Highly Transparent and Long‐Term Stable Dielectric Elastomer Composites Enabled by Poly(ionic liquid) Inclusion

Abstract The demand for high‐performance flexible electronic devices has propelled research toward dielectric elastomer composites that exhibit excellent stretchability, high dielectric constant, exceptional transparency, and enduring stability. Compositing with soft fillers is an emerging method that can increase the dielectric constant of the materials while retaining good flexibility. However, liquid metals inclusion results in opaque composites while liquid electrolytes inclusion brings issues with long‐term stability. In this study, compositing polymeric ionic liquids with elastomeric matrix is proposed to address these requisites. Benefiting from adjustable refractive index, high ionic conductivity, softness, and excellent stability, the prepared dielectric elastomer composites exhibit remarkable transparency, excellent elasticity, and increased dielectric constants. Notably, the composites demonstrate resilience to high temperatures up to 250 °C without compromising dielectric or mechanical properties. Furthermore, the composites retain all properties after prolonged exposure at 80 °C for 6 months, highlighting the potential for sustained performance in real‐world applications. Utilizing the exceptional characteristics of polymeric ionic liquid including dielectric elastomers, strain sensors, and alternating current electroluminescence devices are demonstrated, which also presents excellent stability over prolonged use, emphasizing the reliability and long‐term stability of the composites, and showcasing potentials for multifaceted applications in flexible electronics.