Influence of solvent on the piezoresistive properties of carbon-particle-filled elastomers

Carbon particle-filled elastomers are a highly researched class of materials and serve as soft, stretchable conductors for a number of potential applications ranging from dielectric elastomer actuator electrodes to resistive stretchable sensors. In order to lower the viscosity of uncured carbon particle-filled elastomer mixtures, solvents are regularly used in many manufacturing processes described in literature. However, the influence of these solvents on the resistivity has only been investigated with regard to further processing steps such as inkjet or screen printing but not the bulk material itself. In addition, a common assumption is that the solvent will fully evaporate during the curing process without any effect on the final properties. To address these knowledge gaps, the resistance and solvent evaporation of carbon particle-filled silicones are tracked during curing. The investigated parameters include the curing temperature, thickness of the samples and solvent type. Depending on the solvent type, the evaporation rates and resistivity curves differ significantly. In addition, static impedance spectroscopy measurements are performed to assess the frequency-dependent resistivity after curing and the solvent’s effect thereon. Interestingly, a lack of solvent leads to a non-conductive material while samples with added solvent and same silicone and carbon particle content are conductive. Similarly, the piezoresistive effect of the materials also differs, which makes the type and existence of solvents an important parameter to consider for manufacturing conductive elastomers.