| Liquid Crystal Displays, LCDs are ubiquitous. At the heart of the display is a polymer film which is used to uniformly align the liquid crystal over large areas---the dimensions of the LCD itself. First generation alignment layers consist of rubbed PI films fabricated by a mechanical rubbing process which produces dust and mechanical damage that is not consonant with clean room fabrication. Furthermore, the mechanism of liquid crystal alignment on rubbed surfaces is poorly understood. The ability to understand the alignment mechanism and develop novel alignment layers may lead to more efficient devices and manufacturing processes.In this work we employed soft lithography as an alternative fabrication method of liquid crystal alignment layers. We study the mechanism of liquid crystal alignment on polymer films with variable feature dimensions. One dimensional line gratings were used to examine the mechanism of liquid crystal alignment on rubbed surfaces. We determined that the physical topography is sufficient to align the liquid crystal director however, the chemical interaction between the mold and the alignment layer during fabrication can affect the orientation of the director. If this fabrication method is to be used, either the mold should be removed in a manner that reinforces alignment induced by the surface topography, or the mold and alignment layer chemistry must be optimized to prevent any unwanted interactions. We also fabricated alignment layer features exhibiting four-fold (square and rectangular patterns), six-fold (triangles in a hexagonal array), and five-fold (Penrose aperiodic patterns) symmetries. We observed multi-stable alignment on such surfaces and observed that pattern features less than 100nm tall and about 500nm in- plane width have the best optical uniformity. |
