Non-monotonic hydrodynamic lift force on highly extended polymers near surfaces

Abstract

The hydrodynamic lift force that polymers experience near boundaries is known to be a crucial element when considering rheological flows of dilute polymer solutions. Here we develop a theory to describe the hydrodynamic lift force on extended polymers flowing near flat surfaces. The lift force is shown to display a non-monotonic character increasing linearly with the distance to the wall Z in the near-surface regime defined as Z < L, with L being the contour length of the polymer. At heights Z ∼ L the lift force displays a maximum, and for Z > L we recover the well-known far-field result in which the force decays as Z−2. Our analytical theory has important implications in understanding adsorption, desorption, and depletion layers of highly extended objects in flow.