Models of Chiral Nematic Cellulosics

Several models are presently used to describe the chiral nematic structure and its temperature dependence for cellulosics. The following behavior has been observed for their supermolecular structure 

Various models proposed may not account for all these experimental facts. The Keating [20] and Bottcher [21] evaluation does not account for such a variety of behavior. Goossens [22] proposed the chiral nematic structure as the result of an anisotropic dispersion energy between chiral mesogens, and predicts for thermotropic LCs a pitch that is essentially independent of temperature. Lin-Liu et al. [23] developed a theory that accounts for all the above-stated temperature effects. The temperature dependence of the pitch is determined by the shape and position of the intermolecular potential as a function of the intermolecular twist 

A statistical model was introduced by Ki-mura et al. [25] which included attractive and repulsive asymmetric intermolecular forces for rod-like molecules. The results are summarized as Eq. (5), which is widely used for the lyotropic chiral nematic state 

Boltzmann constant. This relation fulfills all the experimental observations and leads to the twisting power = 0, if the attraction and steric repulsion cancel. 

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