Computer simulation of liquid-crystal surface modification

– Metropolis Monte Carlo simulations are used to study the interplay between two different anchoring effects of spherocylinders on a modified surface consisting of hard walls onto which liquid-crystal molecules have been perpendicularly grafted. By varying both the length and grafting density of the surface molecules, a number of different and novel anchoring regimes are observed including: planar, homeotropic, tilted and decoupled planar. Introduction. – Much of liquid-crystal science focuses on the anchoring properties of the liquid on solid substrates [1–5]. The interest comes both from the desire to generate anchorings and director profiles that are technologically useful, and from the complexity of the interactions that can be studied [6]. Many methods exist for changing the anchoring properties of a system [7]. In this paper, the focus is on modifying a surface that gives planar anchoring by grafting onto it short alkyl chains that promote homeotropic alignment, a system which has been studied experimentally [8]. We aim to investigate the interplay between competing anchoring behaviours of this kind by performing simulations of a highly simplified model system of rod-like hard particles. The paper is organised as follows. In the following section we present the computational details and molecular models that we use to simulate the liquid crystal and the modified surface. Simulation results are presented consisting of density, director, order parameter and biaxiality profiles for the modified systems. Finally, concluding remarks are given. Molecular model and simulation methods. – The molecular model employed here reduces the physical system to its minimal constituent parts, the aim being to allow changes in the director orientation to be monitored through careful modification of the surface. Although the system of experimental interest is thermotropic, we chose to use hard spherocylinders for both the liquid-crystal model and the surface chains. The spherocylinder model is characterised by the length L of the cylindrical section between hemispherical caps, and the diameter D. The