Interplay between Mechanical Fatigue and Network Structure and Their Effects on Mechanical and Electrical Properties of Thin Silicone Films with Varying Stoichiometric Imbalance

Thin silicone films for applications as dielectric electroactive polymer (DEAP) are fatigued under mechanical cycling (Wöhler tests) until rupture. The silicones are based on linear vinyl‐terminated poly(dimethylsiloxane) (PDMS) cross‐linked with tetrafunctional methylhydrosiloxane–dimethylsiloxane copolymer. Stoichiometric imbalance of the hydrosilane to vinyl groups is varied (1.3, 1.7, and 3). Complementary, all silicones are compounded with silicone oil (55 wt%) and silica (4.5 wt%). Changes in cross‐linking density, elastic modulus, dielectric permittivity, and dielectric breakdown are examined. The fatigued specimens show increased cross‐linking density due to mechanically induced secondary cross‐linking of excessive hydrosilane groups. This leads to significant changes in the elastic modulus and permittivity of the material, which can negatively affect the performance of the DEAP device. The “critical loading conditions,” where the fatigued specimens show maximum changes in properties, are found to depend on excess hydrosilane content. Mechanical fatigue results in an increase in cross‐linking densities due to the mechanically induced secondary cross‐linking of excessive hydrosilane groups. This leads to significant changes in elastic modulus and permittivity of the material, which can degrade the performance of dielectric device. The breakdown strength of fatigued specimens is found to be generally lower after mechanical fatigue.