Effect of Carbon Fillers on the Surface Resistivity and Mechanical Properties of Silicone Materials

This study investigated the influence of carbon fillers with different morphologies on the physicomechanical and electrical properties of composites based on polyaddition-cured poly(dimethylsiloxane) (PDMS). Conductive carbon black, flake graphite, and reduced graphene oxide (rGO) were introduced individually into the silicone matrix. In addition, selected multicomponent formulations containing conductive carbon black, flake graphite, and a viscosity modifier were prepared. The materials were characterized in terms of density, Shore A hardness, tensile properties, surface resistivity, microstructure, and thermal properties using differential scanning calorimetry (DSC). Conductive carbon black had the most pronounced effect on surface resistivity. At a filler content of 2.5 wt.%, the composite retained its insulating properties, whereas increasing the carbon black content to 5 wt.% reduced the mean surface resistivity to approximately 106 Ω/sq, suggesting that the electrical percolation threshold likely lies between these concentrations. Within the investigated concentration ranges, flake graphite and rGO did not lead to the formation of effective conductive pathways. The incorporation of carbon fillers generally resulted in a reduction in tensile strength and elongation at break, with the most pronounced deterioration in mechanical properties observed for composites containing conductive carbon black. In contrast, flake graphite caused a clear increase in hardness with increasing filler content. DSC analysis showed that conductive carbon black had a strong effect on the enthalpy of the observed thermal transition, while only slightly affecting its characteristic temperature. The results confirm that the electrical and mechanical properties of PDMS composites are strongly determined by the morphology and content of carbon fillers, as well as by their mutual interactions.