Landau Theory of Liquid Crystalline Phases

TLDR: In this article, the phenomenological theory of phase transitions in liquid crystals, the so-called Landau-De Gennes theory, is applied to the nematic-isotropic transition.

Abstract: In this chapter we deal with the phenomenological theory of phase transitions in liquid crystals, the so-called Landau-De Gennes theory. First of all the basic ideas of the Landau theory are discussed. The theory is then applied to the nematic-isotropic transition. Attention is paid to two pretransitional effects, namely induced birefringence or the Cotton-Mouton effect and light scattering. This latter phenomenon is calculated in terms of fluctuation theory. Next we discuss the smectic A-nematic phase transition. This transition is described first in terms of one order parameter: the amplitude of a density wave. The result is a second-order transition. We then show that the second-order character can be changed into a first-order one by incorporating either the influence of the amplitudes of other density waves or the effect of the orientational ordering.