Phase transitions in nanofilms of polar smectic liquid crystals with multilayer periodicity

Abstract

Optical investigations and calculation of structures were performed on films of liquid crystal with the sequence of phase transitions in the bulk sample $\mathrm{Sm}{C}_{A}^{*}\ensuremath{-}\mathrm{Sm}{C}_{d3}^{*}\ensuremath{-}\mathrm{Sm}{C}_{d4}^{*}\ensuremath{-}\mathrm{Sm}{C}^{*}\ensuremath{-}\mathrm{Sm}{C}_{\ensuremath{\alpha}}^{*}\ensuremath{-}\mathrm{Sm}A\ensuremath{-}I$. We investigated freestanding nanofilms with number of smectic layers from 2 to 6 with thickness commensurate, smaller, or greater than the period of $\mathrm{Sm}{C}_{d3}^{*}$ and $\mathrm{Sm}{C}_{d4}^{*}$ phases of the bulk sample. The number of phase transitions increases as the film thickness increases. Under temperature change the transitions occur with conservation as well as with change of the direction of film polarization with respect to the molecular tilt plane. In thick films at high temperature the film can be switched by electric field from the state with longitudinal (parallel to the molecular tilt plane) into a state with transverse (perpendicular to the molecular tilt plane) electric polarization. In the framework of Landau theory of phase transitions, structures and phase transitions in the bulk sample and in nanofilms were calculated; values of interlayer interactions were estimated. The molecular structure was assumed to be planar with different sequences of synclinic and anticlinic orderings in nearest layers. The results of calculations are in good agreement with experiment.