Computer simulations of interactions between liquid crystal molecules and polymer surfaces II. Alignment of smectic C-forming mesogens

Computer simulations have been performed to examine the behaviour of the li quid crystalline molecule 4-n-heptyl-2-fluoro-phenyl 4-n-octyloxybiphenyl-4 '-carboxylate (MBF) when in contact with crystalline polymer surfaces. The simulations form part of a study of the alignment interactions that are fou nd in liquid crystal displays. MBF forms several smectic phases including a chiral smectic C* phase when suitably doped. In this paper we examine the way that layers of MBF molecules interact with the structure of the crystal line polymer surface, with the aim of understanding how molecular level int eractions give rise to macroscopic phenomena such as the cone angle in ferr oelectric liquid crystal devices. Molecular dynamics simulations consisting of a fixed crystalline polymer surface in contact with either a single MBF molecule or up to two layers of them (48 molecules) have been performed. A variety of simple polymer surfaces have been examined and the simulations show that the cone angle is highly dependent on the geometry of both the li quid crystal molecule and the polymer substrate. For molecules of MBF on po lyethylene substrates, a cone angle of 20 degrees is predicted, in line wit h experimental findings.