Computer simulation of apolar bent-core and rodlike molecules

Abstract

Bent-core molecules have received much interest due to their biaxiality and novel phase ordering. It is, therefore, of interest to model the characteristic shape of these molecules and observe the effect on liquid crystal mesophase formation in a computer simulation study. A simple model of the interaction employed a two-site Gay-Berne potential with the sites separated by +/-0.5 reduced units for all models. The angle between the two sites, 180 degrees -gamma, was varied from gamma=0 degrees to gamma=70 degrees and influenced the phase behavior markedly. The rodlike model formed isotropic, nematic, smectic-A, and smectic-B, phases. Results for the bent-core models show that as the angle gamma increases the transition temperature to the ordered phase decreases. As gamma increases the nematic phase is first destabilized then stabilized with respect to the smectic phase and a tilted smectic-B phase is seen at gamma=20 degrees. For gamma=40 degrees a "TGB-like" phase is identified as the system cools whereas for gamma=70 degrees no ordered phase is formed.

Computer Simulations of Biaxial Nematics

“…Moving to attractive-repulsive potentials, similar results have been obtained with the GB models simulated by Memmer [133] and Neal and coworkers [134,135] who performed NPT MC simulations of rigid bent-core dimers with aspect ratio 1 : 1 : 3 and various apex angles. The isotropic to N u transition temperature was found to decrease reducing the aperture angles.…”

“…Even for this GB model, the N u phase disappeared for an intermediate 170 degrees apex angle. Interestingly, close to the nematic-smectic phase transition a spontaneous chirality symmetry breaking [136] was reported [133,134,137] to produce organisations related to those predicted by Lubensky and Radzihovsky [4], or observed by Görtz and Goodby [19]. The presence of a central transverse dipole [135] suppresses the N u phase to give transitions from isotropic to smectic phases, and this is at variance with results from atomistic simulations (see later on).…”

“…[46] reports N b mesogens with 90 degrees aperture). Certain intermediate apex angles destroy the N u [131,134,135]. To provide a N b phase a bent molecular shape is not sufficient, and other interactions terms (e.g.…”

Phase ordering of zig-zag and bow-shaped hard needles in two dimensions

“…33 A plethora of models have thus been devised to understand the three-dimensional bulk behavior of these systems. [40][41][42][43][44] Yet relatively little theoretical attention has been paid to related models in two dimensions. [45][46][47] Here, we consider the two-dimensional phase behavior of a bent-needle model in both its chiral zig-zag and achiral bow-shaped configurations (Fig.…”

Biaxial phases of bent-core liquid crystal polymers in shear flows

“…A possible reasoning by Johnson et. el [22] in the numerical simulations of a cluster of VLCPs with Gay-Berne potential is as follows: at low shear, a higher value of bentangle, lowers the "length-to-breadth" ratio of the V-shaped molecules, which in turn increases the "packing density" of these molecules in a given monodomain. This increase in "packing density" leads to a physically unfavorable configuration, and hence a higher free-energy density.…”