A high-strength Janus-structured aramid nanofiber/calcium sulfate crystal–silver nanowire composite film for integrated insulation, sensing, and Joule heating

Abstract

Developing flexible electronic materials that integrate high strength, electrical insulation, and reliable sensing remains challenging. This is because the void structures inherent in nanocomposite films significantly compromise their mechanical performance and functionality. This study systematically investigates the influence of calcium sulfate crystallite (CSC) dimensions and content on the void structure, mechanical properties, and functional characteristics of aramid nanofiber (ANF) composite films via the incorporation of CSCs into the ANF matrix. The underlying mechanisms governing these effects were thoroughly examined. CSCs with different dimensions were first synthesized via a hydrothermal method. Then, ANF/CSC composite films were fabricated through a sequential process of vacuum-assisted filtration followed by hot-pressing. The results indicate that the composite film incorporating medium-sized CSCs at 30 wt% exhibits the optimal reinforcement effect, achieving a tensile strength of 177.7 MPa, which represents a 289% improvement compared to the pristine ANF film. It was found that the CSCs form a three-dimensional network architecture within the ANF matrix, which effectively fills the voids and enhances the degree of orientation. Furthermore, a Janus-structured ANF/CSC–ANF/AgNW film was constructed, achieving the integration of electrical insulation on one side and conductivity on the other. The sample containing 30 wt% AgNWs exhibited rapid Joule heating, reaching 110 °C within 10 seconds under an applied voltage of 10 V. Moreover, it maintained stable electrical performance even after 750 bending cycles in sensing tests. This study provides a strategy to effectively enhance the mechanical and insulating properties of composite materials through a three-dimensional network of CSCs and ANFs and achieves integrated assembly of an insulating substrate and a conductive sensing layer by introducing a Janus structure. It offers greater possibilities for the application of high-performance flexible electronic devices in extreme environments.