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 (beta) 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 degrees C similar to 150 degrees C) were about 0.2eV, 0.9 similar to 1.5eV and 2.0 similar to 2.5eV. In addition, the dielectric spectrum test was performed on LC composites. Permittivity (epsilon(r)) changed little (3.4 similar to 3.9) in frequency range of 20Hz similar to 10(6)Hz and temperature range -60 degrees C similar to 100 degrees C, but increased sharply when temperature was above 140 degrees C. The values of loss (tan delta) increased sharply in low frequencies (<= 20Hz) and high temperatures (>= 130 degrees C) region. The peak of tand shifts to higher temperatures with frequency increasing and to higher frequencies with temperature increasing.