Anomalous Temperature-dependent Dielectric Performance of Thermochromic RTV Composite: Role of Phase Transition

The temperature dependence of relative permittivity (εr), dissipation factor (tan δ) and AC breakdown strength of thermochromic room temperature vulcanized (RTV) silicone rubber composites are investigated in this work. It is shown that, in the thermochromic process, increased temperature leads to distinct decrease of tan δ and AC breakdown strength of the composites, which is proposed as anomalous temperature dependence of dielectric performance. The solid-liquid phase transition in the thermochromic process, which is confirmed by DSC results, is suggested to be the origin of this particular behaviour. With enhanced temperature, the solid-liquid phase transition causes the collapse of intermolecular force and enlarged cavity volume of core material in thermochromic microcapsules, leading to reduced dissipation in the reorientation of polar molecules and, therefore, decreased tan δ. Moreover, due to solid-liquid phase transition, both the AC breakdown strength of thermochromic microcapsules and that of composites can be lowered.