DMR-Dynamics of Branch Point Motion in Entangled Polymers

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Under this grant, the slip-link algorithm will be extended to the case of polymers with multiple branch points, for which a theory for branch-point motion is required. As a test case, a series of asymmetric stars will be considered, ranging from one with a zero-length third arm (which is therefore a linear polymer) to one whose third arm has length equal to the other two (a symmetric star). The experimental relaxation behavior for this series of polymers will be predicted, including the hitherto unexpected finding that even a small third arm with only two or three entanglements slows down the dynamics of the star much more than predicted by existing dynamic dilution theories, making a short arm nearly as effective as a much longer arm in slowing down the relaxation. This success of the slip-link model implies that the algorithm has the potential to capture accurately the physics of branch-point motion, which is a necessary requirement for understanding the dynamics of more complex H and comb polymers, as well as mixtures of these with linear polymers and with each other. The slip link algorithm will thus be extended to the cases of H and comb molecules and the effect of branch point dynamics on their relaxation properties will be explored, comparing the predictions of the model with recently obtained experimental data. We will also explore branch-point motion with a more sophisticated real-space slip-link model that has been recently developed by colleagues at Nagoya University. The goal is to obtain an accurate theory of branch-point motion, which is the most important missing ingredient required for development of general theories of polymer melt relaxation. The results obtained from these simulations will be incorporated into a general hierarchical model for relaxation of general polydisperse branched polymer melts, thus enhancing our ability to use rheological theory to infer molecular branching structure from rheological data, which is an important practical and commercially valuable goal. The research will continue international collaborations with the group of Masao Doi at Nagoya University in Japan. %%%This theoretical research project will extend the PI's successful models to other polymer structures. The models will then be able to better describe polymer melt relaxation and subsequently the flow of polymers. Conversely, using this theory, relaxation measurements will yield information about molecular branching structure of polymers. The work will be done in collaboration with a group at Nagoya University, Japan.***