Reentrant nematic and multiple smectic-Aliquid crystals: Intrachain flexibility constraints

Abstract

A recent new microscopic, molecular statistical-physics theory for the intrachain constraints on the n-alkyl tail-chain flexibility for molecules composed of rigid rodlike cores and n-alkyl tail chains in the smectic-$A_1$, smectic-$A_d$, and nematic (including reentrant nematic) liquid-crystal phases and the isotropic liquid phase is used to calculate relative stabilities as well as various thermodynamic and molecular ordering properties (including odd-even effects) for these phases. The molecules can interact via these site-site intermolecular interactions: hard (steric) repulsions, various Lennard-Jones (LJ) potentials for soft repulsions and London dispersion attractions, and/or dipolar forces (dipole-dipole and dipole–induced-dipole). The theoretical results in this paper are in significantly better agreement with experiment than are results in earlier papers using older, more approximate theories. The effects of varying pressure, tail-chain flexibility, and intermolecular interactions on the relative stabilities of the multiple smectic-A phases and the reentrant nematic phase are presented. These relative phase stabilities are sensitive to subtle changes in these variables. Predictions and accompanying physical explanations are also made for various systems that have not yet been chemically synthesized and/or studied experimentally.