On the Isotropic-Nematic Transition in Polymer Liquid Crystals

A system of polymers dissolved in liquid crystal is studied in the isotropic phase. A mean eld theory is proposed which undergoes spontaneous breaking of the rotational symmetry and reduces to the theory of polymer nematics. In order to eliminate closed loops of polymers from entering into the theory, the polymers are replicated n times and then n is taken to zero similarly to the procedures of de Gennes and Des Cloizeaux. The transition is rst order, and the presence of the polymers shifts the critical point down, in agreement with physical expectations. The eeect of polymer-polymer interactions is discussed.