Highly sensitive transparent piezoionic materials and their applicability as printable pressure sensors

Abstract

Hybrid materials based on ionic liquids (ILs) and polymers represent an emerging an interesting approach for an increasing number of applications, including sensors and actuators. This work reports on the development of transparent piezoionic materials based on a thermoplastic elastomer styrene-ethylene-butylene-styrene (SEBS) containing 20 wt% of the IL 1-butyl-3-methylimidazolium dicyanamide ([Bmim][N(CN)2]), suitable for pressure sensing applications. The incorporation of [Bmim][N(CN)2] within the SEBS polymer matrix induces the presence of small voids within the polymer matrix and the most significant physical-chemical changes are the increase of the electrical conductivity (1.44 × 10−14 S cm−1 to 2.94 × 10−11 ±4.2 × 10−4 S cm−1) from the pristine polymer to the hybrid material and the improved piezoresistive response, as a result of the variation of the ionic conductivity under mechanical solicitation. This piezoionic response was evaluated under loading and unloading compressive cycles with applied forces up to 5 N and 10 N. Independently of the applied force, the electrical resistance decreases with increasing pressure and shows a pressure sensitivity of approximately 25 kΩ N−1 in a dynamic range from 0 to 10 N. The suitability of the developed hybrid material as transparent pressure sensor was evaluated through the development of a touch pad prototype compatible with printing technologies.