"The Effects of Finite Concentration and Surfactants on the Coalescence of Drops in Flow"

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ABSTRACTPROPOSAL NO.: CTS-0624446PRINCIPAL INVESTIGATOR: GARY L. LEALINSTITUTION: UNIVERSITY OF CAL- SANTA BARBARAThe Effects of Finite Concentration and Surfactants on the Coalescence of Drops in FlowThis grant will facilitate a study of the process of flow-induced coalescence of drops in a miniature version of the 4-roll mill, that allows control of the position and orientation of a pair of drops (down to the 5-10 micron range) while they are colliding in a flow. This device allows unique experiments that can be used to explore the coalescence process at the level of the individual drops, and this has led to a number of unexpected results, which demonstrate significant flaws in current scaling type theories that are used for the prediction of drop size distribution in mixing and blending devices. This study was originally motivated by the need for a better understanding of the process of blending or emulsification processes for viscous fluids in the presence of a surfactant. The present studies consider two important extensions of previous work: (1) one is to consider the coalescence of drops at non-dilute concentrations where interactions with other surrounding drops are expected to play an important role; (2) the second is to extend current theoretical calculations to include surfactant effects, and thus seek to understand recently obtained data for this problem. Comparisons between theoretical simulations of surfactant effects and experiments will not only help to better understand the role played by surfactant, but will also provide a test of the applicability of the small molecule model for copolymer surfactants. The expected practical significance of this work is ultimately a better basis for predicting the outcome of a blending process, and how it will be modified by changes in the bulk and interface properties, the relative quantities of the two bulk fluids, and particularly how to optimize the process in terms of the controllable parameters of the compatibilizer. The theoretical aspects of this project will be carried out with the collaboration of the "complex fluids" group of the IGERT program at UCSB on scientific computing. The PI will also utilize the nationally well-known outreach program of the MSERC at UCSB to engage at least one undergraduate student each summer, to be involved in experimental studies that are proposed. In general terms, effective models for blending or emulsification in viscous fluids will play a major role in understanding, optimizing and developing new multi-component polymeric materials.