Increasing the rewriting speed of optical rewritable e-paper by selecting proper liquid crystals

The effect of interaction between liquid crystal (LC) and photoalignment material on the speed of optical rewriting process is investigated. The theoretical analysis shows that a smaller frank elastic constant K₂₂of liquid crystal corresponds to a larger twist angle, which gives rise to a larger rewriting speed. Six different LC cells with the same boundary conditions (one substrate is covered with rubbed polyimide (PI) and the other with photo sensitive rewritable sulfuric dye 1(SD1)) are tested experimentally under the same illumination intensity (450 nm, 80 mW/cm²). The results demonstrate that with a suitable liquid crystal, the LC optical rewriting speed for e-paper application can be obviously improved. For two well known LC materials E7 (K₂₂is larger) and 5CB (K₂₂is smaller), they require 11 s and 6 s corresponding to change alignment direction for generating image information.