Computer simulation of interactions between liquid crystal molecules and polymer surfaces - I. Alignment of nematic and smectic A phases

Results are presented from computer simulations of liquid crystal molecules in contact with polymeric surfaces. These form part of a study of the comp lex alignment interactions which operate in liquid crystal displays. The li quid crystal molecules considered are 4-n-pentyl-4'-cyanobiphenyl (5CB) and 4-n-octyl-4'-cyanobiphenyl (8CB); the polymeric surfaces simulated were cr ystalline polyethylene, polypropylene, poly(vinyl alcohol) and Nylon 6. Add itional simulations were performed using graphite as a substrate. Polyethyl ene, poly(vinyl alcohol) and Nylon 6 were all found to induce orientation o f the 5CB and 8CB molecules parallel to the polymer chain axes, as would be expected from experimental studies. On the other hand, polypropylene induc es many different orientations with no clear preference for either. No evid ence was found for the alignment of 8CB molecules on graphite substrates, i n disagreement both with experimental findings and the results from previou s simulations. The nature of the alignment interactions and possible reason s for the observed discrepancies are discussed.