Hongbo Ma, Chemical and Biological Engineering, University of Wisconsin at Madison, 1415 Enginnering Dr., Madison, WI 53706, Juan J. De Pablo, Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison, WI 53706-1691, and Michael D. Graham, Chemical and Biological Engineering, University of Wisconsin-Madison, 1415 Engineering Dr., Madison, WI 53706.
We study the retention problem in polymer solution flows in a porous media. As a simplified system, a bead-spring chain model of a dissolved polymer molecule confined between two solid walls with a cavity on one of them is considered. The solvent flow field is computed using the Lattice Boltzmann method, and each bead of the polymer chain is treated as a stokeslet. It is observed that the concentration inside the cavity is larger than that in the bulk flow. Previous theories argue that this concentration difference is because of the free energy difference due to the less stretch of the polymer molecule in the cavity. However, a recent kinetic theory identifies another migration mechanism based on the modification of the hydrodynamic interactions between the polymer molecule segments by the slit wall. Our simulation addresses this issue. The stretch of polymer molecule and normal stress of the flow inside and outside the cavity are obtained from the simulation. The hydrodynamic interactions are artificially turned on and off to reveal their importance. The final conclusion clarifies the origin of the retention of polymer molecules in porous media.