Molecularly Non-Homogeneous Nematic Polymers
Most main chain liquid crystalline polymers are synthesized with the mesogenic groups (rods) linked by flexible spacers, such as repeated methylene groups. The theories presented so far deal either with rigid rods system (Flory1 and Onsager2), or model semiflexible polymer liquid crystals by either the freely-jointed rod chain, or by the worm-like chain36. The rigid rod model does not allow any flexibility of polymer chain. However when the chain is not completely rigid, chain flexibility in fact has significant effect on the properties of polymers. The freely-jointed rod chain treats the polymer as repeated rods, but it fails to deduce the transition to rod behaviour expected when nematic field is strong. On the other hand, the worm-like chain theory has been successful and gives better agreement with experiments. More recently Yurasova and Semenov7 presented a model which attacks the non-homogeneous chain mentioned above. But they relax the concept that chain tangent vector is a unit vector, so that the problem can be analysed in terms of the standard Wiener integral which is solvable mathematically. It is well known that the relaxation of this constraint can fail to give correct results even when dealing with the simple case, e.g. the long isotropic chain8.
KeywordsNematic Phase Persistence Length Liquid Crystalline Polymer Liquid Crystal Polymer Mesogenic Group
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