Liquid crystal alignment by polyhedral oligomeric silsesquioxane (POSS)-polyimide nanocomposites

Abstract

Polyimide (PI) films are widely used in the liquid crystal display (LCD) industry to align liquid crystal (LC) molecules in a specific orientation with a pretilt angle 0(p) on the PI alignment films. It was observed that physical dispersion of polyhedral oligomeric silsesquioxane (POSS) nanoparticles in commercial homogenous PIs decreases the surface energy of the PI alignment films and generates a controllable 0(p) in the range 0 degrees < 0(p) < 90 degrees, which is not easily achieved by complicate PI synthesis. Characteristics of POSS-PI nanocomposites were studied to investigate the influence of FOSS nanoparticles on PIs. Increased absorption in the infrared spectra and decreased decomposition temperature and glass transition temperature with POSS doped concentration in PI were observed due to the increase in free volume of POSS-PI nanocomposites. Such nanoscale hybridization suggests a novel approach to tune the properties of PIs through modification of molecular interaction. A fast response no-bias optically-compensated bend (OCB) LCD with a pretilt angle of 68 degrees was also demonstrated in this work. (C) 2013 Elsevier B.V. All rights reserved.