SOLID SELF-ASSEMBLED FILMS OF CELLULOSE WITH CHIRAL NEMATIC ORDER ANDOPTICALLY VARIABLE PROPERTIES

Novel, iridescent solid materials may be produced from lyotropic chira l nematic liquid crystalline suspensions of cellulose microcrystallite s in water by simple evaporation. The microcrystallites are colloidall y stable fragments of microfibrils made by controlled acid hydrolysis of low-yield kraft pulp, filter paper or other cellulose sources. When suspensions of these microcrystallites in water are allowed to evapor ate on a flat surface, a film of cellulose is formed in which the micr ocrystallites maintain their chiral nematic orientation. By changing t he electrolyte concentration in the suspensions, the chiral nematic pi tch of the resultant film may be controlled. For films with pitch leng ths in the range of the wavelength of visible light, the films display the optical properties of chiral nematic liquid crystals, most notabl y they reflect circularly polarized light that changes colour with vie wing angle. The films may thus be of interest as components of securit y papers, and as decorative films and pigments.