A method for improving contrast ratio of polymer dispersed liquid crystal film using the oriented azo-dye molecules in polymer matrix

An improvement in the contrast ratio (CR) of transmittance characteristic of polymer dispersed liquid crystal (PDLC) was achieved by doping the polymer matrix with azo-dye and then orienting the dye molecules with the photo pumping technique. The contrast ratio was measured by the light scattering technique. We investigated the optimum conditions for the scattering characteristics of the dye-doped PDLC films as a function of the dye concentration, of the UV curing intensity, and of the micro-droplets size. The light scattering characteristics of PDLC films with aligned dye molecules are compared with films with dyes randomly oriented. Experimental results indicate that the contrast ratio of these aligned films are much higher than those with nonaligned dye-doped PDLC films. The scattered light in the transparent mode was reduced by factor of 5 at the scattering angle of 10°.