Thermodynamics and kinetics of the phase transition ferroelectric smectic C* - nematic in electric fields

Abstract

The phenomenological theory for the first order phase transition chiral smectic C-chiral nematic is developed. It is predicted that the transition temperature T _CN can depend on the LC cell thickness d. The polar interactions of molecules with the solid surface of the cell lead to the increase of T _CN with decrease of d, whereas Van-der-Waals interactions will dominant in very thin cells and the decrease of T _CN at the decrease of thickness is expected.

The kinetics of the phase transition S_C* - N under the influence of electric field is considered as a growth of smectic C nuclei in a supercooled nematic phase, where the degree of supercooling ΔT is proportional to the electric field E and to the closeness to the thermodynamical transition point T _CN. The probability of the smectic nuclei formation and the rate of their size increase with time is described on the basis of classical theory of nuclei formation.

The behaviour of the smectic C nuclei in dependence on cell thickness and on kind of electric field is analysed and experimental data are interpreted. The processes of diffusion and coalescence of nuclei and of melting the induced S_C* phase after switching off the electric field are discussed.