Fabrication of flexible polymer composites with tailored anisotropic electrical conductivity via ultrasound-assisted vat photopolymerization

Flexible conductive polymer composites (FCPCs) are critical to advancing flexible electronics because they combine mechanical flexibility and electrical conductivity. Conventional fabrication approaches rely on incorporating a high weight fraction of randomly dispersed conductive filler throughout the polymer to achieve long-range conductivity, which decreases flexibility of the material. Here, we present a method to achieve long-range electrical conductivity in FCPCs without sacrificing flexibility, using ultrasound-assisted vat photopolymerization (VP). Ultrasound wave fields spatially organize a low weight fraction of conductive filler into a percolated, long-range network within a flexible photopolymer matrix. We investigate the influence of fabrication parameters on electrical conductivity under both quasi-static and dynamic loading conditions. Our results show that increasing both the filler fraction and the ultrasound amplitude increases conductivity, achieving a maximum value of 1936 S/m, which surpasses that produced by other methods. Importantly, the resulting FCPCs maintain flexibility, enduring twice the bending strain of composites with a high fraction of randomly distributed filler. To demonstrate the method’s scalability, we fabricate an 18-mm-long strain sensor, which is nearly twice the length achieved by others, and create multilayer FCPCs with complex geometries. These results highlight the promise of ultrasound-assisted VP as a scalable platform for fabricating next-generation flexible electronic devices.