The Pseudocritical Concept in the Landau Theory of the Nematic—Isotropic Phase Transition

Abstract

An extension of the scalar order parameter Landau-deGennes model for the pseudocritical theory of fluid phase transitions is used to describe pretransitional phenomena in the vicinity of the nematic—isotropic transition. The quantitatively different pretransitional behaviour of fluids near critical points and near simple spinodal points is taken into account. Using temperature, pressure and specific volume as variables, the expression for the Gibbs free energy yields the equation of state and mean-field values of pseudocritical exponents which satisfy the scaling equations. The temperature dependence of some thermodynamic quantities is obtained. The correlation length for the correlation function of scalar order parameter fluctuations is given as a function of temperature. The Ginzburg criterion is used to demonstrate two kinds of crossover behavior.

Key Words:

• nematic liquid crystal
• phase transition
• spinodal
• pseudocritical theory