Microstructure-oriented high-sensitivity pressure sensor: a cross-linked ionic poly(urea-urethane) with mechanical robustness, elasticity, and ionic liquid affinitation

Abstract

The primary challenge in developing highly sensitive skin-inspired polymeric sensors with superior strength, toughness, and exceptional self-healing capabilities is the inherent brittleness of the polymer matrix, with the difficulty in constructing efficient charge transport pathways. This study proposed a new type of cross-linked ionic poly(urea-urethane) (PUU) synthesized by strategically incorporating ionic bonds into PUU matrix combining the dynamic cross-linking mechanisms of hindered urea bonds and hydrogen bonds. These materials use electrostatic interactions between the polymer network and ILs to form stable ion transport channels, effectively addressing the liquid leakage issue inherent in conventional ionogels. The synthesized PUU material exhibited outstanding mechanical properties, featuring tensile strength of 13.0 MPa and elongation at break of about 1270 %. More importantly, the PUU network displayed excellent ionic liquid affinity (contact angle of 48.5°) and high self-healing efficiency (80.8 % at 60 °C). Furthermore, flexible sensors constructed by incorporating ionic liquids (ILs) into PUU with special microstructures presented high sensitivity (−6.5 kPa⁻¹), rapid response time (48 ms), and moderate detection range (0.08–4 kPa), enabling precise monitoring of human activities. These multifunctional cross-linked PUU elastomers demonstrate significant potential for applications in robust self-healing materials as well as in resistive pressure sensors.