Effect of Orientational Coupling Due to Nematic Interaction on Relaxation of Rouse Chains

A polymer chain in a dense and deformed matrix of other chains tends to be oriented in the direction of matrix orientation. This orientational coupling results from an interaction, which we call the nematic interaction in this paper, between the segments of the chain and matrix. To describe the effect of such an interaction on the dynamic behavior of a Rouse chain, we propose a model in which a force leading to the orientational coupling is taken into account. Our model indicates that linear superposability holds for the dynamic response of Rouse chains to small strains imposed, even when the orientational coupling takes place. We have found that the effects of orientational coupling on the viscoelastic and orientation relaxation functions are not necessarily the same. For the linear viscoelastic relaxation, our model suggests no effect of orientational coupling for the Rouse chains in both monodisperse and blend systems. For the orientation relaxation of the Rouse chains in monodisperse systems, we still see no significant effect. On the other hand, for the orientation relaxation of Rouse chains in blends with other chains, our model suggests a significant effect. For this case, the orientation relaxation function of the Rouse chains is written in terms of those of the matrix chains and of the Rouse chains subjected to no nematic interaction. Significant retardation is expected when the Rouse chains are placed in a matrix of much longer chains. This prediction can be tested by optical techniques.