Phase separation kinetics of liquid crystalline polymers: Effect of orientational order

Phase separation kinetics of main-chain liquid crystalline polymers (LCP's) is investigated by numerically solving time-dependent Ginzburg-Landau equations for the compositional order parameter phi and the orientational order parameter S-ij. The kinetic coefficients are evaluated by using the biased reptation model with a microscopic model of wormlike chains. In numerical simulations we find the formation of a percolated network structure rich in LCP's that resembles that observed in experiments. In our kinetic equations the coupling between compositional order and orientational order appears in (i) the presence of the off-diagonal kinetic coefficient Lambda(phi S) and (ii) the dependence of the kinetic coefficients on S-ij (LCP's tend to diffuse parallel to the nematic orientation). We show by a linear analysis of the growing modes that the presence of Lambda(phi S) suppresses the growth of the compositional order in the early stage. We also show that the tendency of LCPs to diffuse parallel to the nematic orientation is responsible for the breakage of the network structure. [S1063-651X(99)14303-4].