Lubrication by Confined Polymers
Michael Rubinstein (University of North Carolina), Aykut Erbas (University of North Carolina), Ekaterina Zhulina (University of North Carolina)
Complex Fluids: Suspensions, Emulsions, and Gels
Wed 9:00 - 10:30
Barus-Holley 160
Polymers play a major role in lowering friction in numerous man-made devices and in many major parts of our body including joints, such as knees and hips, and beating cilia in lungs. Polymers in most of these cases are confined in small gaps between two moving solid surfaces. Thus there is a need for quantitative molecular models of dynamics of polymers confined to spaces comparable or smaller than polymer dimensions. It is not even clear what parameter properly describes these situations – friction coefficients or effective viscosities. Using Rouse model of unentangled polymer solutions and melts we argue that effective viscosity is the proper parameter describing lubrication by confined polymers. We develop a scaling model relating the shear forces between two compressed neutral polymer and polyelectrolyte brushes in both linear and non-linear regime to number of monomers per chain, grafting density of chains, separation between plates, and charge density for polyelectrolyte brushes. The predictions of the model are in good agreement with results of molecular dynamics simulations.