Study of ion beam alignment of liquid crystals on polymer substrates

Various polymer substrates, including polyimide and polystyrene were bombarded with an Ar+ ion beam in high vacuum at an oblique angle. The alignment direction of the liquid crystal 5CB on these polymer substrates is always parallel to the ion beam propagation direction regardless of the type of polymer used. The alignment mechanism is studied using surface sensitive techniques such as Polarized Attenuated Total Reflection Infrared Spectroscopy (ATR-IR), and X-ray Pholoelectron Spectroscopy. We propose that selective destruction of the weakest bonds (pi bonds) in the polymer by the Ar+ ion beam results in a net excess of the remaining pi bonds. The anisotropy in these pi bonds align liquid crystals parallel to the ion beam propagation direction.