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

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 θp 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 θp in the range 0° < θp < 90°, which is not easily achieved by complicate PI synthesis. Characteristics of POSS–PI nanocomposites were studied to investigate the influence of POSS 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° was also demonstrated in this work.

► Pretilt angle of liquid crystal can be tuned by POSS–polyimide nanocomposite films.
► Increased IR absorption was observed in PI–POSS nanocomposite films.
► Decreased decomposition temperature was observed in PI–POSS nanocomposite films.
► Decreased glass transition temperature was observed in PI–POSS nanocomposite films.
► A no-bias OCB LCD was demonstrated using PI–POSS nanocomposites alignment films.