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Multiscale model of miscible polymer blends in porous media: from flow fields to concentration fluctuations.

We have developed a multiscale approach for simulating the concentration fluctuations in a miscible blend subject to complex flow dynamics. We first simulate the hydrodynamics of a fluid as it flows through porous media. In particular, we monitor the velocity gradients as a function of time for a fluid "particle" as it follows a tortuous path through the system. Next, we evolve the structure factor of the spatial concentration fluctuations subject to this flow environment. The velocity gradients experienced by this fluid particle can result in elongation and rotation of the concentration fluctuations. In this manner, we couple the macroscopic flow fields in porous media with the microscopic concentration fluctuations in the polymer blend. We find a close correlation between the tortuous pathways, the velocity gradients in the fluid, and the perturbance of the structure factor from it quiescent state. Furthermore, we find that the concentrations tend to elongate towards the flow direction or at an acute angle with the flow direction.