Non-linear behaviour of phason mode with bias field in ferroelectric liquid crystals

Abstract

The decrease in Goldstone mode relaxation frequency with applied dc electric field in a deformed helix ferroelectric liquid crystal (DHFLC) is observed at room temperature. This decrement in relaxation frequency is observed at very low dc electric fields (below the threshold voltage, i.e. around 2 V). This behaviour is compared with that of conventional ferroelectric liquid crystals (FLCs) where the relaxation frequency increases with the applied dc electric field. It is observed that a low dc electric field is insufficient to unwind the helix completely due to the higher rotational viscosity of the DHFLC material. Moreover, the DHFLC molecules take more time in the winding (Smectic C–Smectic C*) process, compared to the FLC molecules, which take comparatively less helix winding time because of their low viscosity. The decrease in relaxation frequency in DHFLCs with bias has been attributed to the critical balancing amongst the electric torque, elastic constraints and rotational viscosity in a certain regime of the electric field not exceeding the threshold field.