Alignment of Nematic Liquid Crystal by Carbon Nanotube Sheets on Substrates with Hexamethyldisilazane and Silicon Dioxide Co-Adjuvant Layers

Liquid crystal needs alignment layers for achieving a monodomain in which there is one specific orientational direction in a region as large as the aligning surface. The process is easy and well controlled but still needs care for avoiding contaminations that can spoil the alignment. Carbon nanotube (CNT) sheets are an attractive alternative for obtaining alignment of liquid crystal along one direction, which is the nanotube orientation. The degree of alignment of the tubes is however not as high as desirable and some tubes protrude from the common orientation direction, deteriorating the alignment and electro-optic performance of the liquid crystal. The realization of cells based on aligned CNTs in sheets in which the liquid crystal is uniformly and unidirectionally aligned are presented here. For realizing the substrates for the cells it was needed to improve the adhesion of the sheets on the glass surfaces with hexamethyldisilazane (HMDS) and ethanol treatment, and the flatness by using a silicon dioxide (SiO₂) coating. The order parameter S of these CNTs is measured by anisotropic absorption giving a value comparable to the one typical of nematic liquid crystal.