Glassy relaxation in de Vries smectic liquid crystal consisting of bent-core molecules

TL;DR

This study investigates a bent-core liquid crystal exhibiting de Vries smectic behavior, glass transition, and fragile glassy dynamics, revealed through dielectric spectroscopy and phase transition analysis.

Contribution

It provides experimental evidence of de Vries smectic phase and glassy dynamics in a bent-core liquid crystal, highlighting novel dielectric relaxation behavior.

Findings

Presence of de Vries SmA phase with negligible layer contraction.

Observation of a glass transition at 271 K.

Dielectric relaxation follows Vogel-Fulcher-Tammann behavior.

Abstract

We report the experimental investigations on a liquid crystal comprised of thiophene-based achiral bent-core banana shaped molecules. The results reveal the presence of a short range nematic phase at high temperatures and a long-range SmA phase at lower temperatures, which transits to a SmC phase on further cooling the sample. Practically no layer contraction was observed across the SmA to SmC transition, indicating the de Vries nature of the SmA phase. Interestingly, the crystallization does not occur on cooling the sample till 223 K; instead, a glass transition at 271 K was observed. The dielectric spectroscopy studies carried out on the sample reveal the presence of a dielectric mode whose relaxation process is of the Cole-Cole type. The relaxation frequency of the mode was found to drop rapidly with decreasing temperature, further confirming the glassy behavior. The variation of relaxation frequency with temperature follows the Vogel-Fulcher-Tammann equation indicating the fragile glassy nature of the sample.