies reporting that oriented electrospun PVDF nanofibers exhibit enhanced mechanical robustness due to anisotropic reinforcement and improved molecular orientation\u0026mdash;a direct outcome of mechanical stretching during collection [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], as demonstrated in high-performance devices [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] and functional fabrics [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. This orientation maximizes the contribution of the high-modulus β-phase [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Even at higher CNT loadings, the mechanically stretched samples exhibited superior mechanical behavior compared to the randomly collected ones, underscoring the dominant influence of collector-induced mechanical stretching over compositional effects.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section3\"\u003e \u003ch2\u003e4.4.3. Implications of Mechanical Properties for Strain-Sensing Performance\u003c/h2\u003e \u003cp\u003eThe observed mechanical behavior has direct implications for the strain-sensing performance of the PVDF/MWCNT nanofibrous composites. Higher tensile strength and mechanical stability enable the nanofibrous mats to withstand repeated deformation without structural failure, which is essential for reliable strain sensing. Moreover, the enhanced β-phase content and improved chain orientation in mechanically robust samples facilitate more efficient electromechanical coupling under applied strain. In particular, the mechanically stretched PVDF/MWCNT nanofibers containing 0.05%wt CNT exhibited an optimal balance between strength, flexibility, and crystalline structure. This combination allows effective stress transfer to piezoelectric domains while maintaining sufficient deformability to generate measurable electrical signals. Consequently, the mechanical reinforcement achieved through controlled CNT loading and collector-imposed mechanical stretching plays a crucial role in enhancing strain sensitivity, supporting the structure\u0026ndash;property\u0026ndash;performance relationship discussed in subsequent sections.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e4.5. Piezoelectric Output and Strain Sensitivity\u003c/h2\u003e \u003cdiv id=\"Sec22\" class=\"Section3\"\u003e \u003ch2\u003e4.5.1. Dynamic Voltage Output and Sensitivity Analysis\u003c/h2\u003e \u003cp\u003eThe piezoelectric output and strain-sensing performance of the electrospun PVDF/MWCNT nanofibrous composites were evaluated under controlled dynamic mechanical excitation. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e presents the time-dependent output voltage signals of samples with different CNT contents and collection conditions (random vs. mechanically stretched). All measurements were conducted under identical excitation conditions (applied force of 2.65 N and frequency of 5 Hz), enabling direct comparison.\u003c/p\u003e \u003cp\u003ePure PVDF nanofibers (sample 1-R-0%) generated a relatively low output voltage (~\u0026thinsp;3.0 mV), reflecting limited piezoelectric activity due to the lower β-phase content discussed in Section \u003cspan refid=\"Sec16\" class=\"InternalRef\"\u003e4.3\u003c/span\u003e. A significant enhancement was observed upon MWCNT incorporation. The randomly collected sample containing 0.05wt% MWCNT (sample 2-R-0.05%) exhibited a maximum output voltage of approximately 3.93 mV, while the corresponding mechanically stretched sample (sample 6-A-0.05%) produced the highest output voltage of about 4.90 mV (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e). These results indicate that both CNT incorporation and mechanical stretching during collection contribute synergistically to improved piezoelectric performance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe strain sensitivity, defined as the ratio of output voltage to applied force (mV\u0026middot;N⁻\u0026sup1;), was calculated for all samples and is summarized in Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The highest sensitivity values were obtained for samples containing 0.05wt% MWCNT, reaching 1.48 mV\u0026middot;N⁻\u0026sup1; for the randomly collected sample and 1.84 mV\u0026middot;N⁻\u0026sup1; for the mechanically stretched sample. This trend mirrors the β-phase formation behavior identified in Section \u003cspan refid=\"Sec16\" class=\"InternalRef\"\u003e4.3\u003c/span\u003e, providing an initial indication that the piezoelectric output is strongly governed by crystalline structure.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eOutput voltage and strain sensitivity of electrospun PVDF/MWCNT nanofibrous sensors measured under a constant applied force of 2.65 N and excitation frequency of 5 Hz\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample Code\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOutput Voltage\u003c/p\u003e \u003cp\u003e(mV)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSensitivity\u003c/p\u003e \u003cp\u003e(mV\u0026middot;N⁻\u0026sup1;)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1-R-0%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2-R-0.05%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.48\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3-R-0.2%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.16\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4-R-0.5%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5-A-0%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.41\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6-A-0.05%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.84\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7-A-0.2%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8-A-0.5%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.35\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAt higher CNT contents (0.2 and 0.5wt%), a reduction in output voltage and sensitivity was observed for both randomly collected and mechanically stretched samples. Comparison between the two collection methods reveals that mechanically stretched samples consistently exhibit higher output voltage and sensitivity at identical CNT contents. The mechanically stretched PVDF/MWCNT nanofibers containing 0.05wt% CNT therefore demonstrate an optimal balance, yielding the highest absolute performance.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e \u003ch2\u003e4.5.2. Structure\u0026ndash;Property\u0026ndash;Performance Relationship\u003c/h2\u003e \u003cp\u003eThe experimental results demonstrate a clear and consistent relationship between processing parameters, material structure, and final piezoelectric performance. This relationship explains the optimal performance observed for the mechanically stretched 0.05wt% MWCNT sample (6-A-0.05%).\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eCrystalline Structure as the Foundation\u003c/strong\u003e \u003cp\u003eAs confirmed by XRD and FT-IR (Section \u003cspan refid=\"Sec16\" class=\"InternalRef\"\u003e4.3\u003c/span\u003e), electrospinning promotes β-phase formation in PVDF, while low loadings of MWCNTs (\u0026le;\u0026thinsp;0.05wt%) act as effective nucleating agents. The combination of mechanical stretching during collection and optimal CNT loading produced the highest β-phase fraction (~\u0026thinsp;78.5%) and crystalline orientation. This enhanced polar phase content is the primary determinant of piezoelectric response, as the generated surface charge is directly proportional to the density of aligned dipoles within the material.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eMechanical Robustness Enables Efficient Coupling\u003c/strong\u003e \u003cp\u003eMechanical testing (Section \u003cspan refid=\"Sec17\" class=\"InternalRef\"\u003e4.4\u003c/span\u003e) revealed a strong correlation between β-phase content and tensile performance. The mechanically stretched 0.05wt% CNT sample exhibited the highest tensile strength (~\u0026thinsp;20.21 MPa), indicating efficient load transfer and structural integrity resulting from molecular orientation. This mechanical robustness is critical for a strain sensor; it allows the nanofibrous mat to withstand repeated deformation and ensures efficient transfer of applied stress to the piezoelectric crystalline domains, minimizing energy loss to viscoelastic dissipation.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eThe Dual Role of CNTs and the Percolation Limit\u003c/strong\u003e \u003cp\u003eCarbon nanotubes play a dual role. At the optimal concentration (0.05wt%), they act as nucleating agents for the β-phase [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] and form localized conductive pathways that facilitate charge collection without reaching full electrical percolation [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The electrical conductivity of this optimal sample (~\u0026thinsp;10⁻⁷ S\u0026middot;m⁻\u0026sup1;) falls within a range that enhances signal output without short-circuiting the piezoelectric potential [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. At higher CNT contents (\u0026ge;\u0026thinsp;0.2wt%), agglomeration (as seen in SEM analysis, Section \u003cspan refid=\"Sec15\" class=\"InternalRef\"\u003e4.2\u003c/span\u003e) disrupts this synergy. Agglomerates act as defects that hinder stress transfer, reduce effective nucleation sites, and can create charge leakage pathways, leading to increased dielectric losses and diminished piezoelectric voltage output despite higher bulk conductivity [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eThe Critical Role of Mechanical Stretching\u003c/strong\u003e \u003cp\u003eThe superior performance of mechanically stretched fibers, even at identical CNT loadings, is attributed to the collector-imposed tensile force. This stretching refines fiber morphology (Section \u003cspan refid=\"Sec15\" class=\"InternalRef\"\u003e4.2\u003c/span\u003e), enhances molecular chain and dipole alignment along the fiber axis [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], and improves the mechanical properties necessary for durable sensing (Section \u003cspan refid=\"Sec17\" class=\"InternalRef\"\u003e4.4\u003c/span\u003e). This alignment maximizes the projection of the applied stress onto the polar axis of the β-phase crystals, leading to more efficient electromechanical conversion.\u003c/p\u003e \u003c/p\u003e \u003cp\u003eIn summary, the peak strain sensitivity of the stretched PVDF/MWCNT (0.05wt%) nanofibers is not the result of a single factor, but the synergistic outcome of a processing-structure-property triad: mechanical stretching induces optimal morphology and β-phase orientation, which is further nucleated and stabilized by well-dispersed CNTs. This structure simultaneously provides the high piezoelectric activity, mechanical durability, and balanced electrical conductivity required for a high-performance, flexible strain sensor.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"5. Strain-Sensing Mechanism","content":"\u003cp\u003eThe strain-sensing behaviour of the electrospun PVDF/MWCNT nanofibrous composites arises from the combined effects of intrinsic piezoelectricity and CNT-assisted electromechanical charge transport. Under applied mechanical deformation, the oriented β-phase dipoles in PVDF generate polarization charges proportional to the applied strain, in accordance with linear piezoelectric theory. This mechanism dominates at low mechanical stresses, where the electrical output scales linearly with deformation, as observed in the voltage\u0026ndash;time responses (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e) and sensitivity values (Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eCarbon nanotubes play a dual role in this sensing mechanism. First, CNTs act as nucleating agents during electrospinning, promoting α-to-β phase transformation and increasing dipole density within the nanofibers [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Second, at optimized concentrations (0.05%wt), CNTs facilitate effective charge distribution and collection by forming localized conductive pathways without reaching full electrical percolation [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. This enhances signal stability and amplifies the measurable voltage output without short-circuiting the piezoelectric response, consistent with mechanisms proposed in previous PVDF/CNT studies [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eMechanical stretching during collection further amplifies the strain-sensing response by improving stress transfer efficiency and promoting molecular orientation, where dipole orientation is maximized [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Mechanically stretched nanofibers, therefore, exhibit higher and more stable output signals than randomly collected mats at identical CNT contents, as demonstrated by the superior performance of sample 6-A-0.05% compared to sample 2-R-0.05%. This enhanced response is consistent with earlier reports on oriented electrospun PVDF nanofibers for sensing applications [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], a principle leveraged in modern high-performance piezoelectric fabrics and composite fibers [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. At higher CNT loadings (\u0026gt;\u0026thinsp;0.05%wt), CNT agglomeration and increased dielectric losses reduce effective polarization and disrupt uniform stress transfer, leading to diminished piezoelectric output despite higher conductivity. This behaviour highlights the importance of operating below the percolation threshold to preserve the dominance of the piezoelectric mechanism over purely resistive effects. The sensing response is dominated by the piezoelectric effect, as measurements were performed under dynamic loading without DC bias.\u003c/p\u003e \u003cp\u003eIn summary, the strain-sensing mechanism in PVDF/MWCNT nanofibrous composites is governed by a synergistic interaction between electrospinning-induced β-phase polarization, CNT-assisted charge transport, and mechanical stretching-induced orientation. Optimizing these parameters enables high sensitivity, mechanical durability, and signal stability, making the developed nanofibrous composites promising candidates for flexible and wearable strain-sensing applications.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this study, PVDF/MWCNT nanofibrous composites were successfully fabricated via electrospinning to systematically investigate the synergistic effects of in-process mechanical stretching and CNT incorporation on piezoelectric strain sensitivity. The key findings are summarized as follows:\u003c/p\u003e \u003cp\u003eThrough comprehensive structural analysis (XRD, FT-IR), we established that electrospinning inherently promotes the electroactive β-phase in PVDF. The addition of low-loading MWCNTs (0.05wt%) further enhanced this transformation via nucleation, while the mechanical stretching imposed by a rotating collector (500 rpm) significantly improved molecular and dipole alignment. This combined effect yielded the highest relative β-phase fraction (~\u0026thinsp;78.5%) and crystalline orientation.\u003c/p\u003e \u003cp\u003eThe optimized crystalline structure directly translated to superior mechanical and electromechanical properties. The mechanically stretched composite with 0.05wt% CNT exhibited the highest tensile strength (~\u0026thinsp;20.21 MPa) and, under dynamic loading, generated a peak output voltage of ~\u0026thinsp;4.9 mV with a strain sensitivity of 1.84 mV\u0026middot;N⁻\u0026sup1;. This performance represents a clear processing\u0026ndash;structure\u0026ndash;property relationship: mechanical stretching refines morphology and orientation, while optimally dispersed CNTs nucleate the β-phase and facilitate charge collection without reaching electrical percolation.\u003c/p\u003e \u003cp\u003eThe results identify the optimal fabrication parameters as an 18wt% PVDF concentration, 0.05wt% MWCNT loading, and collection under moderate mechanical stretching (500 rpm). This approach provides a scalable and effective route to engineer flexible piezoelectric nanofibers. The resulting composites, which balance high sensitivity, durability, and flexibility, demonstrate strong potential for application in next-generation wearable electronics, structural health monitoring systems, and advanced human\u0026ndash;machine interfaces.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003cstrong\u003e:\u0026nbsp;\u003c/strong\u003eThe data used to support the findings of this study are included within the article.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical trial number:\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003cstrong\u003e:\u0026nbsp;\u003c/strong\u003eThe authors declare no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e There was no funding for this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contribution\u003c/strong\u003e\u003cstrong\u003e:\u0026nbsp;\u003c/strong\u003e\u003cu\u003eAtiyeh Amirhosseini:\u003c/u\u003e Methodology, Investigation, Writing \u0026ndash; original draft. \u003cu\u003eMahdi Nouri\u003c/u\u003e: Conceptualization, Supervision. \u003cu\u003eMostafa Jamshidi Avanaki\u003c/u\u003e: Supervision, Conceptualization, Methodology, Investigation, review \u0026amp; editing\u0026ndash;original draft. All authors discussed the results and commented on the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eSharma S, Mishra SS, Kumar R, Yadav RM (2022) Recent progress on polyvinylidene difluoride-based nanocomposites: applications in energy harvesting and sensing. New J Chem 46:18613-18646. https://doi.org/10.1039/D2NJ00002D\u003c/li\u003e\n\u003cli\u003eZhang H, Ji X, Wang Z, Tang S, Wang Z, Zhu W (2026) Advances in intelligent polyvinylidene fluoride-based piezoelectric composites for self-powered wearable electronics. Small 22:e09387. https://doi.org/10.1002/smll.202509387\u003c/li\u003e\n\u003cli\u003eRuan L, Yao X, Chang Y, Zhou L, Qin G, Zhang X (2018) Properties and applications of the \u0026beta; phase poly(vinylidene fluoride). Polymers 10:228. https://doi.org/10.3390/polym10030228\u003c/li\u003e\n\u003cli\u003eZhu J, Zhang X, Yang G, Su F, Ali S, Dai K, Liu C (2025) Nanofibrous PVDF-based smart flexible fabrics with high piezoelectric properties for human motion monitoring. ACS Appl Polym Mater 7:5501-5509. https://doi.org/10.1021/acsapm.5c00267\u003c/li\u003e\n\u003cli\u003eZhou S, Zhao Z, Wang Z, Yang L (2026) Hybrid piezo-triboelectric porous PVDF/CNT/PDMS pressure sensor enabling surface-defect and texture recognition. Int J Mod Phys B 40:2650033. https://doi.org/10.1142/S0217979226500335\u003c/li\u003e\n\u003cli\u003eHe Z, Rault F, Lewandowski M, Mohsenzadeh E, Sala\u0026uuml;n F (2021) Electrospun PVDF nanofibers for piezoelectric applications: A review of the influence of electrospinning parameters on the \u0026beta; phase and crystallinity enhancement. Polymers 13:174. https://doi.org/10.3390/polym13020174\u003c/li\u003e\n\u003cli\u003eLiu ZH, Pan CT, Lin LW, Lai HW (2013) Piezoelectric properties of PVDF/MWCNT nanofiber using near-field electrospinning. Sens Actuators A Phys 193:13-24. https://doi.org/10.1016/j.sna.2013.01.007\u003c/li\u003e\n\u003cli\u003eUtchimahali Muthu Raja P, Shenthilkumar RR, Kausalya Sasikumar G (2025) Structural optimization and piezoelectric performance of PVDF/MWCNT nanocomposites for wearable sensor applications. Microchem J 219:115841. https://doi.org/10.1016/j.microc.2025.115841\u003c/li\u003e\n\u003cli\u003eBai Y, Liu Y, Lv H, Shi H, Zhou W, Liu Y, Yu D-G (2022) Processes of electrospun polyvinylidene fluoride-based nanofibers, their piezoelectric properties, and several fantastic applications. Polymers 14:4311. https://doi.org/10.3390/polym14204311\u003c/li\u003e\n\u003cli\u003eYuan H, Zhou Q, Zhang Y (2025) Improving fibre alignment during electrospinning. In: Afshari M (ed) Electrospun nanofibers, 2nd edn. Elsevier, Amsterdam, pp 91-113. https://doi.org/10.1016/C2022-0-03204-9\u003c/li\u003e\n\u003cli\u003ePersano L, Dagdeviren C, Su Y, Zhang Y, Girardo S, Pisignano D, Huang Y, Rogers JA (2013) High performance piezoelectric devices based on aligned arrays of nanofibers of poly(vinylidenefluoride-co-trifluoroethylene). Nat Commun 4:1633. https://doi.org/10.1038/ncomms2639\u003c/li\u003e\n\u003cli\u003ePanditkar SS, Gurnule WB, Waghe PU, Gurnule PW, Kumar P (2026) The art and science of electrospinning: a detailed review of process and potential applications. Polym Bull 83:53. https://doi.org/10.1007/s00289-025-06071-0\u003c/li\u003e\n\u003cli\u003eHuang YY, Terentjev EM (2012) Dispersion of carbon nanotubes: mixing, sonication, stabilization, and composite properties. Polymers 4:275-295. https://doi.org/10.3390/polym4010275\u003c/li\u003e\n\u003cli\u003eKalimuldina G, Turdakyn N, Abay I, Medeubayev A, Nurpeissova A, Adair D, Bakenov Z (2020) A review of piezoelectric PVDF film by electrospinning and its applications. Sensors 20:5214. https://doi.org/10.3390/s20185214\u003c/li\u003e\n\u003cli\u003eYu H, Huang T, Lu M, Mao M, Zhang Q, Wang H (2013) Enhanced power output of an electrospun PVDF/MWCNTs-based nanogenerator by tuning its conductivity. Nanotechnology 24:405401. https://doi.org/10.1088/0957-4484/24/40/405401\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymer-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jpol","sideBox":"Learn more about [Journal of Polymer Research](https://www.springer.com/journal/10965)","snPcode":"10965","submissionUrl":"https://www.editorialmanager.com/jpol/","title":"Journal of Polymer Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Electrospinning, PVDF/MWCNT nanocomposites, β-phase orientation, Piezoelectric strain sensor, Mechanical stretching, Structure-property relationship","lastPublishedDoi":"10.21203/rs.3.rs-8916823/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8916823/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eElectrospun poly(vinylidene fluoride) (PVDF)\u0026ndash;based nanofibrous composites have attracted considerable interest for flexible and wearable strain-sensing applications due to their intrinsic piezoelectricity, low density, and mechanical compliance. In this study, PVDF/multi-walled carbon nanotube (MWCNT) nanofibrous composites were fabricated via electrospinning to systematically investigate the combined effects of CNT loading and in-process mechanical stretching on morphology, crystalline structure evolution, mechanical properties, and piezoelectric strain sensitivity. MWCNT contents of 0.05, 0.2, and 0.5wt% were incorporated into PVDF solutions electrospun under fixed parameters, with nanofibers collected under random and mechanically stretched (using a rotating drum collector at 500 rpm) conditions. Structural and phase analyses (SEM, XRD, FT-IR) revealed that the synergistic action of jet stretching and CNT-induced nucleation significantly enhanced the content and dipole orientation of the electroactive β-phase, particularly at 0.05wt% CNT loading. Mechanical testing demonstrated that stretched nanofiber mats exhibited superior tensile strength and stability compared to random mats. Piezoelectric measurements under dynamic loading showed that the stretched PVDF/MWCNT nanofibers containing 0.05wt% CNT generated the highest output voltage (~\u0026thinsp;4.9 mV) and strain sensitivity (1.84 mV\u0026middot;N⁻\u0026sup1;). These results demonstrate a clear processing\u0026ndash;structure\u0026ndash;property relationship and identify optimal electrospinning conditions for high-performance, flexible PVDF-based strain sensors.\u003c/p\u003e","manuscriptTitle":"Enhanced Piezoelectric Strain Sensitivity in Electrospun PVDF/MWCNT Nanofibers via Moderate Mechanical Stretching and β-Phase Orientation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-06 19:47:28","doi":"10.21203/rs.3.rs-8916823/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2026-03-03T14:09:19+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-03-03T09:41:43+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Journal of Polymer Research","date":"2026-02-27T19:24:18+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-02-24T01:38:16+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Polymer Research","date":"2026-02-20T07:54:30+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymer-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jpol","sideBox":"Learn more about [Journal of Polymer Research](https://www.springer.com/journal/10965)","snPcode":"10965","submissionUrl":"https://www.editorialmanager.com/jpol/","title":"Journal of Polymer Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"b3db50c6-3bf3-45aa-a5b7-c4ffd0d81bda","owner":[],"postedDate":"March 6th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-07T10:40:35+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-06 19:47:28","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8916823","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8916823","identity":"rs-8916823","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}