PVA-Concentration-Regulated Conductive Inks for Low-Voltage-Driven Flexible Joule Heating Devices with Tunable Performance and Mechanical Robustness

PVA-Concentration-Regulated Conductive Inks for Low-Voltage-Driven Flexible Joule Heating Devices with Tunable Performance and Mechanical Robustness | 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 PVA-Concentration-Regulated Conductive Inks for Low-Voltage-Driven Flexible Joule Heating Devices with Tunable Performance and Mechanical Robustness Rongrong Yuan, Yizhe Sun, Xiuzhi Du, Lu Tao, Xinhui Cui, Zhipeng Li, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9105142/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Polyvinyl alcohol (PVA) concentration plays a key role in the printability, electrical conductivity, and electrothermal performance of conductive inks for flexible Joule heating devices. In this work, PEDOT:PSS/Cu@Ag composite inks with 5 wt%, 10 wt%, and 15 wt% PVA were prepared and systematically investigated. The viscosities of the three solutions were 454.09, 884.14, and 2917.01 mPa·s, respectively. Flexible devices were fabricated on polyimide substrates via doctor-blade printing and thermal curing. The 10 wt% PVA-based device exhibited the optimal performance, reaching 100°C at approximately 3 V. By designing single-line, series, and shunt electrode configurations, the shunt-connected device achieved the highest heating temperature of 110.7°C at 3 V. Bending tests demonstrated that the device maintained stable circuit continuity under a bending radius down to 2 mm at 3 V driving. This study provides an effective strategy for designing low-voltage-driven, mechanically robust flexible heating devices for wearable electronic applications. Conductive slurry Flexible devices Joule heating Polyvinyl Alcohol (PVA) Figures Figure 1 Figure 2 Figure 3 Figure 4 1. Introduction Flexible Joule heating devices have attracted significant attention for applications in wearable thermotherapy [ 1 – 5 ] and flexible electronics [ 6 – 10 ] , due to their lightweight, conformable nature, and efficient electrothermal conversion. Conductive inks, as the core material of these devices, must simultaneously satisfy requirements of high electrical conductivity, excellent mechanical flexibility, good printability, and low-voltage operation [ 11 – 16 ] . Polyvinyl alcohol (PVA) is a widely used polymer matrix for conductive inks due to its water solubility, biocompatibility, and good film-forming ability [ 17 – 20 ] . However, the concentration of PVA in the ink formulation plays a critical role in determining the final properties of the composite: low PVA concentrations may lead to poor film integrity and mechanical stability, while excessive PVA can form a thick insulating layer that hinders electron transport and reduces conductivity. Despite the importance of PVA concentration, a systematic study on its effect on the electrothermal performance of flexible heating devices is still lacking. Moreover, the scalability and performance tunability of these devices through electrode configuration (single-line, series, parallel) remain underexplored, and their mechanical robustness under extreme bending conditions is critical for practical applications. In this work, we address these gaps by systematically investigating the effect of PVA concentrations (5 wt%, 10 wt%, 15 wt%) on the properties of PEDOT:PSS/ Cu@Ag composite conductive inks. We fabricate flexible heating devices and evaluate their electrothermal performance, then explore electrode configuration as a strategy to tune performance. Finally, we assess the mechanical robustness of the optimized device under extreme bending conditions. Our results provide a clear understanding of the role of PVA concentration and electrode design in governing the performance of flexible Joule heating devices, offering a promising strategy for the design of high-performance flexible heating materials. 2. Experimental Section 2.1 Materials Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), polyvinyl alcohol (PVA, molecular weight ~ 89,000–98,000), Cu@Ag core–shell nanoparticles (10 wt% Ag content, average particle size 2–5 µm), glycerin (purity ≥ 99.5%), butylated hydroxytoluene (BHT), cellulose nanofibers (CNF), sodium dodecyl sulfate (SDS), and sodium alginate (SA) were used as received. The experimental substrate was ultra-thin polyimide (PI) film (thickness 0.025 mm). 2.2 Formulation Preparation Three conductive ink formulations were prepared with PVA concentrations of 5 wt%, 10 wt%, and 15 wt% as the polymer matrix. The detailed mass ratios of all components (PVA, PEDOT:PSS, Cu@Ag nanoparticles, glycerin, BHT, CNF, SDS, and SA) are listed in Table SI. Each ink was prepared via a two-step process: PVA powder was dissolved in deionized water at 90°C under magnetic stirring (300 rpm) for 1 h to form a homogeneous aqueous solution. The PVA solution was cooled to room temperature, and PEDOT:PSS, Cu@Ag nanoparticles, glycerin, BHT, CNF, SDS, and SA were added sequentially. The mixture was stirred at 300 rpm for 3 min, followed by ultrasonic dispersion (40 kHz, 300 W) for 5 min to break up agglomerates and ensure uniform dispersion of the conductive fillers. 2.3 Printing and Drying A stainless steel mask with custom patterns (line width: 2 mm, length: 20 mm, spacing: 5 mm) was clamped onto the PI substrate. The ink was coated using a stainless steel doctor blade (45°, 50 mm/s, controlled pressure: 10 N). After printing, the samples were dried in a convection oven with air circulation at 90°C for 15 min. The film thickness was controlled by the mask aperture (500 µm). For scalability tests, three electrode configurations (single-line, series, and shunt) were fabricated by adjusting the mask pattern. 2.4 Performance Characterization 2.4.1 Viscosity Measurement The viscosity of PVA solutions with different concentrations was measured using a rotational viscometer, with digital photographs of the measurement process shown in Supplementary Figure S2. 2.4.2 Electrothermal and Electrical Performance The electrothermal performance was characterized using a customized test platform consisting of a variable voltage source (0–30 V), a temperature sensor, and a laptop for data recording. Voltage-dependent temperature curves and maximum temperatures were obtained via infrared thermal imaging. 2.4.3 Mechanical Robustness Test The shunt-connected device was subjected to bending tests with radii of 20 mm, 10 mm, 5 mm, and 2 mm under a constant 3 V driving voltage. The device was connected in series with a green LED bead to visually confirm circuit continuity, and the current output was recorded under each bending condition. 2.4.4 Adhesion Test The adhesion of the ink film to the PI substrate was evaluated via a cross-hatch test following ASTM D3359. A multi-blade cutter was used to create a grid pattern, followed by application and removal of 3M tape (model 600-1PK). Adhesion grade was determined based on the ink shedding area, as specified in Table SII. 3. Results and Discussion 3.1 Fabrication and Characterization of Flexible Heating Devices The fabrication process of flexible Joule heating devices based on PVA-regulated conductive inks is illustrated in Fig. 1 . The two-step preparation method ensures uniform dispersion of conductive fillers in the PVA matrix: PVA powders of different concentrations are first dissolved to form aqueous solutions (Fig. 1 a(i)), then mixed with PEDOT:PSS, Cu@Ag nanoparticles, and functional additives (glycerin, BHT, CNF, SDS, SA) to prepare composite conductive inks (Fig. 1 a(ii)). The ink is then printed on PI substrates via mask-assisted doctor-blade coating, followed by thermal curing, cutting into designed wavy/linear patterns, and packaging with Ag paste, Cu wires, and PI tape to complete device assembly (Fig. 1 a(iii–v)). A customized electrothermal test platform (Fig. 1 c) was built to characterize device performance, and infrared thermal imaging (Fig. 1 b) confirmed the devices’ ability to generate uniform Joule heat, with maximum temperatures of 134°C and 104.2°C under 5 V and 3 V driving, respectively. The viscosity of the PVA solutions exhibited a significant concentration dependence: 454.09 mPa·s (5 wt% PVA), 884.14 mPa·s (10 wt% PVA), and 2917.01 mPa·s (15 wt% PVA) (Supplementary Figure S2). This viscosity variation directly impacts ink printability and film formation—low viscosity (5 wt% PVA) leads to poor film integrity, while excessively high viscosity (15 wt% PVA) hinders ink spreading and filler dispersion, laying the foundation for the divergent electrothermal performance of the three devices. 3.2 Effect of PVA Concentration on Electrothermal Performance The electrothermal conversion efficiency and electrical stability of devices with different PVA concentrations (No.1: 5 wt%, No.2: 10 wt%, No.3: 15 wt%) were systematically evaluated (Fig. 2 ). Infrared thermal images (Fig. 2 a) show distinct temperature distributions for each device at initial temperatures and under optimal driving voltages: No.2 (10 wt% PVA) reaches 104.2°C at 3 V, No.1 (5 wt% PVA) reaches 111.8°C at 5.5 V, and No.3 (15 wt% PVA) only reaches 98.3°C even at 8 V. Voltage-dependent temperature curves (Fig. 2 b) further quantify these differences: the No.2 device achieves the target temperature of 100°C at ~ 3 V, demonstrating the highest electrothermal conversion efficiency. In contrast, the No.1 device requires ~ 5.5 V to reach 100°C, and the No.3 device fails to attain this threshold even at the maximum tested voltage of 8 V. The underlying mechanism is revealed by the resistance–voltage characteristics (Fig. 2 c): the No.2 device maintains the lowest and most stable resistance across the entire voltage range, facilitating high current density and efficient Joule heat generation (Q = I²Rt). The No.1 device exhibits a gradual increase in resistance with voltage, likely due to poor film-forming ability of the low-concentration PVA matrix, which causes degradation of the conductive network under thermal stress. The No.3 device shows an extremely high initial resistance that decreases with increasing voltage, attributed to the excessive PVA forming a thick insulating layer that impedes electron transport; the resistance reduction at high voltages is likely due to thermal activation of charge carriers in the conductive fillers. These results confirm that 10 wt% PVA strikes an optimal balance between film-forming ability and electrical conductivity. 3.3 Tuning Electrothermal Performance via Electrode Configuration To further optimize the performance of the 10 wt% PVA-based ink, three electrode configurations (single-line, series-connected, shunt-connected) were fabricated and characterized (Fig. 3 ). Schematic diagrams of the three designs are shown in Fig. 3 a(i–iii): single-line, series-connected (1 + 2+3), and shunt-connected (1//2//3). The voltage-dependent electrothermal behavior of each configuration is presented in Fig. 3 b–d. The single-line device (Fig. 3 b) achieves a maximum temperature of 104.2°C at 3 V, with a symmetric temperature rise and fall with voltage variation, indicating stable low-voltage heating. The series-connected device (Fig. 3 c) requires a much higher voltage of 7.5 V to reach a comparable maximum temperature of 105.5°C, due to its increased total resistance limiting current density. The shunt-connected device (Fig. 3 d) outperforms the other two designs, attaining a maximum temperature of 110.7°C at 3 V, with a steeper temperature rise rate and superior electrothermal efficiency. Corresponding resistance characteristics (Fig. 3 e–g) elucidate the structural origin of these performance differences. The single-line device (Fig. 3 e) maintains a stable resistance of ~ 7–8 Ω across all sampling points, ensuring consistent current density. The series-connected device (Fig. 3 f) exhibits a significantly higher baseline resistance of ~ 16 Ω, directly explaining the need for elevated driving voltage. The shunt-connected device (Fig. 3 g) has a drastically reduced initial resistance of ~ 2 Ω, enabling a much higher current density under 3 V and thus enhanced Joule heating efficiency. These results demonstrate that electrode configuration is a facile and effective strategy to tune the electrothermal performance of flexible heating devices, with the shunt-connected design being optimal for low-voltage, high-temperature applications. 3.4 Mechanical Robustness under Extreme Bending The mechanical robustness and electrical stability of the optimized shunt-connected device were evaluated via bending tests under a constant 3 V driving voltage (Fig. 4 ). The device was connected in series with an LED bead to visually confirm circuit continuity, with tests conducted at bending radii of 20 mm, 10 mm, 5 mm, 2 mm, and recovery to the flat state. The current–bending radius plot shows that the device maintains a remarkably stable current output of ~ 0.02 A across all tested bending radii, even at the extreme radius of 2 mm. The LED remained continuously lit under all bending conditions, visually verifying uninterrupted circuit connectivity. Notably, the current returned to its initial value after the sample was flattened, indicating fully reversible electrical performance with no permanent damage to the conductive network. This outstanding mechanical-electrical stability is attributed to the excellent flexibility of the 10 wt% PVA-based ink film, which accommodates large deformations without cracking or delaminating from the PI substrate. These findings confirm the device’s suitability for wearable applications, where repeated bending and deformation are inevitable. 4. Conclusion In this work, we systematically investigated the regulatory effect of PVA concentration on the properties of PEDOT:PSS/Cu@Ag composite conductive inks and the performance of flexible Joule heating devices. The ink viscosity exhibited a strong concentration dependence (454.09 mPa·s, 884.14 mPa·s, 2917.01 mPa·s for 5 wt%, 10 wt%, 15 wt% PVA), directly governing printability, film formation, and subsequent device performance. The 10 wt% PVA-based device achieved optimal electrothermal efficiency, reaching 100°C at ~ 3 V, due to the balanced film-forming ability and electrical conductivity of the ink. By engineering electrode configurations, we further tuned the device performance: the shunt-connected design achieved a maximum temperature of 110.7°C at 3 V, outperforming single-line and series-connected counterparts by virtue of its reduced total resistance and enhanced current density. Mechanical bending tests confirmed that the optimized shunt-connected device maintained stable current output and circuit continuity even at an extreme bending radius of 2 mm under 3 V driving, with fully reversible performance after recovery to the flat state. This study clarifies the structure–property relationship of PVA-regulated conductive inks and establishes electrode configuration engineering as a viable strategy for performance tuning. The proposed 10 wt% PVA-based conductive ink and shunt-connected device design provide a practical solution for developing high-efficiency, low-voltage-driven, and mechanically robust flexible Joule heating devices, with great potential for wearable thermotherapy, portable thermal management, and other flexible electronic applications. Declarations Conflict of Interest The authors declare that they have no conflicts of interest. Author Contribution R.Y. (Rongrong Yuan): Conceptualization, methodology, supervision, funding acquisition, writing—review & editing.Y.S. (Yizhe Sun): Investigation, data curation, formal analysis, writing—original draft.X.D. (Xiuzhi Du): Experiment execution (conductive ink preparation and viscosity measurement), data collection.L.T. (Lu Tao): Experiment execution (device fabrication and electrothermal performance testing), validation.X.C. (Xinhui Cui): Experiment execution (mechanical robustness and adhesion tests), data analysis.Z.L. (Zhipeng Li): Visualization, preparation of figures 1–4, supplementary materials.X.Z. (Xinqun Zhang): Resources, project administration, review & editing of the manuscript.All authors have read and approved the final version of the manuscript, and agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. Acknowledgements The authors thank the financial support by Educational Commission Key (Key grant) Project of Anhui Province of China (Nos. 2024AH040204 and 2025AHGXZK30220 ) and Research Funds of Chuzhou Polytechnic (Nos. QDJ-2024-2, QDJ-2025-1, QDJ-2025-3 and xjgz2024002, CZZY-HX-2024-40, 2025ctzygz01, ZKY-2024-4 and Nos.2025aikc14). Conflict of Interest The authors declare that they have no conflicts of interest. Data Availability All data generated or analysed during this study are included in this published article and its supplementary information files. 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Li, Moisture-electric generators working in subzero environments based on laser-engraved hygroscopic hydrogel arrays. ACS Nano. 19 , 3807–3817 (2025) G. Li, K. Huang, J. Deng, M. Guo, M. Cai, Y. Zhang, C.F. Guo, Highly conducting and stretchable double-network hydrogel for soft bioelectronics. Adv. Mater. 34 , e2200261 (2022) Additional Declarations No competing interests reported. Supplementary Files SupportingInformation.docx Appendix A. Supplementary data Supporting Information is available from the Online Library or from the author. Cite Share Download PDF Status: Posted Version 1 posted 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. 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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-9105142","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":609244482,"identity":"99d48c97-e4fd-4062-8adf-b7c399c7e3b7","order_by":0,"name":"Rongrong Yuan","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA9ElEQVRIiWNgGAWjYNCDBAMJOTb25gMkaPlQYWHMx3MsgXgdjDPOVCTOk8hRwKvK4Ebys8cVFXfstrf3Hn7N2yaR3saQw8Dwo2IbHi1p5oZnzjxLnnPmXJo1UEtuG8PZA4w9Z27j0ZJgJtnYdjhZQiLHzBishbEvgZmxDZ+W9G8oWtLZmHkMCGjJAdtiB9Ri/HDGGYkENjYCWiTPvCmTbDhzOEGC54wZMJAlDNt42BIO4vML3/H0bZINFYftJdh7jD8kGNTJy89/fPDBjwrcWhQOQOjEBgYGNgmY6AGc6oFAvgFC2wMx8wd8KkfBKBgFo2DkAgDU+VlSq3JCDQAAAABJRU5ErkJggg==","orcid":"","institution":"Chuzhou Polytechnic","correspondingAuthor":true,"prefix":"","firstName":"Rongrong","middleName":"","lastName":"Yuan","suffix":""},{"id":609244483,"identity":"0af0b339-f646-4cc6-8eb7-6ca4f4563258","order_by":1,"name":"Yizhe Sun","email":"","orcid":"","institution":"Chuzhou Polytechnic","correspondingAuthor":false,"prefix":"","firstName":"Yizhe","middleName":"","lastName":"Sun","suffix":""},{"id":609244485,"identity":"46e8fafc-2b80-41fb-bea0-63a42931b33c","order_by":2,"name":"Xiuzhi Du","email":"","orcid":"","institution":"Chuzhou Polytechnic","correspondingAuthor":false,"prefix":"","firstName":"Xiuzhi","middleName":"","lastName":"Du","suffix":""},{"id":609244487,"identity":"d544adda-8dee-4205-beb8-f01baacc3fc2","order_by":3,"name":"Lu Tao","email":"","orcid":"","institution":"Chuzhou Polytechnic","correspondingAuthor":false,"prefix":"","firstName":"Lu","middleName":"","lastName":"Tao","suffix":""},{"id":609244488,"identity":"e385588b-6b70-44dd-8202-f512a5725608","order_by":4,"name":"Xinhui Cui","email":"","orcid":"","institution":"Chuzhou Polytechnic","correspondingAuthor":false,"prefix":"","firstName":"Xinhui","middleName":"","lastName":"Cui","suffix":""},{"id":609244490,"identity":"b64580a2-4f56-4418-aa9f-77f114b03082","order_by":5,"name":"Zhipeng Li","email":"","orcid":"","institution":"Chuzhou Polytechnic","correspondingAuthor":false,"prefix":"","firstName":"Zhipeng","middleName":"","lastName":"Li","suffix":""},{"id":609244492,"identity":"41387bd4-4a00-445e-84ee-3f7c3b37878c","order_by":6,"name":"Xinqun Zhang","email":"","orcid":"","institution":"Chuzhou Polytechnic","correspondingAuthor":false,"prefix":"","firstName":"Xinqun","middleName":"","lastName":"Zhang","suffix":""}],"badges":[],"createdAt":"2026-03-12 13:08:29","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9105142/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9105142/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":105530346,"identity":"c1007f83-0896-4430-a86e-ff4885af5784","added_by":"auto","created_at":"2026-03-27 05:41:42","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":590600,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic illustration of the fabrication process of flexible Joule heating devices based on PVA-regulated conductive inks and their electrothermal performance characterization. (a) Schematic fabrication flow: (i) Dissolution of PVA powders with different mass fractions (5%, 10%, 15%) to form aqueous PVA solutions; (ii) Homogeneous mixing of PVA solution with PEDOT:PSS, Cu@Ag nanoparticles (10%), glycerin, BHT, CNF, SDS, and SA to prepare composite conductive inks; (iii) Doctor-blade printing of the inks on PI substrates assisted by a mask, followed by thermal curing; (iv) Cutting the cured ink patterns into designed shapes; (v) Bonding and packaging of the devices using Ag paste, Cu wires, and PI tape. (b) Photograph of the electrothermal performance test platform, consisting of a variable voltage source, the as-fabricated sample, a temperature sensor, and a laptop for data recording. (c) Infrared thermal images of the flexible heating devices under 3 V and 5 V driving voltages, showing the temperature distribution and maximum temperatures of 104.2 °C and 134 °C, respectively.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-9105142/v1/edf9cec35294548a68fbec06.png"},{"id":105530343,"identity":"ef06d438-72d6-46e5-aeeb-a15cffe95a79","added_by":"auto","created_at":"2026-03-27 05:41:41","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":455393,"visible":true,"origin":"","legend":"\u003cp\u003eElectrothermal and electrical performance of flexible heating devices based on conductive inks with different PVA concentrations. (a) Infrared thermal images of devices No.1 (5 wt% PVA), No.2 (10 wt% PVA), and No.3 (15 wt% PVA) at their initial temperatures and the maximum temperatures under specific driving voltages, respectively. (b) Voltage-dependent temperature curves of the three devices, illustrating the voltage thresholds required to reach the target temperature of 100 °C. (c) Variation of electrical resistance of the three devices with increasing driving voltage, reflecting the conductive behavior regulation by PVA concentration.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-9105142/v1/24ed184fb3faf6e2c63e71a2.png"},{"id":105530320,"identity":"6977a337-fc76-4101-bbbe-2e7d2944ab5e","added_by":"auto","created_at":"2026-03-27 05:41:28","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":287062,"visible":true,"origin":"","legend":"\u003cp\u003eTunable electrothermal and electrical performance of 10 wt% PVA-based flexible heating devices under different electrode configurations. (a) Schematic diagrams of the three electrode designs: (i) single-line, (ii) series-connected (1+2+3), and (iii) shunt-connected (1//2//3). (b) Voltage-dependent temperature curve of the single-line configuration, with a maximum temperature of 104.2 °C at 3 V. (c) Voltage-dependent temperature curve of the series-connected configuration, reaching a maximum of 105.5 °C at 7.5 V. (d) Voltage-dependent temperature curve of the shunt-connected configuration, achieving the highest peak temperature of 110.7 °C at 3 V. (e–g) Corresponding resistance-voltage characteristics of the single-line (e), series-connected (f), and shunt-connected (g) configurations, respectively.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-9105142/v1/6423ec078f70e19d4866eb17.png"},{"id":105530322,"identity":"641978ea-5404-4aad-b503-6947035cb171","added_by":"auto","created_at":"2026-03-27 05:41:29","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":296204,"visible":true,"origin":"","legend":"\u003cp\u003eElectrical stability and mechanical robustness of the shunt-connected flexible heating device under different bending radii, driven at a constant 3 V. The plot shows the current output as a function of bending radius (20 mm, 10 mm, 5 mm, 2 mm) and recovery to the flat state. The insets are photographs of the device under corresponding bending conditions, with a series-connected LED confirming continuous circuit connectivity.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-9105142/v1/bf030a087faf7979cf07f420.png"},{"id":105975686,"identity":"61e49d15-cb62-49f8-9864-7ec17c56744a","added_by":"auto","created_at":"2026-04-02 05:11:18","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2741466,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9105142/v1/af480077-a148-4fe0-9eb3-dc482d1ab49e.pdf"},{"id":105530358,"identity":"edefc032-34b3-46c1-ae22-e61d86b3f43a","added_by":"auto","created_at":"2026-03-27 05:41:47","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1055432,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eAppendix A. Supplementary data\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSupporting Information is available from the Online Library or from the author.\u003c/p\u003e","description":"","filename":"SupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-9105142/v1/d8b2b5433aa1155a2f2c6c9a.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"PVA-Concentration-Regulated Conductive Inks for Low-Voltage-Driven Flexible Joule Heating Devices with Tunable Performance and Mechanical Robustness","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eFlexible Joule heating devices have attracted significant attention for applications in wearable thermotherapy\u003csup\u003e[\u003cspan additionalcitationids=\"CR2 CR3 CR4\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/sup\u003eand flexible electronics\u003csup\u003e[\u003cspan additionalcitationids=\"CR7 CR8 CR9\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e, due to their lightweight, conformable nature, and efficient electrothermal conversion. Conductive inks, as the core material of these devices, must simultaneously satisfy requirements of high electrical conductivity, excellent mechanical flexibility, good printability, and low-voltage operation\u003csup\u003e[\u003cspan additionalcitationids=\"CR12 CR13 CR14 CR15\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e. Polyvinyl alcohol (PVA) is a widely used polymer matrix for conductive inks due to its water solubility, biocompatibility, and good film-forming ability\u003csup\u003e[\u003cspan additionalcitationids=\"CR18 CR19\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e. However, the concentration of PVA in the ink formulation plays a critical role in determining the final properties of the composite: low PVA concentrations may lead to poor film integrity and mechanical stability, while excessive PVA can form a thick insulating layer that hinders electron transport and reduces conductivity. Despite the importance of PVA concentration, a systematic study on its effect on the electrothermal performance of flexible heating devices is still lacking. Moreover, the scalability and performance tunability of these devices through electrode configuration (single-line, series, parallel) remain underexplored, and their mechanical robustness under extreme bending conditions is critical for practical applications.\u003c/p\u003e \u003cp\u003eIn this work, we address these gaps by systematically investigating the effect of PVA concentrations (5 wt%, 10 wt%, 15 wt%) on the properties of PEDOT:PSS/ Cu@Ag composite conductive inks. We fabricate flexible heating devices and evaluate their electrothermal performance, then explore electrode configuration as a strategy to tune performance. Finally, we assess the mechanical robustness of the optimized device under extreme bending conditions. Our results provide a clear understanding of the role of PVA concentration and electrode design in governing the performance of flexible Joule heating devices, offering a promising strategy for the design of high-performance flexible heating materials.\u003c/p\u003e"},{"header":"2. Experimental Section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n\u003ch2\u003e2.1 Materials\u003c/h2\u003e\n\u003cp\u003ePoly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), polyvinyl alcohol (PVA, molecular weight\u0026thinsp;~\u0026thinsp;89,000\u0026ndash;98,000), Cu@Ag core\u0026ndash;shell nanoparticles (10 wt% Ag content, average particle size 2\u0026ndash;5 \u0026micro;m), glycerin (purity\u0026thinsp;\u0026ge;\u0026thinsp;99.5%), butylated hydroxytoluene (BHT), cellulose nanofibers (CNF), sodium dodecyl sulfate (SDS), and sodium alginate (SA) were used as received. The experimental substrate was ultra-thin polyimide (PI) film (thickness 0.025 mm).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n\u003ch2\u003e2.2 Formulation Preparation\u003c/h2\u003e\n\u003cp\u003eThree conductive ink formulations were prepared with PVA concentrations of 5 wt%, 10 wt%, and 15 wt% as the polymer matrix. The detailed mass ratios of all components (PVA, PEDOT:PSS, Cu@Ag nanoparticles, glycerin, BHT, CNF, SDS, and SA) are listed in Table SI.\u003c/p\u003e\n\u003cp\u003eEach ink was prepared via a two-step process:\u003c/p\u003e\n\u003col\u003e\n\u003cli\u003e\n\u003cp\u003ePVA powder was dissolved in deionized water at 90\u0026deg;C under magnetic stirring (300 rpm) for 1 h to form a homogeneous aqueous solution.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003eThe PVA solution was cooled to room temperature, and PEDOT:PSS, Cu@Ag nanoparticles, glycerin, BHT, CNF, SDS, and SA were added sequentially. The mixture was stirred at 300 rpm for 3 min, followed by ultrasonic dispersion (40 kHz, 300 W) for 5 min to break up agglomerates and ensure uniform dispersion of the conductive fillers.\u003c/p\u003e\n\u003c/li\u003e\n\u003c/ol\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n\u003ch2\u003e2.3 Printing and Drying\u003c/h2\u003e\n\u003cp\u003eA stainless steel mask with custom patterns (line width: 2 mm, length: 20 mm, spacing: 5 mm) was clamped onto the PI substrate. The ink was coated using a stainless steel doctor blade (45\u0026deg;, 50 mm/s, controlled pressure: 10 N). After printing, the samples were dried in a convection oven with air circulation at 90\u0026deg;C for 15 min. The film thickness was controlled by the mask aperture (500 \u0026micro;m). For scalability tests, three electrode configurations (single-line, series, and shunt) were fabricated by adjusting the mask pattern.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n\u003ch2\u003e2.4 Performance Characterization\u003c/h2\u003e\n\u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\n\u003ch2\u003e2.4.1 Viscosity Measurement\u003c/h2\u003e\nThe viscosity of PVA solutions with different concentrations was measured using a rotational viscometer, with digital photographs of the measurement process shown in Supplementary Figure S2.\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\n\u003ch2\u003e2.4.2 Electrothermal and Electrical Performance\u003c/h2\u003e\nThe electrothermal performance was characterized using a customized test platform consisting of a variable voltage source (0\u0026ndash;30 V), a temperature sensor, and a laptop for data recording. Voltage-dependent temperature curves and maximum temperatures were obtained via infrared thermal imaging.\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\n\u003ch2\u003e2.4.3 Mechanical Robustness Test\u003c/h2\u003e\nThe shunt-connected device was subjected to bending tests with radii of 20 mm, 10 mm, 5 mm, and 2 mm under a constant 3 V driving voltage. The device was connected in series with a green LED bead to visually confirm circuit continuity, and the current output was recorded under each bending condition.\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\n\u003ch2\u003e2.4.4 Adhesion Test\u003c/h2\u003e\nThe adhesion of the ink film to the PI substrate was evaluated via a cross-hatch test following ASTM D3359. A multi-blade cutter was used to create a grid pattern, followed by application and removal of 3M tape (model 600-1PK). Adhesion grade was determined based on the ink shedding area, as specified in Table SII.\u003c/div\u003e\n\u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n\u003ch2\u003e3.1 Fabrication and Characterization of Flexible Heating Devices\u003c/h2\u003e\nThe fabrication process of flexible Joule heating devices based on PVA-regulated conductive inks is illustrated in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. The two-step preparation method ensures uniform dispersion of conductive fillers in the PVA matrix: PVA powders of different concentrations are first dissolved to form aqueous solutions (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ea(i)), then mixed with PEDOT:PSS, Cu@Ag nanoparticles, and functional additives (glycerin, BHT, CNF, SDS, SA) to prepare composite conductive inks (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ea(ii)). The ink is then printed on PI substrates via mask-assisted doctor-blade coating, followed by thermal curing, cutting into designed wavy/linear patterns, and packaging with Ag paste, Cu wires, and PI tape to complete device assembly (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ea(iii\u0026ndash;v)).\n\u003cp\u003eA customized electrothermal test platform (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ec) was built to characterize device performance, and infrared thermal imaging (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eb) confirmed the devices\u0026rsquo; ability to generate uniform Joule heat, with maximum temperatures of 134\u0026deg;C and 104.2\u0026deg;C under 5 V and 3 V driving, respectively. The viscosity of the PVA solutions exhibited a significant concentration dependence: 454.09 mPa\u0026middot;s (5 wt% PVA), 884.14 mPa\u0026middot;s (10 wt% PVA), and 2917.01 mPa\u0026middot;s (15 wt% PVA) (Supplementary Figure S2). This viscosity variation directly impacts ink printability and film formation\u0026mdash;low viscosity (5 wt% PVA) leads to poor film integrity, while excessively high viscosity (15 wt% PVA) hinders ink spreading and filler dispersion, laying the foundation for the divergent electrothermal performance of the three devices.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n\u003ch2\u003e3.2 Effect of PVA Concentration on Electrothermal Performance\u003c/h2\u003e\n\u003cp\u003eThe electrothermal conversion efficiency and electrical stability of devices with different PVA concentrations (No.1: 5 wt%, No.2: 10 wt%, No.3: 15 wt%) were systematically evaluated (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). Infrared thermal images (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea) show distinct temperature distributions for each device at initial temperatures and under optimal driving voltages: No.2 (10 wt% PVA) reaches 104.2\u0026deg;C at 3 V, No.1 (5 wt% PVA) reaches 111.8\u0026deg;C at 5.5 V, and No.3 (15 wt% PVA) only reaches 98.3\u0026deg;C even at 8 V.\u003c/p\u003e\n\u003cp\u003eVoltage-dependent temperature curves (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb) further quantify these differences: the No.2 device achieves the target temperature of 100\u0026deg;C at ~\u0026thinsp;3 V, demonstrating the highest electrothermal conversion efficiency. In contrast, the No.1 device requires\u0026thinsp;~\u0026thinsp;5.5 V to reach 100\u0026deg;C, and the No.3 device fails to attain this threshold even at the maximum tested voltage of 8 V. The underlying mechanism is revealed by the resistance\u0026ndash;voltage characteristics (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec): the No.2 device maintains the lowest and most stable resistance across the entire voltage range, facilitating high current density and efficient Joule heat generation (Q\u0026thinsp;=\u0026thinsp;I\u0026sup2;Rt). The No.1 device exhibits a gradual increase in resistance with voltage, likely due to poor film-forming ability of the low-concentration PVA matrix, which causes degradation of the conductive network under thermal stress. The No.3 device shows an extremely high initial resistance that decreases with increasing voltage, attributed to the excessive PVA forming a thick insulating layer that impedes electron transport; the resistance reduction at high voltages is likely due to thermal activation of charge carriers in the conductive fillers. These results confirm that 10 wt% PVA strikes an optimal balance between film-forming ability and electrical conductivity.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n\u003ch2\u003e3.3 Tuning Electrothermal Performance via Electrode Configuration\u003c/h2\u003e\n\u003cp\u003eTo further optimize the performance of the 10 wt% PVA-based ink, three electrode configurations (single-line, series-connected, shunt-connected) were fabricated and characterized (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). Schematic diagrams of the three designs are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea(i\u0026ndash;iii): single-line, series-connected (1\u0026thinsp;+\u0026thinsp;2+3), and shunt-connected (1//2//3).\u003c/p\u003e\n\u003cp\u003eThe voltage-dependent electrothermal behavior of each configuration is presented in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb\u0026ndash;d. The single-line device (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb) achieves a maximum temperature of 104.2\u0026deg;C at 3 V, with a symmetric temperature rise and fall with voltage variation, indicating stable low-voltage heating. The series-connected device (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ec) requires a much higher voltage of 7.5 V to reach a comparable maximum temperature of 105.5\u0026deg;C, due to its increased total resistance limiting current density. The shunt-connected device (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ed) outperforms the other two designs, attaining a maximum temperature of 110.7\u0026deg;C at 3 V, with a steeper temperature rise rate and superior electrothermal efficiency.\u003c/p\u003e\n\u003cp\u003eCorresponding resistance characteristics (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ee\u0026ndash;g) elucidate the structural origin of these performance differences. The single-line device (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ee) maintains a stable resistance of ~\u0026thinsp;7\u0026ndash;8 Ω across all sampling points, ensuring consistent current density. The series-connected device (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ef) exhibits a significantly higher baseline resistance of ~\u0026thinsp;16 Ω, directly explaining the need for elevated driving voltage. The shunt-connected device (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eg) has a drastically reduced initial resistance of ~\u0026thinsp;2 Ω, enabling a much higher current density under 3 V and thus enhanced Joule heating efficiency. These results demonstrate that electrode configuration is a facile and effective strategy to tune the electrothermal performance of flexible heating devices, with the shunt-connected design being optimal for low-voltage, high-temperature applications.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\n\u003ch2\u003e3.4 Mechanical Robustness under Extreme Bending\u003c/h2\u003e\n\u003cp\u003eThe mechanical robustness and electrical stability of the optimized shunt-connected device were evaluated via bending tests under a constant 3 V driving voltage (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). The device was connected in series with an LED bead to visually confirm circuit continuity, with tests conducted at bending radii of 20 mm, 10 mm, 5 mm, 2 mm, and recovery to the flat state.\u003c/p\u003e\n\u003cp\u003eThe current\u0026ndash;bending radius plot shows that the device maintains a remarkably stable current output of ~\u0026thinsp;0.02 A across all tested bending radii, even at the extreme radius of 2 mm. The LED remained continuously lit under all bending conditions, visually verifying uninterrupted circuit connectivity. Notably, the current returned to its initial value after the sample was flattened, indicating fully reversible electrical performance with no permanent damage to the conductive network. This outstanding mechanical-electrical stability is attributed to the excellent flexibility of the 10 wt% PVA-based ink film, which accommodates large deformations without cracking or delaminating from the PI substrate. These findings confirm the device\u0026rsquo;s suitability for wearable applications, where repeated bending and deformation are inevitable.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn this work, we systematically investigated the regulatory effect of PVA concentration on the properties of PEDOT:PSS/Cu@Ag composite conductive inks and the performance of flexible Joule heating devices. The ink viscosity exhibited a strong concentration dependence (454.09 mPa\u0026middot;s, 884.14 mPa\u0026middot;s, 2917.01 mPa\u0026middot;s for 5 wt%, 10 wt%, 15 wt% PVA), directly governing printability, film formation, and subsequent device performance. The 10 wt% PVA-based device achieved optimal electrothermal efficiency, reaching 100\u0026deg;C at ~\u0026thinsp;3 V, due to the balanced film-forming ability and electrical conductivity of the ink.\u003c/p\u003e \u003cp\u003eBy engineering electrode configurations, we further tuned the device performance: the shunt-connected design achieved a maximum temperature of 110.7\u0026deg;C at 3 V, outperforming single-line and series-connected counterparts by virtue of its reduced total resistance and enhanced current density. Mechanical bending tests confirmed that the optimized shunt-connected device maintained stable current output and circuit continuity even at an extreme bending radius of 2 mm under 3 V driving, with fully reversible performance after recovery to the flat state.\u003c/p\u003e \u003cp\u003eThis study clarifies the structure\u0026ndash;property relationship of PVA-regulated conductive inks and establishes electrode configuration engineering as a viable strategy for performance tuning. The proposed 10 wt% PVA-based conductive ink and shunt-connected device design provide a practical solution for developing high-efficiency, low-voltage-driven, and mechanically robust flexible Joule heating devices, with great potential for wearable thermotherapy, portable thermal management, and other flexible electronic applications.\u003c/p\u003e"},{"header":"Declarations","content":"\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no conflicts of interest.\u003c/p\u003e\n\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\n\u003cp\u003eR.Y. (Rongrong Yuan): Conceptualization, methodology, supervision, funding acquisition, writing\u0026mdash;review \u0026amp; editing.Y.S. (Yizhe Sun): Investigation, data curation, formal analysis, writing\u0026mdash;original draft.X.D. (Xiuzhi Du): Experiment execution (conductive ink preparation and viscosity measurement), data collection.L.T. (Lu Tao): Experiment execution (device fabrication and electrothermal performance testing), validation.X.C. (Xinhui Cui): Experiment execution (mechanical robustness and adhesion tests), data analysis.Z.L. (Zhipeng Li): Visualization, preparation of figures 1\u0026ndash;4, supplementary materials.X.Z. (Xinqun Zhang): Resources, project administration, review \u0026amp; editing of the manuscript.All authors have read and approved the final version of the manuscript, and agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.\u003c/p\u003e\n\u003ch2\u003eAcknowledgements\u003c/h2\u003e\n\u003cp\u003eThe authors thank the financial support by Educational Commission Key (Key grant) Project of Anhui Province of China (Nos. 2024AH040204 and 2025AHGXZK30220 ) and Research Funds of Chuzhou Polytechnic (Nos. QDJ-2024-2, QDJ-2025-1, QDJ-2025-3 and xjgz2024002, CZZY-HX-2024-40, 2025ctzygz01, ZKY-2024-4 and Nos.2025aikc14).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no conflicts of interest.\u003c/p\u003e\n\u003ch2\u003eData Availability\u003c/h2\u003e\n\u003cp\u003eAll data generated or analysed during this study are included in this published article and its supplementary information files.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eZ. Liu, X. Wang, Y. He, Y. Yang, Z. Wang, J. Shi, G. Liu, F. Kong, B. Zhu, R. Xiong, Stretchable multifunctional wearable system for real-time and on-demand thermotherapy of arthritis. Microsyst. Nanoeng. \u003cb\u003e11\u003c/b\u003e, 84 (2025)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJ. Liu, L. Zhang, H. Zhao, Z. 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Mater. \u003cb\u003e34\u003c/b\u003e, e2200261 (2022)\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Conductive slurry, Flexible devices, Joule heating, Polyvinyl Alcohol (PVA)","lastPublishedDoi":"10.21203/rs.3.rs-9105142/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9105142/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePolyvinyl alcohol (PVA) concentration plays a key role in the printability, electrical conductivity, and electrothermal performance of conductive inks for flexible Joule heating devices. In this work, PEDOT:PSS/Cu@Ag composite inks with 5 wt%, 10 wt%, and 15 wt% PVA were prepared and systematically investigated. The viscosities of the three solutions were 454.09, 884.14, and 2917.01 mPa\u0026middot;s, respectively. Flexible devices were fabricated on polyimide substrates via doctor-blade printing and thermal curing. The 10 wt% PVA-based device exhibited the optimal performance, reaching 100\u0026deg;C at approximately 3 V. By designing single-line, series, and shunt electrode configurations, the shunt-connected device achieved the highest heating temperature of 110.7\u0026deg;C at 3 V. Bending tests demonstrated that the device maintained stable circuit continuity under a bending radius down to 2 mm at 3 V driving. This study provides an effective strategy for designing low-voltage-driven, mechanically robust flexible heating devices for wearable electronic applications.\u003c/p\u003e","manuscriptTitle":"PVA-Concentration-Regulated Conductive Inks for Low-Voltage-Driven Flexible Joule Heating Devices with Tunable Performance and Mechanical Robustness","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-27 05:39:46","doi":"10.21203/rs.3.rs-9105142/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"39863bfa-d542-462a-89e7-01be00eb6412","owner":[],"postedDate":"March 27th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-02T05:10:46+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-27 05:39:46","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9105142","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9105142","identity":"rs-9105142","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}