9307890 Radke The PI has pioneered a novel growing-drop technique for studying rates of adsorption at fluid/fluid interfaces. The proposed growing-drop method relates the instantaneous pressure and size of a radically expanding liquid drop to the dynamic interfacial tension arising from sorption of surface-active solutes. Preliminary measurements with surfactant-free surfaces obtain accurate tension values over a wide range of tensions and times and for both liquid/gas and liquid/liquid interfaces. Initial modeling establishes that transport of a prototype nonionic surfactant, 1-decanol, to a radically growing aqueous/air surfaces is diffusion limited. This powerful growing-up technique is applied to study interfacial sorption rates and mechanisms. Ionic surfactants, micellar solutions, and surfactant mixtures will be studied, and theories describing their transport will be developed and tested experimentally. Adsorption rates of synthetic and natural macromolecules will be measured. Studies of nonionic ethylene oxide surfactants ranging from two to thousands of ethylene oxide groups will be undertaken with the goal of defining the limit at which molecular reorientation at the interface causes a change from diffusion to kinetic controlled adsorption. Likewise, adsorption kinetics of proteins will be investigated in an attempt to determine the conditions and time scale over which proteins retain their native configurations at interfaces.. Finally, the growing-drop apparatus will be modified to incorporate oscillating drops, this opening new vistas for understanding desorption kinetics. Transport of surface-active substances to and across liquid/gas and liquid/liquid interfaces is a determining factor in foam and emulsion stability, in bubble and droplet motion during two- phase separation processes, and in multiphase and dispersed phase flow in porous media. In enzyme catalyzed bioreactors, rates of enzyme adsorption at interfaces are a significant factor limiting maximum reactor residence times. In biopharmaceutical packaging of proteins competitive rates of adsorption between proteins and surfactants can determine the chemical stability of the protein during shipping. At a fundamental level, kinetic rates of adsorption reflect molecular configuration and orientation at interfaces. Dynamic interfacial tension is a convenient probe for revealing surfactant adsorption/desorption kinetics at deformable interfaces. Upon disturbing the interface, the interfacial tension is monitored as a function of time to expose surfactant accumulation.
