Ionic Liquids as Additives to Improve the Stretchability of Fluorine Rubber/Metal Filler Conductive Elastomers: a Miscibility Study

We report an intrinsically stretchable conductive elastomer containing fluorine rubber and micrometer-sized silver-coated copper fillers, in which ionic liquids were incorporated to improve the performance. The effects of the miscibility between the ionic liquids and fluorine rubber on the stretchability and conductivity of the composites were particularly focused. The miscibility was analyzed by differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS). We compared three different ionic liquids and found that the ionic liquids that are miscible with the rubber can more effectively plasticize the composites to improve the conductivity under stretching, giving a fracture strain more than 400% where the resistance remains below 40 Ω. The effects of the size and shape of the silver-coated copper fillers and the viscosity of the casting solutions were also studied to optimize the performance of the composites. Furthermore, the fluorine rubber was cross-linked to enhance the elastic recoverability of the composites. The cross-linked film shows a fracture strain up to 340% and a good cyclic stretching durability even with the usage of large flakes (15–20 μm) as the conductive fillers.