Cellulose derivatives optical characteristics

Lyotropic liquid crystals are those which occur on the addition of a solvent to a substance, or on increasing the substance concentration in the solvent. There are examples of cellulose derivatives that are both thennotropic and lyotropic. However, cellulose and most cellulose derivatives form lyotropic mesophases. They usually have a characteristic "critical concentration" or "A point" where the molecules first begin to orient into the anisotropic phase which coexists with the isotropic phase. The anisotropic or ordered phase increases relative to the isotropic phase as the solution concentration is increased in a concentration range termed the "biphasic region." At the "B point" concentration the solution is wholly anisotropic. These A and B points are usually determined optically. 

Liquid Crystaiiine Soiutions. Cellulose esters, when dissolved in the appropriate solvents at the proper concentration, show liquid crystalline characteristics similar to those of other rigid chain polymers (9) because of an ordered arrangement of the polymer molecules in solution. Cellulose triacetate dissolved at 30-40 wt% in trifluoroacetic acid, dichloroacetic acid, and mixtures of trifluoroacetic acid and dichloromethane exhibits brilliant iridescence, high optical rotation, and viscosity-temperature profiles characteristic of typical aniostropic phase-containing liquid crystalline solutions (10). Similar observations have been made for cellulose acetate butyrate (11), cellulose diacetate (12), and other cellulose derivatives (13,14). Wet spinning of these liquid crystalline solutions yields fibers... 

In optical device application, biomass-derived cellulose esters are being studied actively as a potential material for optical films. Besides being derived from abundantly available biomass resources, they also possess characteristics suitable as optical films such as high transparency and excellent heat resistance [8]. By virtue of these properties, cellulose esters provide huge possibilities for future development of optical films in order to meet the market demands. 

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