Dynamics of polymer adsorption from dilute solution in shear flow near a planar wall.

Adsorption of polymers from dilute solution subject to shear flow near a planar wall is studied using kinetic theory. A dumbbell model consisting of two beads connected by a nonlinear spring is used to describe the polymer molecules, and the beads interact with the wall via a short-range exponential potential. Bead-bead and bead-wall hydrodynamic interactions are also included in the theory. For an initially bare surface, it is found that the quantity of polymer adsorbed decreases with an increase in polymer molecular weight at a given shear rate and point in time. In addition, for a given molecular weight and point in time, the quantity adsorbed decreases with an increase in shear rate. When adsorbed polymer is initially present, similar trends are observed. Furthermore, complete desorption can be achieved at a sufficiently high shear rate. In all cases, the time required to approach a steady value of the adsorbed amount is many orders of magnitude larger than the dumbbell relaxation time. The above findings are in qualitative agreement with experimental measurements reported nearly three decades ago by Lee and Fuller [J. Colloid Interface Sci. 103, 569 (1985)]. Our findings also suggest that the physical mechanism underlying the long-standing observation that shear flow inhibits polymer adsorption and assists polymer desorption is hydrodynamic interaction between stretched polymer molecules and the adsorbing surface.