An Investigation on Novel Dielectric Phenomenon of Thermochromic RTV Composite: Role of Phase Transition

Dielectric properties of thermochromic RTV (room temperature vulcanized silicon rubber) composite were investigated and a novel dielectric phenomenon was explored. It was found that in the temperature range of thermochromism, tand and AC breakdown strength both decreased conspicuously with temperature, whilst those of pristine RTV changed slightly. Phase transition from solid to liquid with temperature during thermochromism was confirmed by DSC (differential scanning calorimeter) and was proposed to be the possible origin of novel dielectric phenomenon. The temperature dependence of tand is explained by a combination of decreased resistance to the reorientation of polar molecules due to collapse of intermolecular force and increased cavity volume due to solid-to-liquid phase transition. Meanwhile, the electric strength of thermochromic fillers decreases with the solid-to-liquid phase transition, facilitating the early breakdown of thermochromic fillers and, consequently, leading to the sharp decrease of AC breakdown strength of thermochromic RTV composite. In comparison, no phase transition was found in pristine RTV with increased temperature, which leads to different temperature dependence of tand and AC breakdown strength from thermochromic RTV composite.