Role of the order parameter, electric field, and geometric confinement on the dynamics of the photoinduced Nematic-Isotropic transition

Abstract

We investigated the dynamics of photoinduced nematic-isotropic transition especially the back relaxation time and its influence on three different parameters. The parameters are (a) Order parameter: the temperature dependence of the response time was calculated in a material exhibiting a photostimulated isothermal Nematic-Isotropic transition. Using a simple description we show that the temperature dependence of this response time can be understood in terms of the order parameter excess between the equilibrium and photostimulated states. (b) Electric field: application of an electric field accelerates the recovery of trans isomers from the photoinduced cis isomers. An important consequence of this effect is the rapid return of the equilibrium nematic phase from the photo-driven isotropic phase of liquid crystals. (c) Confinement: by confining liquid crystals in an in situ created network of aerosil particles. The DSC scans taken at slower rates for a particular composite in the soft gel regime have a two-peak profile across the N-I transition. In contrast, the bulk has a single peak at all rates investigated. The double peak profile is associated with a crossover from random-dilution to random-field regime. The dielectric measurements, which are the first such measurements on the photoisomerization-driven isothermal phase transitions in LC-aerosil composite bring out several interesting features including the dependence of the photo-driven shift in the transition temperature and the response time on the concentration of aerosil.