Nonlinear Dielectric Response of the Liquid Crystal 8CB near the phase transitions

The nonlinear dielectric response of the liquid crystal (LC) 8CB (4'-octyl-4-cyanobiphenyl) was measured near the smectic-nematic and nematic-isotropic phase transitions. The sample was filled in a commercially available LC capacitor cell of dimensions (1 cm $\times $ 1 cm $\times $ 9 $\mu $m). The cell was mounted in a temperature-controlled environment with a stability and resolution of 1 mK. The capacitance of the cell was measured at different temperatures in the range 25 -- 45\r{ }C covering both phase transitions, and over a range of frequencies up to 100 kHz, and a signal level in the range of 0 -- 5V, using a lock-in amplifier (SRS830) and LCR meter (Fluke PM6304). Nonlinear effects were observed in the capacitance even at a 200 mV signal level, and very large changes in the capacitance, both linear and nonlinear, were observed in the nematic phase, near each phase transition. *Undergraduate physics students **Recent physics graduates