Chitosan-based film composites as tunable strain sensors

Abstract

Polymer composite strain gauges represent a significant area of interest due to the potential for high mechanical strain measurements. Their physical-mechanical properties and usability render them indispensable in wearable and biocompatible flexible electronics. Herein, we present the experimental findings regarding the composites based on chitosan matrix with few-layered graphene (FLG), which is uniformly distributed in the matrix through the use of amphiphilic stabilizers Pluronic F108 and polyvinylpyrrolidone. The variation of the stabilizers and FLG content enables the modification of composite morphology and subsequent alteration of piezoresistive effect. The resistivity of the composites ranges from 1.6 up to 130 000 Ohm·cm, corresponding to a change in the strain gauge factor from 1.3 to 5.7. To elucidate the morphology and physical nature of the piezoresistive effect, the mechanisms of electrical conductivity were analyzed from room temperature down to cryogenic ones. At sufficiently high FLG content, FLG nanoparticles are observed to be in contact with each other in the current pathways; in the composites with lower FLG content, there are polymer gaps between the FLG particles. At low temperatures, the electrical conduction mechanism is variable-range hopping, which is caused by the defectiveness and small dimensions of the FLG particles. The composites have been demonstrated to exhibit functionality at a strain value of up to 40 %, with a Young’s modulus of 270 MPa and a tensile strength of 68 MPa. Coupled with their biocompatibility, the composites are a promising candidate for biomechanics applications.