(119b) Dynamics and Rheology of Bidisperse Polymer Melts through a Simplified Molecular Model

Polydispersity is inevitable in industrially produced polymers as a natural consequence of the polymerization process. Established theories of polymer rheology mostly apply only to monodisperse linear polymers. Dynamics of polydisperse polymers is yet to be fully explored – especially how different chain lengths affect the dynamics of one another in a mixture. In this study, we focused on bidisperse polymers of different compositions as an idealized model system and used a coarse-grained molecular model to explore their dynamics and rheology. Specifically, we considered the effects of longer chains on shorter chains and vice versa in the mean-squared displacement, relaxation spectrum and viscoelasticity. Our simulation results show that longer chains do not have any significant effect on the dynamics of shorter chains regardless of their concentration, while shorter chains serve to speed up the relaxation of longer chains. We further conducted a Rouse Mode Analysis on these systems and found that the relaxation rate of the shorter chains shows a dependence on the concentration of the longer chains, which generally increases with an increased concentration of the latter. Simulation results were also used to evaluate semi-empirical mixing rules proposed in the literature for the prediction of the rheology of polydisperse polymers based on monodisperse rheology and found the results to reasonably predict the rheology of the mixture.