Rheology of Complex Fluids. Many everyday substances are not readily classified as solids or liquids, but have flow properties somewhere in between. Examples include mayonnaise, toothpaste, and silly putty. Such fluids typically have a polymeric or colloidal microstructure much larger than the atomic which dominates the rheological (i.e., flow) properties. Through rheological experiments, theory, and computer simulations, I am trying to work out the relationship between the structure of complex fluids and their rheology. Such knowledge is valuable in the optimal design of such fluids for applications in the polymer, pharmaceutical, and electronics industries. Of particular interest at present are branched polymer melts, surfactant solutions, and biopolymers. For a movie showing the measurement of the extensional rheology of polymer melts, click here.

Flow Properties of Biomolecules. An area of rapidly growing interest is the micromanipulation of biomolecules such as DNA, for genome analysis and other applications. Using theories of polymer flow dynamics adapted to DNA molecules, combined with microscopy experiments, we are attempting to facilitate the use of flow fields for manipulating DNA and other biomolecules. For a video showing experimental and simulated imagespolymer/ of a DNA molecule stretching in an extensional flow, go to the DNA page.

Simulation of Surfactant and Lipid Microstructures. Because of increases in computer speed, lattice simulation methods such as Monte Carlo sampling can now be used to predict the structure and self assembly of complex microstructures including micelles, liquid crystalline phases and their phase diagrams. My group is developing fast lattice methods that can be used to determine the relationship between molecular architecture and the self-assembled structure. Recent work concentrates on polymer/surfactant complexes, including micellization along polymer chains. We have determined the structures of micelles formed from mixed surfactants, including the formation of rod-like micelles and a very unusual donut-shaped micelle. We are also using molecular dynamics methods to simulate lipid/protein interactions, including the proteins in lipid membranes. We are especially interested in the structure of lung surfactant, which contains not only surfactants, but proteins which are responsible for the ability of lung surfactant to expand and compress without collapse. The absence of the protein SP-B in the lungs of pre-mature infants is believed to be responsible for respiratory distress syndrome, the most serious life-threatening condition common in infants of fewer than 26 weeks gestation. Our molecular dynamics simulations are attempting to determing the location and orientation of the SP-B protein in a monolayer of lung surfactant.

Viral Genomics Using Microfrabricated Devices (with Burns, Solomon, Burke and Fuller) We are developing microfabricated devices capable of distinguishing variations in viruses by detecting differences in their genomes. Such devices would allow cheap, portable, rapid diagnosis of variations in rapidly mutating viruses, such as influenza.

Graduate Students:

Bruce Schiamberg (PhD candidate)
Anshuman Roy (PhD candidate)
Lin Fang (PhD candidate)
Zheng Chen (PhD candidate, with Mark Burns)
Sean Holleran (PhD candidate)
Youngsuk Heo (PhD candidate)
Weixian Shi (PhD candidate)
Ji Hoon Kim (PhD candidate)
Tyson Poeckh (PhD candidate, with Mike Solomon)
Hwan-hyu Lee (PhD candidate)
Qiang Zhou (PhD candidate)
Semant Jain (PhD candidate)
Laura Shereda (PhD candidate, with Mike Solomon)
Susan Weitz (PhD candidate)

Post-docs: