No abstract

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 pretilt angles of liquid crystal molecules can be controlled by using conventional polyimide (PI) alignment material doped with different concentrations of Polyhedral Oligomeric Silsequioxanes (POSS) nanoparticles, which have been observed to spontaneously induce vertical alignment. The addition of POSS in the homogenous PI changes the surface energy of the alignment layer and generates a variable pretilt angle. Experimental results demonstrate that the pretilt angle thetap is a function of the POSS concentration, and can be tuned continuously over the range of 0 degrees

A simple method to make a switchable liquid crystal (LC) Fresnel lens with high diffraction efficiency and a low driving voltage was proposed based on the photo-induced surface modification of the vertical alignment layer. UV illumination alters the pretilt angle of alignment layers, a Fresnel zone-distribution hybrid alignment in the homeotropic LC cell can be straightforwardly achieved through UV exposure, yielding a concentric structure of the Fresnel phase LC lens. A remarkable diffraction efficiency of ~31.4%, close to the measured diffraction efficiency of the used Fresnel-zone-plate mask of 32%, was detected using a linearly polarized incident beam.

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