Y. Lu, J-W Jeon, E.K. Wujcik
The University of Alabama,
Keywords: strain sensor, polymer, homogeneous, linear, repeatable, autonomous, self-healing
Summary:Wearable strain sensors are essential for the realization of applications in the broad fields of remote healthcare monitoring, soft robots, immersive gaming, among many others. These flexible sensors should be comfortably adhered to skin and capable of monitoring human motions with high accuracy, as well as exhibiting excellent durability. However, it is challenging to develop electronic materials that possess the properties of skin—compliant, elastic, stretchable, and self-healable. This work demonstrates a new regenerative polymer complex as a skin-like electronic material. It exhibits ultrahigh stretchability (1935%), excellent repeatable autonomous self-healing ability (repeating healing efficiency > 98%), and exceptional linearity (R2 > 0.995) — outperforming current reported wearable strain sensors. The partially deprotonated polymer electrolyte, protonic acid and doped conductive polymer, under ambient conditions, synergistically construct a regenerative dynamic network of polymer complex crosslinked by hydrogen bonds and electrostatic interactions, which enables ultrahigh stretchability and repeatable self-healing. Sensitive strain-responsive geometric and piezoresistive mechanisms of the material owing to the homogenous and viscoelastic nature provide excellent linear responses to omnidirectional tensile strain and bending deformations. Furthermore, this material is scalable and simple to process in an environmentally-friendly manner, paving the way for the next generation flexible electronics. Though many stretchable electronic materials are developed as wearable strain sensors and electronic skins, their performance still struggles in terms of stretchability, self-healing ability, and accuracy. Conductive nanofiller based stretchable materials require a delicately designed structure or percolation network to achieve a conductive path under large strains. This makes the sensors suffer low linearity, limited stretchability, and poor long-term durability. Here, we introduce a new polymer complex strategy to fabricate an ultra-stretchable, and autonomously self-healable electronic material. The polymer complex system is composed of a polymer electrolyte, intrinsic conductive polymer, and protonic acid cross-linker. The homogenous and isotropic nature ensures the sensor to sense strain omni-directionally with an excellent linearity, which is unseen in piezoresistive strain sensors. Moreover, due to the regenerative dynamic network crosslinked via hydrogen bonds and electrostatic interactions in the polymer complex, the material displays an unprecedented stretchability and repeatable autonomous self-healing ability. The overall performance of self-healing and strain sensing are superior, benefiting from the inherent properties of the system. We believe the concept of the present polymer complex system is applicable to the entire class of related polymer complexes, giving insights and advancing polymer-based stretchable electronic materials.