Ludwig C. Nitsche
(Ph.D., Massachusetts Institute of Technology, 1989)
Microstructure plays a crucial role in colloidal and macromolecular characterization, fractionation and, processing and in the rheology and dynamics of complex fluids. Research in this area is empowered by three central themes of fundamental research: (i) microstructure and transcendence of scales from the "granular" substructure to a "smooth" continuum description; (ii) Brownian dynamics and/or nonlinear response; (iii) synergistic interactions between different physicochemical phenomena. As the science and industry of engineered microstructures and microrheology pushes the scale of pore transport and membrane fractionation down to molecular dimensions, a new conceptual frontier opens in harnessing complex fluids and the dynamics of macrosolutes in systems where the bounding porous geometry is not much larger than the fluid substructure. Major technological challenges in biochemical engineering and waste treatment reside precisely where continuum mechanics and the traditional paradigm of widely separated scales lose their power.
My research program emphasizes theoretical analysis of concrete micromechanical models in order to elucidate subcontinuum dynamics and to extract macroscopic transport behavior from the underlying microphysics. The approach involves hybridizing analytical or asymptotic methods with large-scale computation, and the development or refinement of special numerical techniques for modeling flow in complex pore-scale geometries. Additionally, experiments are being started on a new approach to membrane separations, using well-characterized membrane-macrosolute systems.
Our efforts are directed in three main areas:
- Asymptotic and computational design modeling combined with experimental testing of antipolarization dialysis ("APD") --- a new technology for fractionating colloidal particles and macromolecules that,operates by modulating ultrafiltration with dialysis in a special high-aspect-ratio flow geometry. Initial stages of research will emphasize the resolution of protein mixtures.
- Nonlinear inertial drift phenomena applied to pore diffusion of colloidal particles. Net motion can be induced by zero-mean oscillations, for which the ultimate application is a novel acoustic "diffusion gate" technology for influencing hindered membrane transport.
- Interaction of hydrodynamics, Brownian motion, colloidal forces and conformational dynamics in determining the migration behavior of polymers in complex microporous media. This forms the micromechanical basis for Theological constitutive equations on the observable scale.
SELECTED RECENT PUBLICATIONS
With Hinch EJ. Shear-induced lateral migration of Brownian rigid rods in parabolic channel flow. J. Fluid Mech., 332: 1-21 (1997).
Fluctuation-flipping orbits of freely-draining dumbbells in converging-diverging pore flows. Chem. Eng. Commun.,148--150: 593--621 (1996). [Invited contribution to special Festscrift volume honoring Professor Howard Brenner on the occasion of his 65th birthday.]
One-dimensional stretching functions for Cn patched grids, and associated truncation errors in finite-difference calculations. Commun. Numer. Methods. Eng.,12: 303--316 (1996).
Cross-stream migration of bead-spring polymers in nonrectilinear pore flows. AICHE Journal,42: 613--622 (1996).
A singular perturbation analysis of antipolarization dialysis at high aspect ratio. Indust. Eng. Chem. Research, 34: 3590--3605 (1995). [Invited contribution to special issue honoring 35 years of the textbook Transport Phenomena by R. B. Bird, W. E. Stewart and E. N. Lightfoot.]
With Zhuge S. Hydrodynamics and selectivity of antipolarization dialysis. Chem. Eng. Sci., 50: 2731--2746 (1995).
Pseudo-Sedimentation Dialysis: An Elliptic Transmission Problem. Quart. Appl. Math., 52: 83--102 (1994).
With E. J. Hinch. "Nonlinear Drift Interactions Between Fluctuating Colloidal Particles: Oscillatory and Stochastic Motions." J. Fluid Mech., 256: 343--401 (1993).
"A New Lift for Centrifugal Impellers?" Chem. Eng. Progress, 87: 73--79 (1991).
With H. Brenner. "Hydrodynamics of Particulate Motion in Sinusoidal Pores via a Singularity Method." AICHE J.,36: 1403--1419 (1990).
With H. Brenner. "Eulerian Kinematics of Flow Through Spatially Periodic Models of Porous Media." Arch. Rational Mech. Anal., 107: 225--292 (1989).
With J. M. Nitsche and H. Brenner. "Existence, Uniqueness and Regularity of a Time-Periodic Probability Density Distribution Arising in a Sedimentation-Diffusion Problem. SIAM J. Math. Anal.,19: 153--166 (1988).