Thermally stimulated current and dielectric studies of liquid crystal composites

Recently, composite materials of liquid crystal polymer (LCP) and inorganic filler attracted the attention of the electrical industry. In this research, the relationships between thermally stimulated current (TSC) of liquid crystal (LC) composites and the polarization temperature (T_p), polarization voltage (V_p) and heating rate (β) were investigated respectively. The variation of trap levels and trapped charges under different experimental conditions were calculated and analyzed. Trap levels of the peaks in temperature range (-60°C~150°C) were about 0.2eV, 0.9~1.5eV and 2.0~2.5eV. In addition, the dielectric spectrum test was performed on LC composites. Permittivity (ε_r) changed little (3.4~3.9) in frequency range of 20Hz~10⁶Hz and temperature range -60°C ~100°C, but increased sharply when temperature was above 140°C. The values of loss (tanδ) increased sharply in low frequencies (≤ 20Hz) and high temperatures (≥ 130°C) region. The peak of tanδ shifts to higher temperatures with frequency increasing and to higher frequencies with temperature increasing.