Chemical Engineering, Stanford University
"Two Sides of the Evaporation Coin: Stabilizing Foams and Causing Rayleigh-Taylor Instabilities"
Evaporation is a ubiquitous process that is shown to drive important interfacial flow phenomena. In the case of non-aqueous foams, it is demonstrated to cause soluto-capillary Marangoni stresses that can stabilize foams in non-aqueous systems that are free of surfactants and temperature gradients. The mechanism relies on the existence of a distribution of components having different volatilities and, since surface tensions can be directly related to volatility, evaporation leads to surface tension gradients within the top layer of bubbles on a foam, thereby delaying thin film rupture. This finding is verified using the dynamic fluid film interferometer that directly records coalescence times that are used to establish cumulative coalescence time distributions that can be accurately fit to Rayleigh distributions. These results are of direct importance to the design of lubricating oils and other non-aqueous products.
On the other hand, evaporation can induce Rayleigh-Taylor (R-T) instabilities in polymer solutions, which can induce unwanted concentration inhomogeneities. Data are presented that demonstrate this effect for both dextran and PEG solutions and the results are expected to be quite general. We measure the onset time for density stratifications to be created that trigger R-T instabilities. It s shown that a scaling of the onset time with polymer solution viscosity, the R-T wavelength and the evaporation velocity successfully collapses the data collected over a range of polymer concentrations spanning the dilute to semi-dilute regions.
"Lubricin – Alleviating the Effects of Dry Eye"
Dry eye is an affliction where the tear film of the eye is unable to protect the cornea epithelium. One suspected cause of this condition is a deficiency of mucin, a protein that is thought to enhance wettability and reduce friction experienced during blinking. We report on the development of a model for mucin deficient dry eye and an investigation of the ability of lubricin, a heavily glycosylated protein, to restore lubricity and low friction during simulated blink events.
Gerald Fuller is the Fletcher Jones Professor of Chemical Engineering at Stanford University. He joined Stanford in 1980 following his graduate work at Caltech where he acquired his MS and PhD degrees. His undergraduate education was obtained at the University of Calgary, Canada. Professor Fuller's interests lie in studies of rheology and interfacial fluid mechanics. His work has been recognized by receipt of the Bingham Medal of The Society of Rheology, membership in the National Academy of Engineering, election to the American Academy of Arts and Science, and honorary doctorates from the Universities of Crete, Greece, and Leuven, Belgium. He presently serves as the General Secretary to the International Committee on Rheology.