Solidified liquid crystals of cellulose with optically variable properties

A solidified liquid crystal cellulose film of crystal particles of colloidal dimensions, of native cellulose I, in helicoidal arrangements exhibiting a chiral nematic pitch of about 0.25 .mu.m to 0.6 .mu.m, said film having a coloured iridescent appearance and reflecting left-circular polarized light to provide reflected light in the visible spectrum from violet to red;

• said helicoidal arrangements having their chiral nematic axes perpendicular to a surface of the film and said cellulose crystals having their long axes mostly parallel to said surface;
• said film displaying the following characteristics:
• a) reflection of light by constructive interference with the reflected wavelengths of light changing with viewing angle in accordance with Bragg's Law;
• b) left-circular polarization of reflected light and reflection of incident left-circular polarized light as left-circular polarized light;
• and
• c) optical activity resulting in rotation of transmitted plane-polarized light.

A process for producing a solidified liquid crystal cellulose film comprising:

• hydrolyzing a particulate natural cellulosic material with acid,
• recovering a stable colloidal dispersion of crystal particles of native cellulose I in a concentration from about 1% to 20% w/w,
• allowing said crystal particles to form a chiral nematic liquid crystalline phase in said dispersion,
• casting said dispersion as a wet film on a planar support, and
• drying said wet film to provide said solidified liquid crystal cellulose film on said support, said film exhibiting a chiral nematic pitch of 0.1 .mu.m to 1 .mu.m.