Structure-Liquid Crystalline Property Correlations

Although liquid crystallinity is a phase characteristic and not a molecular property, some structural features are well assessed as being conductive to liquid crystal phase formation. Common to all these substances is the asymmetry of molecular shape that produces orientation-dependent interac- 

2 Main Chain Liquid Crystalline Semiflexible Polymers 

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A simple example of how molecular electronic structure can influence condensed phase liquid crystalline properties exists for molecules containing strongly dipolar units. These tend to exhibit dipolar associations in condensed phases which influence many thermodynamic properties [29]. Local structural correlations are usually measured using the Kirkwood factor g defined as... 

Many researchers have reported the structure-thermal property correlations in LCPs from substituted hydroquinones (HQs) and dicarboxylic acids. Lenz and co-workers have investigated the liquid crystallinity of the polyarylates obtained from substituted HQs and terephthalic acid (TA) [6-10], substituted HQs and l,10-bis(phenoxy)decane-4,4/-dicarboxylic acid [8], and substituted HQs and a,oo-bis(phenoxy)alkane-4,4/-dicarboxylic acid [11], Kricherdorf and Schwarz [12] and Osman [13] reported the liquid crystallinity of the polyarylates obtained from substituted HQs and 1,4-cyclohexanedicarboxylic acid, while Krigbaum el al. [14], Heitz and co-workers [15] and Kricherdorf and Engelhardt [16] investigated the liquid crystallinity of the polyarylates synthesized from substituted HQs and substituted TAs. In addition, Jackson reported the liquid crystallinity and the moduli of fibers and injection molded specimens of the polyarylates... 

Liquid crystalline phases also seem to play an important role in topical and transdermal drug delivery. As discussed above, the protective properties of the stratum corneum seems to depend on the properties of its lipid fraction. More specifically, these have been found to form lamellar structures (169, 170), which could be expected to reduce the transdermal penetration of drugs, as well as water evaporation. On the other hand, the presence of Azone may induce reversed-type phases (172). Thus, the generation of oil and water channels seems to correlate with the commonly observed enhanced transdermal penetration of drugs caused by this penetration enhancer (186). 

Our intent, as mentioned earlier, is not to review all the studies concerned with liquid crystalline fluids but to compare their properties with flexible chain polymers, interpret their properties in terms of the domain structure, and look for correlations between flow characteristics and processing conditions. We first examine the behavior of liquid crystalline copolyesters in steady shear flow and in small strain dynamic oscillatory flow. 

The structure of low density gas phases and crystalline solid states is easy to describe, because the correlation functions for them are easy to obtain. In low density gases, intermolecular interactions are negligible and there are no correlations between the particles. g(r) is 1 for all r. At the other extreme, in crystalline solids correlations are very strong but, due to the lattice symmetry, the structure and correlation functions can be easily determined. Correlation functions are particularly important for dense disordered systems such as liquids and glasses, and hence for polymers, for which the crystalline state is rather the exception than the norm. Different models used in classical liquid state theory are essentially different approximations to calculate the correlation functions. All thermodynamic properties can be expressed in terms of the structure correlation functions and interaction potentials [37,46]. 

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