Hindered Diffusion in Polymer Gels:

Our theoretical work in hindered transport is focused on developing mathematical theories for calculating the hydrodynamic and electrostatic interactions that affect diffusion and convection in suspensions and polymer systems. Ultimately, a detailed theoretical understanding of hindered transport will allow one to tailor membrane or gel properties, such as fiber volume fraction and surface charge density, to separate a particular mixture. Our theoretical work is complemented by experiments in which we measure rates of hindered diffusion of proteins and micelles in polymer solutions and gels. Our work with micelles is done in collaboration with Professor Stephanie Dungan, who studies the behavior of micelles, emulsions and microemulsions in complex environments. We perform these measurements by using holographic laser interferometry, which is a method for monitoring diffusion by observing interference fringes formed from laser light. It is a direct, non-invasive procedure that requires minimal assumptions to interpret the data.

Mechanics of Non-Newtonian Suspensions:

Even in Newtonian fluids, the complex nature of many-particle, hydrodynamic interactions has made the theoretical calculation of suspension properties such as viscosity and sedimentation rate a difficult, although no longer impossible, task. We are currently working on the related, but far more complex, problem of the behavior of suspensions of particles in non-Newtonian polymer solutions. Even with two or three particles, the non-Newtonian nature of the fluid causes dramatic changes in behavior that are still not understood. We have developed a new technique for simulating the motion of N particles in viscoelastic polymer solutions. The method is based on the idea that a suspension of bead-and-spring dumbbells contains many of the properties of a polymer solution. Hence, particles moving in and interacting hydrodynamically with a medium of thousands of such dumbbells exhibit much of the qualitative behavior found experimentally in real suspensions. We are also performing experiments in which we observe the sedimentation of both small groups of particles and full suspensions. The motion of small groups of particles is videotaped for comparison with our simulations (see, for example, the "Six-Sphere Inverting Star"), while the microstructure and sedimentation velocity of the suspensions are monitored by using nuclear magnetic resonance (NMR) imaging. The instruments for the NMR experiments are made available through the UC Davis NMR center, and some typical images are attached. More information on the simulations, including some short animations, can be found on the homepage of Dr. Housam Binous, who recently completed his Ph.D. in my research group. More information on research in suspension mechanics at UC Davis, particularly with regard to the use of NMR imaging, can be found on the homepage of Professor R. Powell. The web site for the course ECH 150C, Rheology and Polymer Processing, may also be of interest.

Nolan, S.L., Phillips, R.J., Cotts, P.M. and Dungan, S.R., "Light Scattering Study on the Effect of Polymer Composition on the Structural Properties of PEO-PPO-PEO Micelles," J. Colloid Interface Sci. 191:291 (1997).

Clague, D.S. and Phillips, R.J., "A Numerical Calculation of the Hydraulic Permeability of Three-Dimensional Disordered Fibrous Media," Phys. Fluids 9:1562 (1997).

Chun, Myung-Suk and Phillips, R.J., "Electrostatic Partitioning in Slit-Pores by Gibbs Ensemble Monte Carlo Simulation," AIChE J. 43:1194 (1997).

Kong, D.D., Dungan, S.R., Kosar, T.F. and Phillips, R.J., "Measurement of Hindered Diffusion of Proteins and Micelles in Agarose Gels by Holographic Interferometry," AIChE J. 43:25 (1997).

Clague, D.S. and Phillips, R.J., "Hindered Diffusion of Spherical Macromolecules through Dilute Fibrous Media," Phys. Fluids 8:1720 (1996).

Phillips, R.J., "Dynamic Simulation of Hydrodynamically Interacting Spheres in a Quiescent Second-Order Fluid," J. Fluid Mech. 315:345 (1996).

Phillips, R.J., "Calculation of Multisphere Linearized Poisson-Boltzmann Interactions near Cylindrical Fibers and Planar Surfaces," J. Colloid Interface Sci. 175:386 (1995).

Chui, M.M., Phillips, R.J. and McCarthy, M.J., "Measurement of the Porous Microstructure of Hydrogels by Nuclear Magnetic Resonance," J. Colloid Interface Sci. 174:336 (1995).

Corbett, A.M., Phillips, R.J. and McCarthy, K.L., "Magnetic Resonance Imaging of Concentration and Velocity Profiles of Pure fluids and Solid Suspensions in Rotating Geometries" J. Rheology 39:907 (1995).

Kosar, T.F. and Phillips, R.J., "Measurement of Hindered Diffusion by Holographic Interferometry," AIChE J. 41:701 (1995).