Morphology-Driven Electromechanical Performance of Graphene-Based Electrofluids for Emerging Soft Electronic Systems

Electrofluids, concentrated suspensions of electrically conductive particles, have recently attracted attention for their potential as soft conductors. In this study, we investigated the influence of morphological differences in 2D filler materials (graphene-like) on the electromechanical properties of glycerol-based electrofluids. Plasma synthesized few-layer graphene (FLG), chemically exfoliated multi-layer graphene (MLG), and bulk graphite were used as 2D fillers, which differed in specific surface area, aspect ratio, and intrinsic stiffness. Results showed that both electrical and mechanical percolation thresholds decreased with increasing filler aspect ratio. The high aspect ratio of the FLG promotes network formation at low filler concentrations, conferring its electrofluids with the lowest electrical (0.16 wt%) and mechanical (0.63 wt%) percolation threshold. Rheological amplitude sweeps revealed a larger linear viscoelastic region for electrofluids containing few-layer graphene, caused by their reduced internal stiffness and higher aspect ratio. This large capacity for storing elastic energy of FLG-electrofluids makes them almost insensitive to uniaxial tensile strain when encapsulated in elastomers, leading to gauge factors below 1, ideal for soft electrical resistors. In contrast, MLG-electrofluids exhibited good sensing properties as strain gauges. The presented study on structure-property relationships helps for rational design of electrofluids with tailored electromechanical properties that can be tuned for different use cases.