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Orientation of Liquid Crystal Monolayers on Polyimide Alignment Layers: A Molecular Dynamics Simulation Study

Detailed atomistic molecular dynamics simulations were performed on monolayers of 4′-n-octyl-4-cyanobiphenyl (8CB) adsorbed onto a surface of poly-m-alkanpyromellitimide (poly-m-APM), where m is the number of CH2 units between the imide moieties. Poly-3-APM and poly-4-APM surfaces served as model surfaces to investigate the influence of microscopic grooves, polar carbonyl groups exposed to the surface, and an anisotropic van der Waals interaction between the liquid crystal (LC) molecules and the polymer chains. A Lennard-Jones fluid was chosen as the bulk phase in order to mimic the bulk LC phase. The fluid lubricates the motion of the LC molecules and increases the molecular tilt angle. While microgrooves dominate the alignment of isolated molecules, an anisotropic van der Waals interaction with the main chain is stronger in the case of entire monolayers.