Liquid crystal and cellulose derivatives composites used in electro-optical applications

We have performed a preliminary study by light transmission of the electro-optical behaviour of several cells prepared either from hydroxypropylcellulose (HPC) or HPC with cellulose acetate (CA) (1% w/w) cross linked in both cases with 1,4-diisobutanocianate (BDI) (7%w/w) and different concentrations of a commercial nematic liquid crystal mixture with varying optical anisotropies. The optical response when the cells are subjected to a short ac electric pulse of variable intensity is presented and correlated with the use of CA and the optical anisotropy of liquid crystal mixture used in the cells, it was found that cells with CA exhibit much larger contrasts but also a small decrease of the maximum light tr;transmission when compared with cells without CA. The anisotropy of the liquid crystal mixture is seen to have a strong influence on the electro-optical behaviour of the cells prepared with CA. From scanning electron microscopy (SEM), we found in the surface of the solid films prepared with CA some heterogeneities and porous (2 mu m) that can be responsible for the strong increase in the contrast observed.