Melting transition temperature side chains, effect

Figure 11.13. Effect of side-chain branching on the melting point and glass transition temperature of...

Liquid crystalline solutions as such have not yet found any commercial uses, but highly orientated liquid crystal polymer films are used to store information. The liquid crystal melt is held between two conductive glass plates and the side chains are oriented by an electric field to produce a transparent film. The electric field is turned off and the information inscribed on to the film using a laser. The laser has the effect of heating selected areas of the film above the nematic-isotropic transition temperature. These areas thus become isotropic and scatter light when the film is viewed. Such images remain stable below the glass transition temperature of the polymer. 

The glass transition temperature of amorphous polymers is a function of the chemical structure of the polymer chain. It varies widely with the types of skeletal atoms present, with the t T)es of side groups, and with the tacticity of side groups along the polymer backbone. Table 14.11 demonstrates the effects of structural variations on the crystalline melting temperature and glass transition temperature for several polymers. 

Crystallization may take place only within the temperature region limited on the upper side by the melting point, T, and on the lower side by the glass transition temperature, T. The crystallization behavior very much depends on the state of miscibility, as well as on the nature of other blend s components. In miscible blends Tg is a monotonic function of the components T s. When the second component is amorphous, its presence can either decrease or increase the tendency of the first resin to crystallize. The process depends on the blending effects on T and on the chain mobility (the free-volume effect). When T of the amorphous component is lower... 

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