Hello Cruel World
Tuesday, August 03, 2004
Self-organizing systems & cornstarch in water
Robert D. Deegan
Research Associate, Center for Nonlinear Dynamics & Department of Physics
University of Texas at Austin
Corn starch movie (4 Mb Windows Media file)
Research: Simple systems driven from equilibrium will spontaneously form patterns. For example, a thin layer of liquid heated from below develops hexagonally ordered convection cells. The Earth is a system driven by the constant flux of energy from the sun and geothermal processes, and we see around us an enormous variety of organized structures: hurricanes, the earth’s magnetic poling, and the Devil's post pile. Are these structures like the patterns of simple systems: an inevitable product of the forcing? Is life itself a generic manifestation of driven systems? These are fascinating issues that research on nonequilibrium systems and pattern formation will hopefully one day answer.
My research focus is patterns in fluids and solids. I discovered that vibrated shear thickening fluids--fluids that become more viscous as the shear rate increases, e.g. cornstarch in water--can support holes and can develop large finger-like protrusions, and I'm now trying to understand these structures. Recently, I designed and built an apparatus to fracture single-crystal silicon at 77o K in order to test the theoretically predicted velocity gap, a range of velocities in which crack propagation cannot occur in the absence of thermal fluctuations. I also examined two different fracture instabilities: wavy cracks in thermally quenched silicon, and the oscillating path of a crack in rubber, such as when a balloon is popped.
As a graduate student in Professor Sidney Nagel's lab, I studied the glass transition and patterns formed by the precipitation of solute from a drying drop. The starting point for latter project was the observation that coffee stains are always ring shaped, i.e. darkest along the perimeter.
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