Phase behavior of bent-core molecules

Abstract

Recently, a new class of smectic liquid crystal phases characterized by the spontaneous formation of macroscopic chiral domains from achiral bent-core molecules has been discovered. We have carried out Monte Carlo simulations of a minimal hard spherocylinder dimer model to investigate the role of excluded volume interactions in determining the phase behavior of bent-core materials and to probe the molecular origins of polar and chiral symmetry breaking. We present the phase diagram of hard spherocylinder dimers of length-diameter ratio of 5 as a function of pressure or density and dimer opening angle ψ. With decreasing ψ, a transition from a nonpolar to a polar smectic A phase is observed near ψ=167°, and the nematic phase becomes thermodynamically unstable for ψ<135°. Free energy calculations indicate that the antipolar smectic A (SmAP_A) phase is more stable than the polar smectic A phase (SmAP_F). No chiral smectic or biaxial nematic phases were found.