Nanoparticles dispersed in liquid crystals: impact on conductivity, low-frequency relaxation and electro-optical performance

We study the impact of functionalized gold nanoparticles on the impedance response of nematic nanoparticle/liquid crystal dispersions in the frequency range of 0.1 Hz–100 kHz. By fitting a suitable equivalent electric circuit model to the experimental data we show that nanoparticle doping does not affect the permittivity of the nematic host, but significantly increases its conductivity. This causes a Debye-type relaxation process in the Hz and low kHz regime, which originates from mobile charge carriers accumulating near the electrodes of the test cell. The effect of this electrode polarization on the electro-optical response of the nanocomposites is discussed with respect to threshold voltage and dielectric permittivity. We demonstrate that nanoparticle doping does not alter the electro-optic response at frequencies above the occurrence of electrode polarization, while it strongly deteriorates the performance in the low frequency regime.