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Fluid Dynamics Seminar

Monday, March 9, 2009, 4:00 PM
Cullimore Lecture Hall, Room 611
New Jersey Institute of Technology

Hydrodynamic Interactions between Colloids in Nonadsorbing Polymer Solutions

Tai-Hsi Fan

Department of Mechanical Engineering, University of Connecticut

Abstract

Understanding hydrodynamic interactions of colloids in colloid-polymer mixtures is important for many chemical processes in food, cosmetic, environmental, and pharmaceutical industries. Among various crowding effects in colloid-polymer mixtures, polymer depletion is well recognized as one of the primary mechanisms affecting the dynamics and stability of colloid dispersions. In nonadsorbing polymer solutions, polymer chains tend to be away from the colloid surface and form a depletion zone to avoid the loss of configurational entropy. This polymer depletion zone complicates colloid's transport behavior and causes flocculation due to the unbalanced entropy force. The thermodynamic origin of such depletion-induced flocculation is well understood, but the relevant hydrodynamic interactions are not yet resolved. In this talk, a continuum approach will be presented for solving the hydrodynamic interactions of two spheres with relative motion along the symmetric axis. A numerical m! odel based on the classical vorticity-streamfunction method is used to solve the modified Stokes equation with nonuniform viscosity, which connects to the background polymer distribution established by the equilibrium mean-field approximation. The resulting mobility function is essential in predicting the of diffusion-limited aggregation kinetics.