Highly Anisotropic Carbon Fiber Electrodes for DEAs and Their Dynamic Non-Monotonic Conductive Properties

A common method for creating compliant electrodes for dielectric elastomer actuators (DEAs) and soft sensors is to incorporate electrically conductive carbon particles into a polymer matrix. However, using unidirectional aligned carbon fibers instead not only forms a conductive network but also results in a highly mechanically anisotropic electrode. While there is ongoing research to explain the dynamic non-monotonic conductivity-strain behavior of particle-based percolative systems, the mechanics of fiber-based percolative systems have not been thoroughly investigated. Therefore, this work aims to characterize fiber- and fiber-particle-based electrodes. The study reports a counter-intuitive finding that the dynamic behavior of a purely fiber-based electrode is opposite to that of a particle-based electrode. Specifically, while the conductivity of conventional particle-based electrodes decreases when strained, fibrous electrodes generally increase their conductivity with rising strain. This phenomenon may be attributed to the compressive stress experienced by the fibers when the electrode is strained perpendicular to them, resulting in buckling and increased undulation of the fibers, which in turn leads to a higher number of contact points within the network. A more comprehensive understanding of this phenomenon could enable the adjustment of percolation systems that rely on fibers and particles to produce conductors with consistent conductivity within a specific range of strain.