Professor
Department of Food Science and Technology
Department of Chemical Engineering and Materials Science

110 FST Bldg   
srdungan@ucdavis.edu
(530) 752-5447 office

Education

B.S.E., 1984, Princeton University
S.M., 1988, Massachusetts Institute of Technology
Ph.D., 1991, Massachusetts Institute of Technology

Research Interests

Our group is investigating transport into and out of micelles, particularly as it occurs within complex systems such as emulsions and gels. Surfactant aggregates known as micelles have a profound effect on the rate at which oils and other hydrophobic solutes are transported out of oil droplets within emulsions, and this transport has a major impact in such areas as food stability, flavor perception, and oil metabolism within humans. Yet little is known about how such solutes cross the oil/water interface to move into or out of micelles. We seek to understand these interfacial transport processes through a combination of experimental measurements of oil solubilization kinetics with fundamental models of interfacial dynamics during solute transport. Experimental tools include light scattering, differential scanning calorimetry, and nuclear magnetic resonance, and our theoretical approach employs boundary integral numerics to model the interfacial transport processes. An exciting application of this area of research is our effort to use an understanding of interfacial kinetics to improve upon a new technology for using micelles to extract cholesterol from milk fat.

In a second area of research, we are examining the impact of micellar aggregates on the solubility and transport of hydrophobic solutes within a novel gel material that contains entrapped micellar micro-domains. Experiments in our laboratory have shown that solutions of large block copolymer aggregates are effectively immobilized within an alginate gel matrix, and this gel can be used to extract a model hydrophobic solute, such as naphthalene or pyrene, from an aqueous solution. This ability to extract and concentrate hydrophobic substances from water has important implications for wastewater treatment applications, as well as for controlled release of drugs, pesticides, or flavors.

It is currently unknown how the micelle-forming, solubilization and transport properties of surfactant molecules are affected by a surrounding gel matrix. Understanding the effect of a fibrous matrix on micelles is important not only for this new micelle/gel material, but also for micelle transport through membranes and for amphiphilic drug transport within human membranes. A particular focus of our work is thus to determine how the capacity of the micelle/gel material to solubilize hydrophobic solutes is influenced by surfactant-gel fiber interactions. As in the emulsion systems, these interactions include electrostatic and hydrophobic forces between the surfactant and gel polymer molecules, coupled with steric interactions arising from the constrained nature of the gel matrix. The effects of micelle-gel association are examined experimentally by measuring naphthalene partitioning into the micelle/gel material, by using dye and fluorescent probe techniques to investigate the micelle structure, and by using a method known as holographic interferometry to measure micelle transport (see homepage of R.J. Phillips). For complex solutions such as the micelle-gel polymer system we consider here, theoretical models based on self-consistent mean field theories are also employed to provide insights into the nature of changes in surfactant structure and stability.

In addition to our work with micelles, we are exploring the use of water-in-oil microemulsion phases for extracting proteins from an aqueous solution. Water-in-microemulsions (also called "reversed micelles") are nanometer-sized droplets of water which form spontaneously in oil in the presence of certain surfactants. One goal is to develop a more effective approach than is currently available for the purification of whey protein mixtures, which are a by-product of cheese manufacture. Equilibrium partitioning experiments allow us to determine the relative affinity of the different components of whey proteins for the reversed micellar phase, and to explore how differences in protein size and hydrophobicity, as well as protein charge, affect their solubilization within the microemulsion. One interesting outcome of this research was the discovery that the smaller of the two milk proteins, a-lactalbumin, has a substantial effect on the properties of the microemulsion phase, suggesting that this small, interfacially active protein may act as a "cosurfactant" and aid in the formation of the microemulsion phase. This observation gives rise to the possibility of using proteins such as a-lactalbumin to aid in the formation of biocompatible microemulsions.

Support

• California Dairy Research Foundation
• National Science Foundation
• United States Department of Agriculture
• Dairy Management, Inc.
• Procter and Gamble