Memory effect in smectic-A phase of ferroelectric liquid crystal

Abstract

Memory effect has been observed in smectic-A (Sm-A) phase of ferroelectric liquid crystals (FLCs) using dielectric spectroscopy and texture observation. The dielectric relaxation processes in FLC materials with wide range of Sm-A phase and a high electroclinic coefficient have been investigated near the phase transition of Sm-C*-Sm-A phase in thin and planarly aligned cells in the frequency range 10Hz–10MHz. Here phason mode (Goldstone mode) and soft mode contribution in dielectric permittivity could not be clearly separated, near and slightly above the transition temperature Tc. If there is a contribution of phason mode after Tc in Sm-A phase then there is a possibility of getting memory even in Sm-A phase where the molecules get clamped in one direction and stay there even when the field has been removed. A comparative analysis of dielectric permittivity as well as texture in Sm-C* phase has been done on a virgin cell and on a cell in which bias has been applied in Sm-A phase just 1–2°C above Tc for 1min. The difference in dielectric permittivity and texture in the two different conditions clearly shows the continuance of memory effect from Sm-A phase to Sm-C* phase. The effect is probably due to local azimuthal variation in a finite range of Sm-A phase just above Tc.