There has been extensive study on the behavior of polymers in the presence of fluid flow over the past century. There remain, however, fundamental questions about how flows couple to molecular degrees of freedom and vice versa. This pressing problem has profound implications in polymer processing in industry, both for traditional polymer systems as well as for advanced applications where the function is intimately tied to processing conditions. We focus on two projects with the general aim of understanding these flow- polymer interactions for systems that are at the forefront of polymer materials. The first project utilizes Brownian Dynamics simulation techniques to examine the behavior of diblock copolymers in equilibrium and flow conditions. In equilibrium the two blocks are found to behave primarily independently, with the end to end distance of the copolymer scaling as expected for two uncorrelated blocks. In flow, however, coupling between the blocks is observed and the stretching behavior of one block is no longer independent of the behavior of the other block. Instead, as one block is stretched it induces stretching of the other block, resulting in stretch transitions happening at an order of magnitude lower flow rates than for the lone block in both shear and planar extensional flows. The second project is a new method for the simulation of semidilute polymers in planar extensional flow that utilizes a consistently averaged method of calculating hydrodynamic interactions that greatly reduces the run time of the simulations. Through the use of the Kraynik-Reinelt boundary conditions, simulation times are not limited by the use of flow. This method allows for the simulation of large systems in extensional flow with reasonable simulation times without requiring supercomputer level hardware.
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Coupling molecular conformation to polymer chemistry and composition via flow
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