Preparation of ZnO/PVA Flexible Piezoelectric Films for Sensing Dynamic-Static Superimposed Loads under Varying Temperatures

Preparation of ZnO/PVA Flexible Piezoelectric Films for Sensing Dynamic-Static Superimposed Loads under Varying Temperatures | 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 Article Preparation of ZnO/PVA Flexible Piezoelectric Films for Sensing Dynamic-Static Superimposed Loads under Varying Temperatures Shuaichao Chen, Jiajing Li, Wendong Yang, Wentao Rong This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7087929/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 27 Nov, 2025 Read the published version in Scientific Reports → Version 1 posted 10 You are reading this latest preprint version Abstract Flexible thin-film sensors exhibit considerable application potential in the structural health monitoring of bridges under complex traffic scenarios, owing to their capability of rapidly responding to dynamic loads, static loads, and dynamic-static coupled loads. In this study, following the evaporation crystallization method, ZnO/PVA was deposited on the substrate to form a 10-µm-thick film by adjusting the material ratio (m(ZnO):m(PVA) = 4:1) and solution environment (pH = 12). After cutting and packaging, the flexible piezoelectric film sensor was obtained. The sensing characteristics of the ZnO/PVA film sensor under quasi-static, vibratory, and coupled-force loads were analyzed using a dynamic data acquisition system, revealing excellent response feedback in detecting these three stress states. the sensitivity, linearity, and electrical output response time (at 25°C) were 1.33, 0.38, and 14.44 mV/N; 2.1, 5.1, and 5.3%; and 50, 5, and 8 ms, respectively. Temperature-dependent tests (10–60°C) demonstrated significant signal stability after implementing a curve-fitting compensation algorithm (R²=0.998). This temperature correction mechanism addresses the critical challenge of environmental fluctuations in practical bridge monitoring scenarios where static stresses and dynamic vibrations coexist. Physical sciences/Engineering Physical sciences/Materials science Physical sciences/Physics ZnO/PVA flexible film sensor Structural health monitoring Dynamic-static coupled loads Temperature response correction Piezoelectric properties Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 1. Introduction The sensor materials currently employed for structural health monitoring of large-scale infrastructure, such as bridges, tunnels, and dams, require significant improvement and enhancement 1 . Existing mainstream detection methods exhibit notable limitations. For instance, strain gauges with piezoresistive properties are capable of measuring structural deformation under quasi-static stress but fail to detect vibration-induced damage caused by dynamic loads. On the other hand, rigid piezoelectric ceramics, such as lead zirconate titanate 2 and quartz 3 , are effective in monitoring dynamic load variations. However, these rigid sensors are prone to deformation or even damage under quasi-static loads, which alters the charge distribution on their surfaces and ultimately leads to inaccurate monitoring results. Large-scale infrastructure often experiences simultaneous quasi-static and dynamic loads, and the structural damage caused by their coupling effect is both significant and challenging to detect using the aforementioned sensor types. The proposed sensor’s multimodal stress sensing positions it as a promising solution for next-generation smart infrastructure systems requiring accurate and reliable health assessment under complex operational conditions. In this study, we developed a ZnO/PVA flexible piezoelectric thin film sensor that demonstrates excellent adaptability for monitoring both quasi-static and dynamic loads 4 . Nano-zinc oxide (nano-ZnO) is an important semiconductor material whose performance relies on its specific crystal morphology and uniform crystal arrangement, exhibiting excellent photoelectric, thermoelectric, and piezoelectric properties 5 – 7 . These characteristics collectively determine the accuracy of ZnO films in sensing multiple load conditions in practical applications. However, as a nanomaterial, ZnO is highly susceptible to agglomeration, forming relatively large particles, which results in unsatisfactory piezoelectric performance under load 8 . The addition of polymers has been shown to effectively control ZnO's crystal structure and enhance its piezoelectric properties. For instance, Ponnamma et al. synthesized ZnO/polymer nanocomposites, achieving multiple crystal morphologies, including nanoparticles, nanoflowers, and nanorods 9 . Similarly, Esthappan et al. prepared ZnO/polypropylene nanocomposites by melt mixing with 0–5 wt% ZnO, significantly improving the mechanical properties, dynamic mechanical performance, and thermal stability of the composites 10 Zhu et al. developed cellulose-based ZnO flexible piezoelectric films using a hydrothermal method, demonstrating excellent signal responses to pressure generated by biological movements and outstanding sensitivity 11 . Polyvinyl alcohol (PVA), an environmentally friendly dispersant and binder with excellent biocompatibility, is widely used for modifying ZnO. Roy et al. evaluated the dielectric properties of PVA/ZnO nanocomposite films and found that they exhibit lossless behavior above 10⁶ Hz, indicating their potential for microwave applications. This research provides a theoretical basis for utilizing ZnO/PVA film sensors in detecting quasi-dynamic stress/strain signals 12 . Fernandes et al. synthesized ZnO nanoparticles with an average diameter of 25 nm using the sol-gel method and observed that the roughness of PVA films remained unchanged upon the addition of ZnO 13 . Loh et al. 14 prepared ZnO-PPS/PVA films and demonstrated that these films exhibit comparable dynamic strain sensitivity and piezoelectricity without requiring high-voltage poling or mechanical stretching, unlike PVDF-based films 15 . Although PVDF films are mainstream in flexible piezoelectric materials, their synthesis process is complex, and their piezoelectric coefficient is relatively low, making them less favorable compared to alternative materials. Collectively, these studies highlight that ZnO/polymer composites 16 have established an irreplaceable position among technologically essential materials due to their broad range of applications. Nevertheless, in engineering practices involving outdoor operations, temperature is a critical factor influencing the accuracy of sensor signal transmission. Ambient temperature exhibits significant variations throughout the year, with winter temperatures dropping below − 10°C and even reaching − 30°C or -40°C in high-latitude regions. Conversely, summer temperatures often exceed 35°C, with near-equatorial regions occasionally surpassing 40°C. Additionally, daily temperature fluctuations can be substantial. Such wide temperature ranges inevitably affect the electrical properties of nano-ZnO films 17 . Kumar et al. demonstrated that nanocomposite films incorporating zinc oxide nanostructures within a common paper matrix can serve as energy-conversion devices, transforming mechanical and thermal energy into electrical power 18 . This study represents an early exploration of the thermoelectric response of ZnO flexible films. To develop a ZnO flexible film sensor with high sensitivity, wide-frequency detection, simultaneous quasi-dynamic stress/strain signal monitoring, and perennial real-time operation capabilities, addressing external interferences such as thermal and light effects remains a significant challenge 19 . In light of this issue, this research investigates the electric response of ZnO/PVA flexible films to mechanical vibrations under varying temperature conditions. This study aims to develop a ZnO/PVA flexible piezoelectric thin film sensor capable of detecting the structural health of large-scale infrastructure, such as bridges and tunnels, under combined quasi-static and dynamic loading conditions at varying ambient temperatures. First, the ZnO/PVA ultrathin film was synthesized using a volatile crystallization technique, leveraging the high volatility of acetate and ammonium to form flower-shaped ZnO structures. Second, the sensing characteristics of the ZnO/PVA flexible film under quasi-static, vibrational, and superimposed loads were investigated by simulating these loading conditions and monitoring the corresponding electrical response signals. Third, the influence of ambient temperature variations on the sensor's output signals was corrected to enhance the accuracy and reliability of the ZnO/PVA flexible film sensor. 2. Experiment Details 2.1 Raw materials Zinc acetate (Zn(CH₃COO)₂, mass fraction ≥ 99%) and polyvinyl alcohol (PVA-1788) were purchased from Sinopharm Group Chemical Reagent Co., Ltd. (Shanghai, China). Ammonia (NH₃·H₂O, mass fraction = 25–28%) was obtained from Yantai Sanhe Reagent Co., Ltd. (Yantai, China). The zinc-based substrate used had a thickness of 400 µm, and ultrapure water prepared in the laboratory was utilized for all tests. 2.2 Synthesis of ZnO/PVA and film sensor fabrication The synthesis process of the ZnO/PVA film sensor is illustrated in Fig. 1 . First, 1 g of PVA was added to 60 mL of ultrapure water and stirred at 300 rad/min for 4 hours at 50°C. After standing for 24 hours, a PVA gel was obtained. Second, a Zn²⁺ ion solution was prepared by dissolving 1.83 g of Zn(CH₃COO)₂ in 100 mL of ultrapure water, assisted by ultrasonic dispersion until complete dissolution (KQ2200DB type, Kunshan Ultrasonic Instrument Co., Ltd., China). Third, ammonia was titrated into the Zn(CH₃COO)₂ solution until the turbidity disappeared, resulting in the formation of a Zn(OH)₄²⁻ sol. During the ammonia titration process, the pH value of the solution varied, which played a critical role in controlling the synthesis of ZnO. Fourth, 60 mL of the PVA gel was mixed into the Zn(OH)₄²⁻ sol under ultrasonic dispersion. Fifth, a polished zinc-based substrate was placed in a petri dish (d = 120 mm), and 10 mL of the sol-gel was added. Sixth, the petri dish was heated at 135°C for 24 hours to obtain the ZnO/PVA layer. Subsequently, the material was encapsulated into a flexible film sensor. An electrode made of aluminum foil was attached to the surface 20 , 21 , and wires were connected. The working area of the sensor measured 40 mm in length and 10 mm in width, with the ZnO/PVA layer having a thickness of approximately 10 µm. 2.3 Characterizations of ZnO/PVA layers The crystal structures, chemical changes, and microstructure of the ZnO/PVA film were characterized using powder X-ray diffraction (XRD, D8 Advance type, Bruker Ltd., Germany), thermogravimetric analysis/differential thermal analysis (TG/DTA, TAQ600, TA Instruments, Newcastle, Delaware), and scanning electron microscopy (SEM, S3500N type, Hitachi Corp., Japan). The XRD analysis was performed at a scanning rate of 0.25 °/s, with a 2θ range of 5° to 70° and a Cu Kα radiation wavelength of 0.1506 nm. The TG/DTA measurements were conducted from 25°C to 1000°C at a heating rate of 10°C/min under a nitrogen (N₂) atmosphere. 2.4 Characterizations of ZnO/PVA film sensors The test method for evaluating the electrical signal response performance of the ZnO/PVA flexible films is illustrated in Fig. 3 . A glass plate (30 mm × 100 mm × 600 mm) was fixed to the connecting rod of the base to form a cantilever beam. 2.4.1 Quasi-static stress response test The ZnO/PVA flexible film was adhered to the top surface of the cantilever beam, and a counterweight block (30 mm × 100 mm × 100 mm) was attached to the sensor. The quasi-static pressure response performance of the ZnO/PVA flexible films was evaluated by applying a specific pressure to the counterweight block and detecting the electrical signals transmitted by the sensor using a dynamic data acquisition system (DASP-v11 type, Orient Institute of Noise & Vibration, Beijing, China). 2.4.2 Vibratory load response test When an object is subjected to impact loads, inertial forces are generated, which reflect changes in the inherent properties of the bridge, such as elastic restoring forces and vibration frequencies. In this test, the counterweight block was removed, and the back of the glass plate was continuously struck with a hammer. The electrical signals transmitted by the sensor were monitored using the DASP-v11 system. 2.4.3 Coupled force response testing Coupled forces are generated when an object is subjected to both dynamic and static loads, reflecting changes in the properties of the bridge under traffic loads. In this experiment, the counterweight block was attached to the thin-film sensor, and the back of the glass plate was continuously struck with a hammer. The electrical signals transmitted by the sensor were monitored to evaluate its response. 2.4.4 Temperature response test The experimental setup shown in Fig. 3 a) was placed inside an electrothermal chamber. The temperature was sequentially calibrated to 22°C, 30°C, 38°C, 46°C, 60°C, and 70°C, with each temperature maintained for 60 minutes. Following the experimental protocol for the vibratory load response test, the sensing performance of the ZnO/PVA thin-film sensor was evaluated under these temperature conditions to comprehensively assess its performance characteristics and sensitivity within the specified temperature range. 3. Results 3.1. XRD Figure 4 illustrates the XRD patterns of the ZnO/PVA film at different pH values. Overall, the characteristic peaks of ZnO exhibited an increasing trend as the pH value increased, suggesting an improvement in the crystal structure of ZnO with higher pH values. At pH = 6 and pH = 8, the XRD patterns primarily displayed the characteristic peaks of metallic zinc. When the pH value reached 10, characteristic peaks of both zinc and ZnO were observed simultaneously. However, at pH = 14, the crystallinity of ZnO significantly declined. At pH = 12, the characteristic peaks of ZnO crystals closely matched those of standard crystals, as confirmed by the standard PDF cards (JCPDS 65-3411). The hexagonal wurtzite structure planes, including (100), (002), (101), (102), (110), (103), (112), and (201), corresponded well to the 2θ values at 31.2°, 35°, 36.3°, 47.5°, 57.5°, 62.5°, 68.4°, and 68.9°, respectively. These results indicate that the synthesized ZnO exhibits the optimal crystal structure at pH = 12. 3.2. TG/DTA Figure 5 presents the thermogravimetric curves of ZnO/PVA powder. The ZnO content in each ZnO/PVA powder sample, as shown in Fig. 5 a), was 100%, 90%, 80%, and 60%, respectively. The curve trend in Fig. 5 b) significantly differed from those in Fig. 5 c) to Fig. 5 e). When heated to 900°C, the mass loss rate decreased from 99.6–98.6%, representing a reduction of less than 1%. The heat flow curve exhibited only one absorption peak below 100°C, primarily attributed to the evaporation of free water adsorbed on the ZnO surface. The mass curves in Fig. 5 c) to Fig. 5 e) displayed three distinct weight loss stages: room temperature to 100°C, 150°C to 270°C, and 600°C to 900°C. The weight loss below 100°C was mainly caused by the volatilization and endothermic process of free water. In the second stage, three prominent endothermic peaks were observed at 150°C, 220°C, and 270°C, corresponding to the volatilization and endothermic process of polyvinyl alcohol (PVA) combined with water, the melting and endothermic process of PVA, and the dehydroxylation of PVA, respectively. The mass loss rates for the three ZnO/PVA compositions at this stage were 7.16%, 14.87%, and 27.1%, indicating that the mass loss rate increased with higher PVA content. As the temperature further increased to 350°C, a weak endothermic peak appeared, corresponding to the pyrolysis, cyclization, and carbonization reactions of PVA. The weight loss observed above 700°C was primarily associated with the chemical reduction of ZnO by carbon, where the carbon originated from PVA. Based on the principle of mass conservation, the mass ratio of ZnO to PVA was consistent with the design values. 3.3 SEM Figure 6 illustrates the microscopic morphology of the ZnO/PVA film sensor at various mass ratios. The particle morphology of pure ZnO exhibited a spear-like shape overall, with lengths ranging from approximately 500 nm to 1200 nm and a width of about 100 nm. However, significant agglomeration was observed. When the mass ratio of PVA to ZnO was 1:9, Fig. 6 b) clearly revealed multiple petal-like particles. These petals were composed of regularly shaped cylindrical structures joined together, with lengths ranging from 3000 nm to 6000 nm, significantly larger than those of pure ZnO. A small amount of precipitation was also observed on the particle surfaces. At a PVA-to-ZnO mass ratio of 2:8, the cylindrical morphology of ZnO/PVA became even more pronounced, with particle lengths of approximately 2000 nm and a substantial amount of flocculent precipitation on the surfaces. When the mass ratio of PVA to ZnO was 4:6, the particles displayed a unique flake-like morphology, adhering together with a thickness of about 100 nm and a width of around 400 nm. It can be concluded that as the PVA content increased, the length of ZnO/PVA particles initially increased and then decreased. Notably, when the PVA content ranged between 10% and 20%, the particles exhibited a distinct petal-like morphology. Figure 7 illustrates the detailed morphology of the ZnO/PVA fracture, revealing exposed hexagonal prisms and a complete bond between the ZnO and PVA interfaces. Figures 7 a) and 7b) depict the ZnO/PVA morphology with PVA contents of 10% and 20%, respectively. In these images, ZnO is located at the center, with a width of approximately 400 nm, while the outer layer consists of PVA with a thickness of about 160 nm. When the PVA content increased to 20%, the width of ZnO decreased to 250 nm, and the thickness of PVA increased to 204 nm. The thickness of PVA plays a critical role in the composite structure. On one hand, PVA envelops the ZnO surface, providing load-bearing capacity and preventing ZnO from scattering, thereby ensuring the stability of the ZnO/PVA thin film sensor. On the other hand, the PVA coating acts as an insulating layer on the surface of ZnO crystals, preventing electron pair annihilation and thereby maintaining the overall potential difference of the film. 3.4 Piezoelectric sensing performance of ZnO/PVA composite films under diverse loading conditions 3.4.1 Quasi-static stress response test Figure 8 illustrates the time-domain waveform diagrams of the hammering force and the corresponding electric voltage of the ZnO/PVA film sensor. The spectrum was subjected to five loading cycles, each lasting five seconds. The pressure loading path was clearly visible from the linear trend, with the peaks marked by yellow circles. After smoothing the vibration waveform and identifying the peaks, all peak electric signals responded accurately to the pressure loads. By magnifying the first loading process, it was found that the quasi-static pressure loading process can be mainly divided into three stages. Firstly, in the pressure application stage, the response signal increased with the rise of pressure and then reached a peak, with the peak response signal lagging by approximately 50 ms. After unloading, the response signal decreased as the load reduced, and the elastic deformation of the film gradually recovered. When the load was completely removed, the film produced aftershocks due to its own rigidity, and the response signal fluctuated. Figure 9 illustrates the response characteristics of the thin-film sensor to quasi-static loads, including response time, sensitivity, and linearity. In Fig. 9 a), the peak pressure times occurred at 958, 1982, 2959, 3984, and 4890 ms, respectively, while the corresponding response signal times were 1023, 2026, 3009, 4032, and 4933 ms. This indicates that the response hysteresis times of the ZnO/PVA thin-film sensor to the pressure load were 65, 44, 50, 48, and 43 ms, respectively. The average response time was approximately 50 ms, which aligns with the performance of traditional pressure sensors 22 , 23 . In Fig. 9 b), the slope of the curve was 1.33 mV/N. Given that the force-bearing area of the sensor was 4 × 10⁻⁴ m², the sensitivity of the thin-film sensor was calculated to be 13.3 mV/kPa. The linear fit was represented by the equation y = 1.33x + 141.57, with an R² value of 0.98, demonstrating that the ZnO/PVA thin-film sensor exhibits excellent response performance to quasi-static loads. 3.4.2 Vibratory load response test Figure 10 illustrates the vibration response spectrum of the sample, which was subjected to 12 impacts within 2.5 seconds. The curve differed from the relatively smooth linear trend observed in the quasi-static stress loading test. Instead, the electrical signals abruptly peaked after impacting the beam and then gradually decreased until reaching equilibrium. The underlying principle is as follows: when the beam was subjected to an impulse load, it experienced the greatest impact, resulting in the strongest electrical signal from the sensor. Subsequently, the beam's self-vibration attenuated over time, causing the electrical signal to diminish gradually. As shown in Fig. 11 , the response time of the ZnO/PVA thin-film sensor was 5 ms. The linear fit in Fig. 11 b) was represented by the equation y = 0.38x + 5.62, with an R² value of 0.99. The slope of the curve was 0.38 mV/N, indicating that the sensor exhibited excellent sensing performance for vibrations caused by impact loads. 3.4.3 Coupled force response test Figure 12 presents the signal response spectrum of the flexible thin-film sensor under superimposed loads. Figure 12 a) illustrates the vibration spectrum under nine impact loads applied within two seconds. The curve trend significantly differed from those observed in the previous two types of loading tests. The electrical signal of the sensor exhibited a wavy decay pattern. This phenomenon occurred because the vibration frequencies of the counterweight block and the cantilever beam differed after the sample was hammered, generating a coupling force. Over time, this force gradually declined, leading to the observed signal decay. Figure 12 b) displays the specific response of the ZnO/PVA film under coupled loading conditions. From the fitting curve, it is evident that the force generated by vibration exhibited periodic variation characteristics. The fitting equation was y = -265.6e⁻⁰·⁰⁶⁷ᵗ (t = 1, 2, …, 8), with a frequency of 62.5 Hz, indicating that the attenuation period of the coupling force was 0.016 s. This reflected that the vibration frequency of the small beam is 62.5 Hz. Once the specifications, synthesis process, and applicable conditions of the ZnO/PVA film sensor are confirmed, it can be widely utilized in detecting properties of different materials. In Fig. 13 , the response time and sensitivity of the sensor were 8 ms and 14.43 mV/N, respectively. The sensitivity was significantly higher than 1.34 mV/N of quasi-static loading test and 0.38 mV/N of dynamic loading test. The sensitivity under the coupled force was significantly higher than that under the quasi-static and dynamic loads, indicating that the coupling force was substantially greater than the other two types of loading modes. 3.5 Temperature-dependent piezoelectric sensing characteristics of ZnO/PVA composite films. In this study, considering that the ZnO/PVA thin-film sensor is designed for long-term outdoor structural health monitoring, its sensing performance under various temperature conditions was thoroughly investigated. Figure 14 illustrates the dot plots and fitting curves of the response signals of the ZnO/PVA thin-film sensor to vibration loads at different temperatures. The slope of the curves increased continuously with rising temperature, indicating that the electrical signal became more pronounced. The sensitivity values were 0.56 mV/N, 0.78 mV/N, 1.02 mV/N, 1.21 mV/N, and 1.64 mV/N at 22°C, 30°C, 38°C, 46°C, and 60°C, respectively. The R-squared values were all greater than 0.95, demonstrating a strong correlation. These results indicate that an increase in temperature enhances the sensitivity of the sensor. Figure 15 illustrates the dot plots and fitting curves of the response signals of the ZnO/PVA thin-film sensor to coupled loads at different temperatures. Contrary to the trend observed for vibratory loads, the slope of the curves decreased continuously as the temperature increased. The sensitivity values were 9 mV/N, 10.12 mV/N, 13.14 mV/N, 16.11 mV/N, 21.62 mV/N, and 25.42 mV/N at 22°C, 30°C, 38°C, 46°C, 60°C, and 70°C, respectively. The electrical response amplitude of the ZnO/PVA film increased with rising temperature. The correlation between the sensitivity results and temperature changes was analyzed, and the results are presented in Fig. 16 . The sensitivity was significantly influenced by temperature variations, exhibiting a linear relationship as described by the following equations: y = 0.03 x − 0.07 (Vibratory load Test) (3) y = 16.33–0.83 x + 0.03 x 2 -0.000193 x 3 (Coupled force Test) (4) The relationship between sensitivity and temperature demonstrated a first-order correlation in the vibratory load test and a third-order correlation in the coupled force test. The trends of the two curves were entirely distinct, primarily due to the fundamentally different loading mechanisms acting on the film sensor. From the perspective of molecular dynamics theory, the kinetic energy of the glass beam increased with rising temperature, enabling the ZnO/PVA film to continuously absorb additional energy and generate more pronounced electrical signals. Under impact loading, a vibration-coupling interaction occurred between the counterweight block and the beam element. As the temperature increased, the accumulation of kinetic energy led to a gradual enhancement in the signal intensity of the ZnO/PVA thin film. Consequently, the sensitivity exhibited a more significant upward trend. Therefore, it is essential to account for temperature in the electrical performance analysis of the ZnO/PVA film. By correcting the influence of temperature on sensor sensitivity, research on ZnO-based sensors can be made more meaningful. 4. Conclusions This study successfully synthesized ZnO/PVA composite crystals via evaporation crystallization, with systematic optimization of synthesis parameters characterized by XRD, thermogravimetric analysis, and SEM. (1) ZnO-to-PVA mass ratio 4:1 and pH 12 were optimal synthesis conditions, yielding flower-like monomers with superior crystallinity and uniform PVA encapsulation. These microstructures were subsequently deposited onto flexible substrates to fabricate ultrathin films (10 µm thickness) with tailored piezoresistive properties. (2) The ZnO/PVA film exhibited excellent mechanical response under three types loads. The sensitivity, linearity, and response time were 1.33, 0.38, and 14.44 mV/N; 2.1, 5.1, and 5.3%; and 50, 5, and 8 ms, respectively. (3) By correcting the temperature's effect on sensitivity, the accuracy of the sensor could effectively improve. These results highlight the ZnO/PVA film's potential for advanced applications in flexible pressure sensors, structural health monitoring systems high precision under dynamic-thermomechanical conditions. Declarations Author Contributions Shuaichao Chen, Jiajing Li, and Wentao Rong conceived and designed the experiments. Shuaichao Chen and Jiajing Li prepared the preliminary draft. Jiajing Li and Wendong Yang revised the manuscript and participated in discussions. Funding This work was supported by Science and Technology Plan of the Department of Transport of Shandong Province (Grant No. 2025B18) Data Availability Statement The data presented in this study are available on request from the corresponding author. Conflicts of Interest The authors declare no potential conflicts of interest regarding the commercial or financial relationships related to this research. Disclaimer/Publisher’s Note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. References Bertola, N. J., Henriques, G. & Brühwiler, E. Assessment of the information gain of several monitoring techniques for bridge structural examination. J. Civil Struct. Health Monit. 13 , 983–1001 (2023). Zhang, L., Wang, C., Huo, L. & Song, G. Health monitoring of cuplok scaffold joint connection using piezoceramic transducers and time reversal method. Smart Mater. Struct. 25 , 035010 (2016). Kanazawa, K. & Cho, N. J. 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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-7087929","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":489403980,"identity":"7a80708c-d41f-49ad-87b2-3dba86cfb162","order_by":0,"name":"Shuaichao Chen","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwElEQVRIiWNgGAWjYDACCTBpw2AAptmI15IG1MJMmpbDJGjhn9187OGPmvOJ2yXyDzB8KDsMFGkgYMmdY+nGPMduJ+6ckczAOOPcYaDIAfxaDCRyzKQZG27nbriRzMDM2wZ0oUQCIS353yR/NpyDaPlLnJYcNgnehgMQLYzEaJG4kWYmzXMsuX7DmccGB3vOpfNI3CCghX9G8jPJHzV2xgbHEx8++FFmLcc/g4AWFHAAiHlIUD8KRsEoGAWjABcAAMJHQfiQ4PEuAAAAAElFTkSuQmCC","orcid":"","institution":"Shandong Transport Vocational Collage","correspondingAuthor":true,"prefix":"","firstName":"Shuaichao","middleName":"","lastName":"Chen","suffix":""},{"id":489403981,"identity":"2ba55db0-8206-4a6e-b0bd-20179041714d","order_by":1,"name":"Jiajing Li","email":"","orcid":"","institution":"Weifang Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Jiajing","middleName":"","lastName":"Li","suffix":""},{"id":489403982,"identity":"49ecf09d-f66f-404c-8d65-421c7b5437bb","order_by":2,"name":"Wendong Yang","email":"","orcid":"","institution":"Shandong Transport Vocational Collage","correspondingAuthor":false,"prefix":"","firstName":"Wendong","middleName":"","lastName":"Yang","suffix":""},{"id":489403983,"identity":"00238a3c-a2c4-467b-8e0c-22c2bfd2f34c","order_by":3,"name":"Wentao Rong","email":"","orcid":"","institution":"Shandong Transport Vocational Collage","correspondingAuthor":false,"prefix":"","firstName":"Wentao","middleName":"","lastName":"Rong","suffix":""}],"badges":[],"createdAt":"2025-07-10 01:38:22","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7087929/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7087929/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-25644-7","type":"published","date":"2025-11-27T15:56:54+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":87439482,"identity":"1555f57a-94a2-42fd-a517-ff8042f68cb1","added_by":"auto","created_at":"2025-07-23 19:24:21","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":161594,"visible":true,"origin":"","legend":"\u003cp\u003eFabrication methodology for ZnO/PVA composite film sensors.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7087929/v1/d5c919194142a1e4cbb50157.png"},{"id":87440494,"identity":"50cce40d-50d5-481c-bb96-dd39a759733b","added_by":"auto","created_at":"2025-07-23 19:48:21","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":169089,"visible":true,"origin":"","legend":"\u003cp\u003eSide-angle SEM images of ZnO/PVA composite film at 1.6k magnification\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7087929/v1/fd933ee8a5e26e112605236c.png"},{"id":87439916,"identity":"3a1bdd9c-cf08-4b69-a475-61eb388e5b78","added_by":"auto","created_at":"2025-07-23 19:32:21","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":177744,"visible":true,"origin":"","legend":"\u003cp\u003eThe schematic setup includes: a) the fixture device and force application position, b) the dynamic data acquisition system for measuring the electric responses of flexible film sensors (① DASP-v11, ② hammer, ③ monitor, ④ sample), and c) the ZnO/PVA film.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7087929/v1/314f610b62a5b4b90b2b7b83.png"},{"id":87440739,"identity":"026e1a2e-aa3d-4b92-9ed6-9e397e6266f4","added_by":"auto","created_at":"2025-07-23 19:56:21","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":22969,"visible":true,"origin":"","legend":"\u003cp\u003ePhase crystallinity of ZnO/PVA powder at different pH values\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7087929/v1/eaf9af15453bca576da9e6bd.png"},{"id":87439487,"identity":"9136dfa1-498f-4633-ab77-a93db1772da0","added_by":"auto","created_at":"2025-07-23 19:24:21","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":30930,"visible":true,"origin":"","legend":"\u003cp\u003eThermogravimetric analysis of ZnO/PVA composites with varying mass ratios of ZnO to Polyvinyl alcohol\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7087929/v1/8584707cac2aa17408534e12.png"},{"id":87440741,"identity":"ac2b551e-0a25-4c09-83c3-de531378915c","added_by":"auto","created_at":"2025-07-23 19:56:21","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":326539,"visible":true,"origin":"","legend":"\u003cp\u003eSEM Images of ZnO/PVA films at different material Ratios: a) 100% ZnO; b) 90% ZnO and 10% PVA (×5k); c) 80% ZnO and 20% PVA (×13k); d) 60% ZnO and 40% PVA (×30k);\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7087929/v1/69263dac56e90231b9a57b86.png"},{"id":87439488,"identity":"c5dfb24f-5d0b-4931-a019-4af47cf2ba8c","added_by":"auto","created_at":"2025-07-23 19:24:21","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":294025,"visible":true,"origin":"","legend":"\u003cp\u003eSpecific morphology of ZnO/PVA composites: a) 90% ZnO and 10% PVA (×65k); b) 80% ZnO and 20% PVA (×75k); c) detailed morphology of ZnO/PVA (×23k); d) enlarged fracture morphology of ZnO/PVA (×85k)\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-7087929/v1/4d9018e4ed5dfc401596f3a5.png"},{"id":87439497,"identity":"f8626bb3-1e47-4db5-97df-42880965125c","added_by":"auto","created_at":"2025-07-23 19:24:21","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":115236,"visible":true,"origin":"","legend":"\u003cp\u003eVoltage response history of ZnO/PVA film sensor under quasi-static pressure load: a) Response voltage curve of ZnO/PVA film sensor and applied load curve; b) Detailed curve of the first loading stage.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-7087929/v1/77d38a182c30b3c35c410fe0.png"},{"id":87467143,"identity":"a5381d3d-3183-48e5-8d1e-128d90472971","added_by":"auto","created_at":"2025-07-24 08:01:04","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":20722,"visible":true,"origin":"","legend":"\u003cp\u003eFitting linear of a) peak pressure time and response signal time; b) peak pressure and response voltage signal\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-7087929/v1/52ae709e47b7d8a99ab18c23.png"},{"id":87440496,"identity":"4c733150-ecbb-4344-98d5-b0e554c8a411","added_by":"auto","created_at":"2025-07-23 19:48:21","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":50647,"visible":true,"origin":"","legend":"\u003cp\u003eElectric voltage response of ZnO/PVA composite film under impulse loading.\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-7087929/v1/ab24b87fe66072705b44e320.png"},{"id":87439499,"identity":"68de16bb-6a10-412c-b3d8-3485368f2996","added_by":"auto","created_at":"2025-07-23 19:24:21","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":24555,"visible":true,"origin":"","legend":"\u003cp\u003eLinear fitting analysis of a) impulse load peak time versus response signal time; b) impulse load peak amplitude versus response voltage signal.\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-7087929/v1/caaa342ea089e68bedbf7858.png"},{"id":87439920,"identity":"e7e4da14-947e-4236-a91c-0de9a4476ae4","added_by":"auto","created_at":"2025-07-23 19:32:21","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":39727,"visible":true,"origin":"","legend":"\u003cp\u003eVoltage response characteristics of ZnO/PVA composite film under coupled mechanical loading: a) correlation between applied load and sensor output voltage; b) detailed analysis of the secondary loading phase\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-7087929/v1/46115da0ba4385c3b350fccd.png"},{"id":87439927,"identity":"3960665a-fec7-4667-8205-1306c07e0f77","added_by":"auto","created_at":"2025-07-23 19:32:21","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":27654,"visible":true,"origin":"","legend":"\u003cp\u003eLinear correlation analysis of ZnO/PVA composite film performance: a) temporal relationship between peak voltage and impulse duration; b) dependence of peak voltage on applied impulse intensity\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-7087929/v1/cfcf08be1c30ea36a7caf21e.png"},{"id":87439513,"identity":"b8cba442-c564-4d10-b663-1601cc2b5c04","added_by":"auto","created_at":"2025-07-23 19:24:22","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":25860,"visible":true,"origin":"","legend":"\u003cp\u003eTemperature-dependent electromechanical response of piezoelectric materials to vibrational loading\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-7087929/v1/19275606d7c5eb9534860f4a.png"},{"id":87440379,"identity":"b2f39470-c0e9-4b3a-90cd-237d66eb5533","added_by":"auto","created_at":"2025-07-23 19:40:22","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":28877,"visible":true,"origin":"","legend":"\u003cp\u003eTemperature-dependent electrical response characteristics to coupled mechanical loading\u003c/p\u003e","description":"","filename":"15.png","url":"https://assets-eu.researchsquare.com/files/rs-7087929/v1/df26024fed8d91b0a22b46df.png"},{"id":87440378,"identity":"36fd073b-937e-48e4-9c88-870803f49534","added_by":"auto","created_at":"2025-07-23 19:40:21","extension":"png","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":20186,"visible":true,"origin":"","legend":"\u003cp\u003eTemperature-dependent sensitivity characteristics: experimental analysis and theoretical modeling\u003c/p\u003e","description":"","filename":"16.png","url":"https://assets-eu.researchsquare.com/files/rs-7087929/v1/47cd55e0f4a5f8d7edd3f7bc.png"},{"id":97179296,"identity":"7607d2cb-a5b4-4ffc-bc94-5db31ad7a6b7","added_by":"auto","created_at":"2025-12-01 16:14:31","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2424662,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7087929/v1/8dbc3dc6-cb68-4282-b5d4-28ee26439caa.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Preparation of ZnO/PVA Flexible Piezoelectric Films for Sensing Dynamic-Static Superimposed Loads under Varying Temperatures","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThe sensor materials currently employed for structural health monitoring of large-scale infrastructure, such as bridges, tunnels, and dams, require significant improvement and enhancement \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. Existing mainstream detection methods exhibit notable limitations. For instance, strain gauges with piezoresistive properties are capable of measuring structural deformation under quasi-static stress but fail to detect vibration-induced damage caused by dynamic loads. On the other hand, rigid piezoelectric ceramics, such as lead zirconate titanate \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e and quartz \u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e, are effective in monitoring dynamic load variations. However, these rigid sensors are prone to deformation or even damage under quasi-static loads, which alters the charge distribution on their surfaces and ultimately leads to inaccurate monitoring results. Large-scale infrastructure often experiences simultaneous quasi-static and dynamic loads, and the structural damage caused by their coupling effect is both significant and challenging to detect using the aforementioned sensor types. The proposed sensor\u0026rsquo;s multimodal stress sensing positions it as a promising solution for next-generation smart infrastructure systems requiring accurate and reliable health assessment under complex operational conditions. In this study, we developed a ZnO/PVA flexible piezoelectric thin film sensor that demonstrates excellent adaptability for monitoring both quasi-static and dynamic loads \u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eNano-zinc oxide (nano-ZnO) is an important semiconductor material whose performance relies on its specific crystal morphology and uniform crystal arrangement, exhibiting excellent photoelectric, thermoelectric, and piezoelectric properties \u003csup\u003e\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. These characteristics collectively determine the accuracy of ZnO films in sensing multiple load conditions in practical applications. However, as a nanomaterial, ZnO is highly susceptible to agglomeration, forming relatively large particles, which results in unsatisfactory piezoelectric performance under load \u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. The addition of polymers has been shown to effectively control ZnO's crystal structure and enhance its piezoelectric properties. For instance, Ponnamma et al. synthesized ZnO/polymer nanocomposites, achieving multiple crystal morphologies, including nanoparticles, nanoflowers, and nanorods \u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. Similarly, Esthappan et al. prepared ZnO/polypropylene nanocomposites by melt mixing with 0\u0026ndash;5 wt% ZnO, significantly improving the mechanical properties, dynamic mechanical performance, and thermal stability of the composites \u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e Zhu et al. developed cellulose-based ZnO flexible piezoelectric films using a hydrothermal method, demonstrating excellent signal responses to pressure generated by biological movements and outstanding sensitivity \u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003ePolyvinyl alcohol (PVA), an environmentally friendly dispersant and binder with excellent biocompatibility, is widely used for modifying ZnO. Roy et al. evaluated the dielectric properties of PVA/ZnO nanocomposite films and found that they exhibit lossless behavior above 10⁶ Hz, indicating their potential for microwave applications. This research provides a theoretical basis for utilizing ZnO/PVA film sensors in detecting quasi-dynamic stress/strain signals \u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. Fernandes et al. synthesized ZnO nanoparticles with an average diameter of 25 nm using the sol-gel method and observed that the roughness of PVA films remained unchanged upon the addition of ZnO \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. Loh et al. \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e prepared ZnO-PPS/PVA films and demonstrated that these films exhibit comparable dynamic strain sensitivity and piezoelectricity without requiring high-voltage poling or mechanical stretching, unlike PVDF-based films \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. Although PVDF films are mainstream in flexible piezoelectric materials, their synthesis process is complex, and their piezoelectric coefficient is relatively low, making them less favorable compared to alternative materials. Collectively, these studies highlight that ZnO/polymer composites \u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e have established an irreplaceable position among technologically essential materials due to their broad range of applications.\u003c/p\u003e\u003cp\u003eNevertheless, in engineering practices involving outdoor operations, temperature is a critical factor influencing the accuracy of sensor signal transmission. Ambient temperature exhibits significant variations throughout the year, with winter temperatures dropping below \u0026minus;\u0026thinsp;10\u0026deg;C and even reaching \u0026minus;\u0026thinsp;30\u0026deg;C or -40\u0026deg;C in high-latitude regions. Conversely, summer temperatures often exceed 35\u0026deg;C, with near-equatorial regions occasionally surpassing 40\u0026deg;C. Additionally, daily temperature fluctuations can be substantial. Such wide temperature ranges inevitably affect the electrical properties of nano-ZnO films \u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. Kumar et al. demonstrated that nanocomposite films incorporating zinc oxide nanostructures within a common paper matrix can serve as energy-conversion devices, transforming mechanical and thermal energy into electrical power \u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. This study represents an early exploration of the thermoelectric response of ZnO flexible films. To develop a ZnO flexible film sensor with high sensitivity, wide-frequency detection, simultaneous quasi-dynamic stress/strain signal monitoring, and perennial real-time operation capabilities, addressing external interferences such as thermal and light effects remains a significant challenge \u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. In light of this issue, this research investigates the electric response of ZnO/PVA flexible films to mechanical vibrations under varying temperature conditions.\u003c/p\u003e\u003cp\u003eThis study aims to develop a ZnO/PVA flexible piezoelectric thin film sensor capable of detecting the structural health of large-scale infrastructure, such as bridges and tunnels, under combined quasi-static and dynamic loading conditions at varying ambient temperatures. First, the ZnO/PVA ultrathin film was synthesized using a volatile crystallization technique, leveraging the high volatility of acetate and ammonium to form flower-shaped ZnO structures. Second, the sensing characteristics of the ZnO/PVA flexible film under quasi-static, vibrational, and superimposed loads were investigated by simulating these loading conditions and monitoring the corresponding electrical response signals. Third, the influence of ambient temperature variations on the sensor's output signals was corrected to enhance the accuracy and reliability of the ZnO/PVA flexible film sensor.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e"},{"header":"2. Experiment Details","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Raw materials\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eZinc acetate (Zn(CH₃COO)₂, mass fraction\u0026thinsp;\u0026ge;\u0026thinsp;99%) and polyvinyl alcohol (PVA-1788) were purchased from Sinopharm Group Chemical Reagent Co., Ltd. (Shanghai, China). Ammonia (NH₃\u0026middot;H₂O, mass fraction\u0026thinsp;=\u0026thinsp;25\u0026ndash;28%) was obtained from Yantai Sanhe Reagent Co., Ltd. (Yantai, China). The zinc-based substrate used had a thickness of 400 \u0026micro;m, and ultrapure water prepared in the laboratory was utilized for all tests.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Synthesis of ZnO/PVA and film sensor fabrication\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThe synthesis process of the ZnO/PVA film sensor is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. First, 1 g of PVA was added to 60 mL of ultrapure water and stirred at 300 rad/min for 4 hours at 50\u0026deg;C. After standing for 24 hours, a PVA gel was obtained. Second, a Zn\u0026sup2;⁺ ion solution was prepared by dissolving 1.83 g of Zn(CH₃COO)₂ in 100 mL of ultrapure water, assisted by ultrasonic dispersion until complete dissolution (KQ2200DB type, Kunshan Ultrasonic Instrument Co., Ltd., China). Third, ammonia was titrated into the Zn(CH₃COO)₂ solution until the turbidity disappeared, resulting in the formation of a Zn(OH)₄\u0026sup2;⁻ sol. During the ammonia titration process, the pH value of the solution varied, which played a critical role in controlling the synthesis of ZnO. Fourth, 60 mL of the PVA gel was mixed into the Zn(OH)₄\u0026sup2;⁻ sol under ultrasonic dispersion. Fifth, a polished zinc-based substrate was placed in a petri dish (d\u0026thinsp;=\u0026thinsp;120 mm), and 10 mL of the sol-gel was added. Sixth, the petri dish was heated at 135\u0026deg;C for 24 hours to obtain the ZnO/PVA layer.\u003c/p\u003e\u003cp\u003eSubsequently, the material was encapsulated into a flexible film sensor. An electrode made of aluminum foil was attached to the surface \u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e, and wires were connected. The working area of the sensor measured 40 mm in length and 10 mm in width, with the ZnO/PVA layer having a thickness of approximately 10 \u0026micro;m.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Characterizations of ZnO/PVA layers\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThe crystal structures, chemical changes, and microstructure of the ZnO/PVA film were characterized using powder X-ray diffraction (XRD, D8 Advance type, Bruker Ltd., Germany), thermogravimetric analysis/differential thermal analysis (TG/DTA, TAQ600, TA Instruments, Newcastle, Delaware), and scanning electron microscopy (SEM, S3500N type, Hitachi Corp., Japan). The XRD analysis was performed at a scanning rate of 0.25 \u0026deg;/s, with a 2θ range of 5\u0026deg; to 70\u0026deg; and a Cu Kα radiation wavelength of 0.1506 nm. The TG/DTA measurements were conducted from 25\u0026deg;C to 1000\u0026deg;C at a heating rate of 10\u0026deg;C/min under a nitrogen (N₂) atmosphere.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Characterizations of ZnO/PVA film sensors\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThe test method for evaluating the electrical signal response performance of the ZnO/PVA flexible films is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. A glass plate (30 mm \u0026times; 100 mm \u0026times; 600 mm) was fixed to the connecting rod of the base to form a cantilever beam.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\u003ch2\u003e2.4.1 Quasi-static stress response test\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThe ZnO/PVA flexible film was adhered to the top surface of the cantilever beam, and a counterweight block (30 mm \u0026times; 100 mm \u0026times; 100 mm) was attached to the sensor. The quasi-static pressure response performance of the ZnO/PVA flexible films was evaluated by applying a specific pressure to the counterweight block and detecting the electrical signals transmitted by the sensor using a dynamic data acquisition system (DASP-v11 type, Orient Institute of Noise \u0026amp; Vibration, Beijing, China).\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\u003ch2\u003e2.4.2 Vibratory load response test\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eWhen an object is subjected to impact loads, inertial forces are generated, which reflect changes in the inherent properties of the bridge, such as elastic restoring forces and vibration frequencies. In this test, the counterweight block was removed, and the back of the glass plate was continuously struck with a hammer. The electrical signals transmitted by the sensor were monitored using the DASP-v11 system.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\u003ch2\u003e2.4.3 Coupled force response testing\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eCoupled forces are generated when an object is subjected to both dynamic and static loads, reflecting changes in the properties of the bridge under traffic loads. In this experiment, the counterweight block was attached to the thin-film sensor, and the back of the glass plate was continuously struck with a hammer. The electrical signals transmitted by the sensor were monitored to evaluate its response.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\u003ch2\u003e2.4.4 Temperature response test\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThe experimental setup shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea) was placed inside an electrothermal chamber. The temperature was sequentially calibrated to 22\u0026deg;C, 30\u0026deg;C, 38\u0026deg;C, 46\u0026deg;C, 60\u0026deg;C, and 70\u0026deg;C, with each temperature maintained for 60 minutes. Following the experimental protocol for the vibratory load response test, the sensing performance of the ZnO/PVA thin-film sensor was evaluated under these temperature conditions to comprehensively assess its performance characteristics and sensitivity within the specified temperature range.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec12\"\u003e\n \u003ch2\u003e3.1. XRD\u003c/h2\u003e\n \u003cdiv\u003e\n \u003cp\u003eFigure \u003cspan\u003e4\u003c/span\u003e illustrates the XRD patterns of the ZnO/PVA film at different pH values. Overall, the characteristic peaks of ZnO exhibited an increasing trend as the pH value increased, suggesting an improvement in the crystal structure of ZnO with higher pH values. At pH\u0026thinsp;=\u0026thinsp;6 and pH\u0026thinsp;=\u0026thinsp;8, the XRD patterns primarily displayed the characteristic peaks of metallic zinc. When the pH value reached 10, characteristic peaks of both zinc and ZnO were observed simultaneously. However, at pH\u0026thinsp;=\u0026thinsp;14, the crystallinity of ZnO significantly declined. At pH\u0026thinsp;=\u0026thinsp;12, the characteristic peaks of ZnO crystals closely matched those of standard crystals, as confirmed by the standard PDF cards (JCPDS 65-3411). The hexagonal wurtzite structure planes, including (100), (002), (101), (102), (110), (103), (112), and (201), corresponded well to the 2\u0026theta; values at 31.2\u0026deg;, 35\u0026deg;, 36.3\u0026deg;, 47.5\u0026deg;, 57.5\u0026deg;, 62.5\u0026deg;, 68.4\u0026deg;, and 68.9\u0026deg;, respectively. These results indicate that the synthesized ZnO exhibits the optimal crystal structure at pH\u0026thinsp;=\u0026thinsp;12.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\"\u003e\n \u003ch2\u003e3.2. TG/DTA\u003c/h2\u003e\n \u003cdiv\u003e\n \u003cp\u003eFigure \u003cspan\u003e5\u003c/span\u003e presents the thermogravimetric curves of ZnO/PVA powder. The ZnO content in each ZnO/PVA powder sample, as shown in Fig. \u003cspan\u003e5\u003c/span\u003ea), was 100%, 90%, 80%, and 60%, respectively. The curve trend in Fig. \u003cspan\u003e5\u003c/span\u003eb) significantly differed from those in Fig. \u003cspan\u003e5\u003c/span\u003ec) to Fig. \u003cspan\u003e5\u003c/span\u003ee). When heated to 900\u0026deg;C, the mass loss rate decreased from 99.6\u0026ndash;98.6%, representing a reduction of less than 1%. The heat flow curve exhibited only one absorption peak below 100\u0026deg;C, primarily attributed to the evaporation of free water adsorbed on the ZnO surface.\u003c/p\u003e\n \u003cp\u003eThe mass curves in Fig. \u003cspan\u003e5\u003c/span\u003ec) to Fig. \u003cspan\u003e5\u003c/span\u003ee) displayed three distinct weight loss stages: room temperature to 100\u0026deg;C, 150\u0026deg;C to 270\u0026deg;C, and 600\u0026deg;C to 900\u0026deg;C. The weight loss below 100\u0026deg;C was mainly caused by the volatilization and endothermic process of free water. In the second stage, three prominent endothermic peaks were observed at 150\u0026deg;C, 220\u0026deg;C, and 270\u0026deg;C, corresponding to the volatilization and endothermic process of polyvinyl alcohol (PVA) combined with water, the melting and endothermic process of PVA, and the dehydroxylation of PVA, respectively. The mass loss rates for the three ZnO/PVA compositions at this stage were 7.16%, 14.87%, and 27.1%, indicating that the mass loss rate increased with higher PVA content. As the temperature further increased to 350\u0026deg;C, a weak endothermic peak appeared, corresponding to the pyrolysis, cyclization, and carbonization reactions of PVA. The weight loss observed above 700\u0026deg;C was primarily associated with the chemical reduction of ZnO by carbon, where the carbon originated from PVA. Based on the principle of mass conservation, the mass ratio of ZnO to PVA was consistent with the design values.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\"\u003e\n \u003ch2\u003e3.3 SEM\u003c/h2\u003e\n \u003cdiv\u003e\n \u003cp\u003eFigure \u003cspan\u003e6\u003c/span\u003e illustrates the microscopic morphology of the ZnO/PVA film sensor at various mass ratios. The particle morphology of pure ZnO exhibited a spear-like shape overall, with lengths ranging from approximately 500 nm to 1200 nm and a width of about 100 nm. However, significant agglomeration was observed. When the mass ratio of PVA to ZnO was 1:9, Fig. \u003cspan\u003e6\u003c/span\u003eb) clearly revealed multiple petal-like particles. These petals were composed of regularly shaped cylindrical structures joined together, with lengths ranging from 3000 nm to 6000 nm, significantly larger than those of pure ZnO. A small amount of precipitation was also observed on the particle surfaces. At a PVA-to-ZnO mass ratio of 2:8, the cylindrical morphology of ZnO/PVA became even more pronounced, with particle lengths of approximately 2000 nm and a substantial amount of flocculent precipitation on the surfaces. When the mass ratio of PVA to ZnO was 4:6, the particles displayed a unique flake-like morphology, adhering together with a thickness of about 100 nm and a width of around 400 nm. It can be concluded that as the PVA content increased, the length of ZnO/PVA particles initially increased and then decreased. Notably, when the PVA content ranged between 10% and 20%, the particles exhibited a distinct petal-like morphology.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eFigure \u003cspan\u003e7\u003c/span\u003e illustrates the detailed morphology of the ZnO/PVA fracture, revealing exposed hexagonal prisms and a complete bond between the ZnO and PVA interfaces. Figures \u003cspan\u003e7\u003c/span\u003ea) and 7b) depict the ZnO/PVA morphology with PVA contents of 10% and 20%, respectively. In these images, ZnO is located at the center, with a width of approximately 400 nm, while the outer layer consists of PVA with a thickness of about 160 nm. When the PVA content increased to 20%, the width of ZnO decreased to 250 nm, and the thickness of PVA increased to 204 nm. The thickness of PVA plays a critical role in the composite structure. On one hand, PVA envelops the ZnO surface, providing load-bearing capacity and preventing ZnO from scattering, thereby ensuring the stability of the ZnO/PVA thin film sensor. On the other hand, the PVA coating acts as an insulating layer on the surface of ZnO crystals, preventing electron pair annihilation and thereby maintaining the overall potential difference of the film.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\"\u003e\n \u003ch2\u003e3.4 Piezoelectric sensing performance of ZnO/PVA composite films under diverse loading conditions\u003c/h2\u003e\n \u003cdiv id=\"Sec16\"\u003e\n \u003ch2\u003e3.4.1 Quasi-static stress response test\u003c/h2\u003e\n \u003cdiv\u003e\n \u003cp\u003eFigure \u003cspan\u003e8\u003c/span\u003e illustrates the time-domain waveform diagrams of the hammering force and the corresponding electric voltage of the ZnO/PVA film sensor. The spectrum was subjected to five loading cycles, each lasting five seconds. The pressure loading path was clearly visible from the linear trend, with the peaks marked by yellow circles. After smoothing the vibration waveform and identifying the peaks, all peak electric signals responded accurately to the pressure loads. By magnifying the first loading process, it was found that the quasi-static pressure loading process can be mainly divided into three stages. Firstly, in the pressure application stage, the response signal increased with the rise of pressure and then reached a peak, with the peak response signal lagging by approximately 50 ms. After unloading, the response signal decreased as the load reduced, and the elastic deformation of the film gradually recovered. When the load was completely removed, the film produced aftershocks due to its own rigidity, and the response signal fluctuated.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eFigure \u003cspan\u003e9\u003c/span\u003e illustrates the response characteristics of the thin-film sensor to quasi-static loads, including response time, sensitivity, and linearity. In Fig. \u003cspan\u003e9\u003c/span\u003ea), the peak pressure times occurred at 958, 1982, 2959, 3984, and 4890 ms, respectively, while the corresponding response signal times were 1023, 2026, 3009, 4032, and 4933 ms. This indicates that the response hysteresis times of the ZnO/PVA thin-film sensor to the pressure load were 65, 44, 50, 48, and 43 ms, respectively. The average response time was approximately 50 ms, which aligns with the performance of traditional pressure sensors \u003csup\u003e\u003cspan\u003e22\u003c/span\u003e,\u003cspan\u003e23\u003c/span\u003e\u003c/sup\u003e. In Fig. \u003cspan\u003e9\u003c/span\u003eb), the slope of the curve was 1.33 mV/N. Given that the force-bearing area of the sensor was 4 \u0026times; 10⁻⁴ m\u0026sup2;, the sensitivity of the thin-film sensor was calculated to be 13.3 mV/kPa. The linear fit was represented by the equation y\u0026thinsp;=\u0026thinsp;1.33x\u0026thinsp;+\u0026thinsp;141.57, with an R\u0026sup2; value of 0.98, demonstrating that the ZnO/PVA thin-film sensor exhibits excellent response performance to quasi-static loads.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec17\"\u003e\n \u003ch2\u003e3.4.2 Vibratory load response test\u003c/h2\u003e\n \u003cdiv\u003e\n \u003cp\u003eFigure \u003cspan\u003e10\u003c/span\u003e illustrates the vibration response spectrum of the sample, which was subjected to 12 impacts within 2.5 seconds. The curve differed from the relatively smooth linear trend observed in the quasi-static stress loading test. Instead, the electrical signals abruptly peaked after impacting the beam and then gradually decreased until reaching equilibrium. The underlying principle is as follows: when the beam was subjected to an impulse load, it experienced the greatest impact, resulting in the strongest electrical signal from the sensor. Subsequently, the beam\u0026apos;s self-vibration attenuated over time, causing the electrical signal to diminish gradually. As shown in Fig. \u003cspan\u003e11\u003c/span\u003e, the response time of the ZnO/PVA thin-film sensor was 5 ms. The linear fit in Fig. \u003cspan\u003e11\u003c/span\u003eb) was represented by the equation y\u0026thinsp;=\u0026thinsp;0.38x\u0026thinsp;+\u0026thinsp;5.62, with an R\u0026sup2; value of 0.99. The slope of the curve was 0.38 mV/N, indicating that the sensor exhibited excellent sensing performance for vibrations caused by impact loads.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec18\"\u003e\n \u003ch2\u003e3.4.3 Coupled force response test\u003c/h2\u003e\n \u003cdiv\u003e\n \u003cp\u003eFigure \u003cspan\u003e12\u003c/span\u003e presents the signal response spectrum of the flexible thin-film sensor under superimposed loads. Figure \u003cspan\u003e12\u003c/span\u003ea) illustrates the vibration spectrum under nine impact loads applied within two seconds. The curve trend significantly differed from those observed in the previous two types of loading tests. The electrical signal of the sensor exhibited a wavy decay pattern. This phenomenon occurred because the vibration frequencies of the counterweight block and the cantilever beam differed after the sample was hammered, generating a coupling force. Over time, this force gradually declined, leading to the observed signal decay. Figure \u003cspan\u003e12\u003c/span\u003eb) displays the specific response of the ZnO/PVA film under coupled loading conditions. From the fitting curve, it is evident that the force generated by vibration exhibited periodic variation characteristics. The fitting equation was y = -265.6e⁻⁰\u0026middot;⁰⁶⁷ᵗ (t\u0026thinsp;=\u0026thinsp;1, 2, \u0026hellip;, 8), with a frequency of 62.5 Hz, indicating that the attenuation period of the coupling force was 0.016 s. This reflected that the vibration frequency of the small beam is 62.5 Hz. Once the specifications, synthesis process, and applicable conditions of the ZnO/PVA film sensor are confirmed, it can be widely utilized in detecting properties of different materials.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eIn Fig. \u003cspan\u003e13\u003c/span\u003e, the response time and sensitivity of the sensor were 8 ms and 14.43 mV/N, respectively. The sensitivity was significantly higher than 1.34 mV/N of quasi-static loading test and 0.38 mV/N of dynamic loading test. The sensitivity under the coupled force was significantly higher than that under the quasi-static and dynamic loads, indicating that the coupling force was substantially greater than the other two types of loading modes.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec19\"\u003e\n \u003ch2\u003e3.5 Temperature-dependent piezoelectric sensing characteristics of ZnO/PVA composite films.\u003c/h2\u003e\n \u003cdiv\u003e\n \u003cp\u003eIn this study, considering that the ZnO/PVA thin-film sensor is designed for long-term outdoor structural health monitoring, its sensing performance under various temperature conditions was thoroughly investigated.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan\u003e14\u003c/span\u003e illustrates the dot plots and fitting curves of the response signals of the ZnO/PVA thin-film sensor to vibration loads at different temperatures. The slope of the curves increased continuously with rising temperature, indicating that the electrical signal became more pronounced. The sensitivity values were 0.56 mV/N, 0.78 mV/N, 1.02 mV/N, 1.21 mV/N, and 1.64 mV/N at 22\u0026deg;C, 30\u0026deg;C, 38\u0026deg;C, 46\u0026deg;C, and 60\u0026deg;C, respectively. The R-squared values were all greater than 0.95, demonstrating a strong correlation. These results indicate that an increase in temperature enhances the sensitivity of the sensor.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eFigure \u003cspan\u003e15\u003c/span\u003e illustrates the dot plots and fitting curves of the response signals of the ZnO/PVA thin-film sensor to coupled loads at different temperatures. Contrary to the trend observed for vibratory loads, the slope of the curves decreased continuously as the temperature increased. The sensitivity values were 9 mV/N, 10.12 mV/N, 13.14 mV/N, 16.11 mV/N, 21.62 mV/N, and 25.42 mV/N at 22\u0026deg;C, 30\u0026deg;C, 38\u0026deg;C, 46\u0026deg;C, 60\u0026deg;C, and 70\u0026deg;C, respectively. The electrical response amplitude of the ZnO/PVA film increased with rising temperature.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eThe correlation between the sensitivity results and temperature changes was analyzed, and the results are presented in Fig.\u0026nbsp;\u003cspan\u003e16\u003c/span\u003e. The sensitivity was significantly influenced by temperature variations, exhibiting a linear relationship as described by the following equations:\u003c/p\u003e\n \u003cp\u003ey\u0026thinsp;=\u0026thinsp;0.03 x \u0026minus;\u0026thinsp;0.07 (Vibratory load Test) (3)\u003c/p\u003e\n \u003cp\u003ey\u0026thinsp;=\u0026thinsp;16.33\u0026ndash;0.83 x\u0026thinsp;+\u0026thinsp;0.03 x\u003csup\u003e\u003cspan\u003e2\u003c/span\u003e\u003c/sup\u003e -0.000193 x\u003csup\u003e\u003cspan\u003e3\u003c/span\u003e\u003c/sup\u003e (Coupled force Test) (4)\u003c/p\u003e\n \u003cp\u003eThe relationship between sensitivity and temperature demonstrated a first-order correlation in the vibratory load test and a third-order correlation in the coupled force test. The trends of the two curves were entirely distinct, primarily due to the fundamentally different loading mechanisms acting on the film sensor. From the perspective of molecular dynamics theory, the kinetic energy of the glass beam increased with rising temperature, enabling the ZnO/PVA film to continuously absorb additional energy and generate more pronounced electrical signals. Under impact loading, a vibration-coupling interaction occurred between the counterweight block and the beam element. As the temperature increased, the accumulation of kinetic energy led to a gradual enhancement in the signal intensity of the ZnO/PVA thin film. Consequently, the sensitivity exhibited a more significant upward trend. Therefore, it is essential to account for temperature in the electrical performance analysis of the ZnO/PVA film. By correcting the influence of temperature on sensor sensitivity, research on ZnO-based sensors can be made more meaningful.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThis study successfully synthesized ZnO/PVA composite crystals via evaporation crystallization, with systematic optimization of synthesis parameters characterized by XRD, thermogravimetric analysis, and SEM.\u003c/p\u003e\u003cp\u003e(1) ZnO-to-PVA mass ratio 4:1 and pH 12 were optimal synthesis conditions, yielding flower-like monomers with superior crystallinity and uniform PVA encapsulation. These microstructures were subsequently deposited onto flexible substrates to fabricate ultrathin films (10 \u0026micro;m thickness) with tailored piezoresistive properties.\u003c/p\u003e\u003cp\u003e(2) The ZnO/PVA film exhibited excellent mechanical response under three types loads. The sensitivity, linearity, and response time were 1.33, 0.38, and 14.44 mV/N; 2.1, 5.1, and 5.3%; and 50, 5, and 8 ms, respectively.\u003c/p\u003e\u003cp\u003e(3) By correcting the temperature's effect on sensitivity, the accuracy of the sensor could effectively improve. These results highlight the ZnO/PVA film's potential for advanced applications in flexible pressure sensors, structural health monitoring systems high precision under dynamic-thermomechanical conditions.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eShuaichao Chen, Jiajing Li, and Wentao Rong conceived and designed the experiments. Shuaichao Chen and Jiajing Li prepared the preliminary draft. Jiajing Li and Wendong Yang revised the manuscript and participated in discussions.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by Science and Technology Plan of the Department of Transport of Shandong Province (Grant No. 2025B18)\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data presented in this study are available on request from the corresponding author.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no potential conflicts of interest regarding the commercial or financial relationships related to this research.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDisclaimer/Publisher\u0026rsquo;s Note:\u003c/strong\u003e Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBertola, N. J., Henriques, G. \u0026amp; Br\u0026uuml;hwiler, E. Assessment of the information gain of several monitoring techniques for bridge structural examination. \u003cem\u003eJ. Civil Struct. Health Monit.\u003c/em\u003e \u003cb\u003e13\u003c/b\u003e, 983\u0026ndash;1001 (2023).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZhang, L., Wang, C., Huo, L. \u0026amp; Song, G. Health monitoring of cuplok scaffold joint connection using piezoceramic transducers and time reversal method. \u003cem\u003eSmart Mater. Struct.\u003c/em\u003e \u003cb\u003e25\u003c/b\u003e, 035010 (2016).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKanazawa, K. \u0026amp; Cho, N. J. Quartz crystal microbalance as a sensor to characterize macromolecular assembly dynamics. \u003cem\u003eJournal of Sensors\u003c/em\u003e 824947 (2009). (2009).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAbdeltwab, E. \u0026amp; Atta, A. 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Eng.\u003c/em\u003e \u003cb\u003e10\u003c/b\u003e, 17252\u0026ndash;17260 (2022).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"ZnO/PVA flexible film sensor, Structural health monitoring, Dynamic-static coupled loads, Temperature response correction, Piezoelectric properties","lastPublishedDoi":"10.21203/rs.3.rs-7087929/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7087929/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eFlexible thin-film sensors exhibit considerable application potential in the structural health monitoring of bridges under complex traffic scenarios, owing to their capability of rapidly responding to dynamic loads, static loads, and dynamic-static coupled loads. In this study, following the evaporation crystallization method, ZnO/PVA was deposited on the substrate to form a 10-µm-thick film by adjusting the material ratio (m(ZnO):m(PVA) = 4:1) and solution environment (pH = 12). After cutting and packaging, the flexible piezoelectric film sensor was obtained. The sensing characteristics of the ZnO/PVA film sensor under quasi-static, vibratory, and coupled-force loads were analyzed using a dynamic data acquisition system, revealing excellent response feedback in detecting these three stress states. the sensitivity, linearity, and electrical output response time (at 25°C) were 1.33, 0.38, and 14.44 mV/N; 2.1, 5.1, and 5.3%; and 50, 5, and 8 ms, respectively. Temperature-dependent tests (10–60°C) demonstrated significant signal stability after implementing a curve-fitting compensation algorithm (R²=0.998). This temperature correction mechanism addresses the critical challenge of environmental fluctuations in practical bridge monitoring scenarios where static stresses and dynamic vibrations coexist.\u003c/p\u003e","manuscriptTitle":"Preparation of ZnO/PVA Flexible Piezoelectric Films for Sensing Dynamic-Static Superimposed Loads under Varying Temperatures","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-23 19:24:16","doi":"10.21203/rs.3.rs-7087929/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-08-18T11:31:53+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-18T05:42:26+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"292367611450772379044565470171842760346","date":"2025-08-09T05:09:32+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-22T22:16:52+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"82992403568380623048819129689650078850","date":"2025-07-22T04:53:20+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-21T05:30:08+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-21T05:24:47+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-07-21T04:24:50+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-07-17T09:52:41+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-07-17T07:51:03+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"f2b0be4e-30f6-4d49-bddc-fa6460c1f15c","owner":[],"postedDate":"July 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":51956433,"name":"Physical sciences/Engineering"},{"id":51956434,"name":"Physical sciences/Materials science"},{"id":51956435,"name":"Physical sciences/Physics"}],"tags":[],"updatedAt":"2025-12-01T16:09:36+00:00","versionOfRecord":{"articleIdentity":"rs-7087929","link":"https://doi.org/10.1038/s41598-025-25644-7","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-11-27 15:56:54","publishedOnDateReadable":"November 27th, 2025"},"versionCreatedAt":"2025-07-23 19:24:16","video":"","vorDoi":"10.1038/s41598-025-25644-7","vorDoiUrl":"https://doi.org/10.1038/s41598-025-25644-7","workflowStages":[]},"version":"v1","identity":"rs-7087929","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7087929","identity":"rs-7087929","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}