The Rheology of Polymer Solutions in Ultrathin Films via a Combined Finite Elements-Brownian Dynamics Approach

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ABSTRACT Proposal Number: CTS-9731896 Principal Investigator: Shaqfeh This is a grant to address a number of important problems in the study of polymer rheology that can be characterized as non-continuum or non-local. These are typically associated with the influence of boundaries or constrained environments on the stress-strain rate relationship. The burgeoning interest in these problems arises from the growing need to process materials at the molecular level. In most cases, new physical principles need to be applied to such problems because the most fundamental relationships, e.g. the relationship between the tension along a molecular backbone and the average extra stress in the mixture, need to be derived anew. Moreover these highly constrained flow fields are now only beginning to be experimentally interrogated, but the early data suggests that qualitatively new Theological behavior needs to be understood in these cases. Three problems that can serve as paradigms for theoretical model-building have been selected for study: a) the Couette-Poiseuille flow of flexible chains in solution when the pore or channel thickness is comparable to the radius of gyration of the polymers, b) the bulk shearing flow of polymer solutions near a boundary where the interface may contain adsorbed or grafted polymer layers, and c) the squeeze flow lubrication of "wet" polymer brush covered surfaces. The technique will be used is a novel hybrid scheme involving self-consistent flow calculations using HP adaptive finite elements and large scale Brownian dynamics simulations of bead-rod (Kramer's) chains.