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

Department of Materials Science and Engineering, Massachusetts Institute of Technology 77 Mass. Ave. Cambridge MA 02139, USA

^a cesing@mit.edu

Received: 25 April 2011
Accepted: 26 June 2011

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.