The influence of surfactants on the motion of spherical fluid particles in an infinite medium and in a tube.
Item
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Title
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The influence of surfactants on the motion of spherical fluid particles in an infinite medium and in a tube.
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Identifier
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AAI9009739
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identifier
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9009739
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Creator
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He, Zunqing.
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Contributor
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Advisers: Charles Maldarelli | Zeev Dagan
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Date
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1989
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Language
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English
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Publisher
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City University of New York.
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Subject
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Engineering, Chemical | Engineering, Mechanical
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Abstract
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This thesis studies the influence of surfactant adsorption on the hydrodynamic creeping motion of fluid spheres. Bulk soluble surfactant molecules, present in the continuous phase through which fluid droplets translate, adsorb onto the droplet surface and are convected towards the trailing stagnation pole of the surface. Accumulation at this pole lowers the interfacial tension and creates a Marangoni tension directed towards the leading pole. As this tension opposes the surface flow, the flow is retarded. This retardation is the origin of the surfactant effect on the hydrodynamic motion.;Four problems concerning this physicochemical effect are considered. The first two problems consider the axisymmetric translation of a droplet in an infinite medium. The first one examines the steady motion when the surfactant sorption kinetics is slow in comparison to interfacial convection, and a stagnant cap forms at the trailing stagnation point. A solution for the cap angle, as a function of the physicochemical parameters, has been obtained based on a nonlinear surface equation of state, the Frumkin equation, which accounts accurately for the compression of surfactant in the cap.;The second problem studies the unsteady translation of a droplet in an infinite medium due to the transient adsorption of surfactant. Solutions are presented for the unsteady motion for the cases in which the adsorption time is much larger than the characteristic convection time (small Biot number) and when the two time scales are comparable.;The other two problems are concerned with the steady, axisymmetric motion of a spherical drop in a tube. The first problem addresses the case in which the adsorption kinetics is fast relative to surface convection. A first order correction to the Hadamard-Rybczynsky terminal velocity is obtained, which accounts for the influence of surfactants on the droplet motion. The major conclusion of this study is that when a droplet is suspended in Poiseuille flow, the presence of stagnation rings on the droplet surface gives rise to surfactant distributions which can increase the droplet velocity in comparison to that of an uncontaminated droplet.;The fourth problem examines the case in which the sorption kinetics is slow relative to convection, and a stagnant cap forms. Solutions for the terminal velocity of a drop with a cap are calculated as a function of the surfactant physicochemical parameters using the nonlinear Frumkin equation.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
