Surface anchoring behavior of 5CB liquid crystal confined between iron surfaces: A molecular dynamics study

To examine the anchoring behavior of 4-n-pentyl-4'-cyano biphenyl (5CB) liquid crystal (LC) on iron surfaces, united-atom molecular dynamics simulations were performed with a similar to 12 nm 5CB film composed of 1000 molecules under confinement between both the atomically-flat surfaces and sinusoidal grooved surfaces. The order parameter of 5CB is enhanced by the grooved surfaces, but diminished by the flat one. In both cases, 5CB molecules away from surfaces tend to align parallel to surfaces and along a certain direction. However, for the 5CB near surfaces, the flat surface yields a random planar anchoring and the grooved surface induces a unidirectional planar anchoring. The diffusion slows down when 5CB is confined between surfaces and the slowing down is mainly concentrated near surfaces, making 5CB solid-like. For the 5CB away from surfaces, the flat surface slows down the diffusion, while the grooved surface accelerates the diffusion, especially along the groove (and the director n) direction. The results provide a full description of the iron-LC interactions at the nanoscale and are important for the understanding of LC behaviors anchoring on surfaces with different morphologies.