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We have found that nanoparticles of polyhedral oligomeric silsesquioxane (POSS) can induce vertical alignment in nematic liquid crystal (LC) cells as long as the doped weight percentage of POSS in the LC cells is higher than ∼1%. Such nanoparticle-induced vertical alignment (NIVA) is a very suitable technique for application in the low-temperature fabrication of plastic LC displays. The dynamic process of LC orientation from randomly parallel alignment to vertical alignment was recorded, and it is posited that the POSS NIVA is due to the adsorption of POSS on the inner surfaces of the LC cells. The influence of the POSS concentration on the electro-optical properties and dielectric constant of LC cells was also investigated and the results indicate that LC cells doped with ∼1 wt% POSS provide the best electro-optical performance.

The nanoparticles-induced vertical alignment technique was applied to generate variable liquid-crystal pretilt angles based on doping different concentrations of polyhedral oligomeric silsesquioxane (POSS) nanoparticles in the planar-aligned liquid crystal cells. Competition between the homogeneously aligned polyimide layer and POSS-induced spontaneous vertical alignment domain generated the variable pretilt angle. Experimental results demonstrated that the pretilt angle theta(p) is a function of the doped POSS concentration and can be controlled continuously over the range of 0 degrees