Electric Field-Induced Transitions and Interlayer Interactions in Intermediate Smectic Liquid Crystal Phases

Abstract

This thesis presents an investigation into the effects of an external electric field on the three- and four-layer intermediate smectic phases. Experiments were performed using electro-optic techniques; thresholds between phases were measured by studying changes in the effective optical tilt. A quantitative measure of the interlayer interaction constant was obtained from the analysis of field-temperature phase diagrams in several materials, which exhibited the intermediate smectic phases in various degrees of stability. Excellent agreement with theory was observed in the field-temperature phase diagrams of these materials.The effect of adding a chiral dopant to liquid crystal compounds was studied and it was found that the interlayer interaction strength is significantly lower in mixtures with a chiral dopant. These measurements provided quantitative information on the importance of the interlayer interaction, which is only indicated qualitatively by other measurements. Deviations from theory were reported in mixtures with increasing concentrations of chiral dopant, in particular in the nature of the transition from the four-layer phase to the three-layer phase.Interesting behaviour in the thresholds between phases was observed in several liquid crystal mixtures in temperature regions close to the triple point on the field- temperature phase diagrams. Measurements of the thresholds between the intermediate phases revealed an unexpected threshold. Further evidence of this unexpected threshold was presented in the form of results of the temperature dependence of effective optical tilt of the various phases; electric field dependence of the response time; and the transient current that flows upon the reversal of an electric field. These measurements revealed that the unexpected threshold was to a field-induced ferrielectric phase with a larger effective tilt than the three-layer phases.Finally, preliminary results are presented from an investigation into defects that form in the thin films in the antiferroelectric smectic phases, with the aim of studying how the elastic constants may affect the stability of the intermediate phases.

Date of Award	1 Aug 2015
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Helen Gleeson (Supervisor)