Pushing the boundaries of dielectric permittivity in polysiloxanes: polar dipole modifications enable amorphous pyroelectric polymers

Abstract

The main drawback of polymers in a wide range of soft electrical applications is their low dielectric permittivity. The chemical modification of polymers with organic dipoles has been a successful strategy to increase their dielectric permittivity. However, what is the maximum achievable dielectric permittivity by this method? We present four novel polysiloxanes with relative permittivities ranging from 23 to 31 at room temperature (RT), reaching 34 at 40 °C. These are the highest dielectric permittivity values reported for any amorphous filler-free elastomer. Additionally, we derive a universal guiding principle in designing future elastomers, with an ideal trade-off between elasticity and permittivity at an operating temperature of T_g + 60 °C. We further explore the resulting composites with SiO₂ and TiO₂ and show that two glass transitions (T_gs) occur due to the interfacial layer and the bulk phase. The two phases show distinct dielectric behavior, which we demonstrate as useful in achieving pyroelectric materials. The materials exhibit the highest reported pyroelectricity of any crystal-free, fully amorphous polymer with a stable quasi-static pyroelectric coefficient of 3.4 μC m⁻² K⁻¹ at 30 ± 0.5 °C.