Computer simulations of hard pear-shaped particles

Abstract

We report results obtained from Monte Carlo simulations investigating mesophase formation in two model systems of hard pear-shaped particles. The first model considered is a hard variant of the truncated Stone-Expansion model previously shown to form nematic and smectic mesophases when embedded within a 12-6 Gay-Berne-like potential [1]. When stripped of its attractive interactions, however, this system is found to lose its liquid crystalline phases. For particles of length to breadth ratio k = 3, glassy behaviour is seen at high pressures, whereas for k = 5 several bi-layer-like domains are seen, with high intradomain order but little interdomain orientational correlation. For the second model, which uses a parametric shape parameter based on the generalised Gay-Berne formalism, results are presented for particles with elongation k = 3, 4 and 5. Here, the systems with k = 3 and 4 fail to display orientationally ordered phases, but that with k = 5 shows isotropic, nematic and, unusually for a hard-particle model, interdigitated smectic A 2 phases.2

Pomelo, a tool for computing Generic Set Voronoi Diagrams of Aspherical Particles of Arbitrary Shape

“…The shape of these particles is described by the aspect ratio α and the degree of tapering α θ . By using two Bézier curves forming the bottom and top part of the pear and rotating them around their symmetry axis the surface of the particle is generated (figure 7) [11]. A triangulation algorithm of this surface is implemented within the read file, which allows Pomelo to process pear shaped particles in the generic mode.…”

“…A triangulation algorithm of this surface is implemented within the read file, which allows Pomelo to process pear shaped particles in the generic mode. The position file provides the posi- Systems of hard pear shaped particles (α = 3.0) with different degrees of tapering are generated using Molecular Dynamics (see figure 8) [11]. The statistical distribution of the local packing fractions Φ l for different pear systems (α θ = 3.0, Φ g = 0.48 ; α θ = 3.8, Φ g = 0.50 ; α θ = 6.0, Φ g = 0.54) is shown in figure 9.…”

Self-assembly of twisted, multi-sheet aggregates

“…For the ds (û j ,r ij ) factor of the disc-sphere interaction, the 0 parameter (the potential well-depth of the edge-sphere configuration) was chosen to be two, slightly smaller than the disc-disc potential well-depth at the edge-edge configuration (2.63). The corresponding size parameter was then determined by following the Gaussian overlap approach [26], so that σ 0 ds = 0.748. The disc-sphere energy anisotropy parameter was set to fs / es = 0.2, that is, the spheres were preferentially attracted to the edges of the discs.…”

Computer simulation of bistable switching in a nematic device containing pear-shaped particles

“…This particle shape is used since, following the original arguments of Meyer [2], its mesophases exhibit splay flexoelectricity. The interparticle interactions are implemented using the parametric hard gaussian overlap (PHGO) approach introduced in [19]; we use the parameterisation with elongation k = 5 shown, in Ref. [19], to possess both nematic and smectic A 2 phases, the latter being a bilayer smectic phase with layers formed perpendicular to the director.…”

“…The interparticle interactions are implemented using the parametric hard gaussian overlap (PHGO) approach introduced in [19]; we use the parameterisation with elongation k = 5 shown, in Ref. [19], to possess both nematic and smectic A 2 phases, the latter being a bilayer smectic phase with layers formed perpendicular to the director. Being based on a purely steric single-site interaction, this is a particularly efficient model for use here, though similar behaviour can be expected for any of the generic flexoelectric particle models introduced in recent years [20][21][22].…”