Ph.D. Student Mark Wilson Heads North for Conference

Ph.D. Student Mark Wilson heads up to Ventura, CA for the annual Gordon Research Seminar and Conference to present his research titled: “STRUCTURE AND RHEOLOGICAL PROPERTIES OF SELF-ASSOCIATING POLYMER NETWORKS.”

Mark Wilson is with the Computational Science Research Center (CSRC) department.  He works with Professor Dr. Arlette Baljon here in the physics department on Polymer Physics.  See below for his abstract.



Systems of associating polymers possess the ability to span a large spectrum of material properties, from fluid-like viscosity to near solid-like elastic dynamics. Relatively small changes in external parameters can result in large transitions in this behavior. In the following, numerical simulations of associating polymers are utilized to study viscoelastic behavior. A hybrid Molecular Dynamics, Monte Carlo (MC) algorithm is employed. Polymer chains are modeled as a course grained bead-spring system. Functionalized end groups, at both ends of the polymer chains, can form reversible bonds according to MC rules. At high temperatures the system is shown to behave as a fluid. Decreasing the temperature below the micelle transition results in a self-assembly of the system, forming a network that is transient in time. The nodes of this network consist of aggregates of end groups, while links between aggregates are formed by one or more bridging polymer chains. We report on the macrostructural changes in a polymer network that arise in response to an oscillatory shear. The stress response has been obtained as a function of the oscillatory frequency and amplitude in both the linear and nonlinear regimes. Data are correlated with observed changes in the network structure. For instance, a reduction in the number of links is observed at large amplitude or low frequency. This is partly due to an increase in the number of loops (chains that have both ends connected to the same aggregate). The secondary cause is a tendency of the chains to form additional bridges between the same sets of aggregates. We have also studied the lifetime of aggregates and found that the lifetime is shortest near the walls that bound the system. Finally, we will report on very intriguing transient phenomena in the moduli, as well as the structure and dynamics of the networks.



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