Ordering, clustering, and wetting of hard rods in extreme confinement

Abstract

The effect of out-of-plane orientational and positional fluctuations is examined in the phase behavior of hard spherocylinders confined between two parallel walls. The stability of isotropic, nematic, and solid phases is studied for aspect ratios (κ = 1 + L/σ , where σ and L are the diameter and length of the cylinder) of 8, 10, and 16, while the width of the slitlike pore, H , is set in the quasi-two-dimensional regime, σ < H 2σ. Using replica exchange Monte Carlo (REMC) simulations and Onsager theory we provide evidence for the stabilization of the nematic order with increasing pore width. The minimum surface density necessary to exhibit nematic order remains nearly the same with increasing H , while the upper bound of nematic order is postponed to higher densities in detriment of the single-layer-solid phase. We prove that a drying-out effect takes place in the pore as the density increases linearly from the wall to the middle of the pore in the ideal gas limit. This behavior is kept for the isotropic phase and partially in the nematic one, while a wetting behavior is observed at the walls mostly for the solid phases. For κ = 8, we have also observed a compressibility signal of a transition between an isotropic fluid and a cluster-like fluid. This cluster phase is destabilized by increasing H. Finally, we build a master diagram, where the drying-wetting, solid-solid, and close packing density curves are independent from κ.

Connectedness percolation in the random sequential adsorption packings of elongated particles

“…For non-mesogenic particles with small aspect ratios (ε < 3) in the extreme confinement limit -small distances between the walls (h/d ≤ 2), a structural transition from a planar (particle's long axis parallel to the walls) to a homeotropic (particle's long axis perpendicular to the walls) layer with increasing density was observed [37]. For hard discorectangles between the two parallel walls in strongly confined systems (1 < h/d ≤ 2), a rich phase behavior with dependence on the value of the particles' aspect ratio has been observed [38]. For hard ellipses in a circular cavity, the formation of oriented layers in the vicinity of the wall was also reported [39].…”

Topological fine structure of smectic grain boundaries and tetratic disclination lines within three-dimensional smectic liquid crystals

“…The most prominent type of ordering, which is typically found in liquid crystals, is orientational (nematic) ordering, where the characteristically shaped subunits, i.e, molecules or colloidal particles in close proximity, show a tendency to align. If this preferred order gets frustrated, e.g., by confinement to a finite container [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49], constraining on a surface [50][51][52][53][54][55][56][57] or insertion of obstacles [58][59][60][61][62][63][64][65][66][67], topological defects emerge, which are discontinuities in the ordered structures that can display particlelike properties themselves [6,16,[68][69][70]. * Rene.Wittmann@hhu.de FIG.…”

Phase Transitions and Hysteresis for a Simple Model Liquid Crystal by Replica-Exchange Monte Carlo Simulations

“…This method is widely applicable and has been used for a diverse range of system types, such as hard spherocylinders [ 21 ], small mercury clusters [ 22 ], Glutamine Amides [ 23 ], and water confined within nanotubes [ 24 ]. The isothermal-isobaric replica-exchange algorithm inhibits kinetic trapping problems and, as such, can be used to greatly reduce or even eliminate hysteresis.…”