We present a modification of the generalized Flory dimer theory toinvestigate the nematic (N) to isotropic (I) phase transition in chain fluids.We focus on rigid linear fused hard-sphere (LFHS) chain molecules in thisstudy. A generalized density functional theory is developed, which involves anangular weighting of the dimer reference fluid as suggested by decouplingtheory, to accommodate nematic ordering in the system. A key ingredient of thistheory is the calculation of the exact excluded volume for a pair of moleculesin an arbitrary relative orientation, which extends the recent work byWilliamson and Jackson for linear tangent hard-sphere chain molecules to thecase of linear fused hard-sphere chains with arbitrary intramolecularbondlength. The present results for the N-I transition are compared withprevious theories and with computer simulations. In comparison with previousstudies, the results show much better agreement with simulations for both thecoexistence densities and the nematic order parameter at the transition.
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