The remobilization of the interfaces of moving bubbles and droplets retarded by surfactant adsorption.
Item
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Title
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The remobilization of the interfaces of moving bubbles and droplets retarded by surfactant adsorption.
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Identifier
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AAI9009788
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identifier
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9009788
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Creator
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Stebe, Kathleen Joan.
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Contributor
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Adviser: Charles Maldarelli
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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 | Physics, Fluid and Plasma
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Abstract
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This thesis addresses the influence of surfactant molecules on fluid particle flows in a three part study ((I.), (II.) and (III.)). Surfactant molecules adsorb onto the interfaces of moving fluid particles and are convected to the rear pole of the droplet. Adsorbed surfactant molecules accumulate at this stagnation point if the time scale for interfacial convection is faster than those governing the kinetic exchange of surfactant and bulk diffusion. Surfactant accumulation in this region gives rise to a surface tension gradient along the interface which retards the surface velocity. In this thesis, conditions under which surface velocities of surfactant laden fluid particles can remain unhindered are investigated.;The remobilization of fluid particle interfaces is demonstrated experimentally in (I.) and (II.) using a three phase capillary slug flow in which a train of air and aqueous surfactant solution slugs ride on an annular wetting film of fluorocarbon oil. Surfactant adsorbs along and retards the aqueous-oil interface, significantly increasing the pressure drop required to drive the flow at constant velocity.;In (I.), a fluid particle flow is shown to remain unhindered in the presence of a single adsorbed surfactant. A surfactant with no desorption kinetic barriers, present in concentrations such there are no barriers to diffusive mass transport, adsorbs uniformly along the interface. No gradients in surface tension arise to retard the surface velocity; the flow behaves as it would in the absence of surfactant, save that it has a reduced, uniform surface tension.;The remobilization of fluid particle flows hindered by adsorbed impurities is demonstrated in (II.). A fast adsorbing and desorbing surfactant with no barrier to diffusive transport preferentially adsorbs along the particle interface, preventing the adsorption of an impurity. The remobilizing surfactant establishes a uniform surface concentration (and therefore a uniform surface tension). Thus, competitive adsorption of a fast sorption kinetic surfactant allows fluid particle flows in the presence of impurities to behave hydrodynamically as they would in their absence.;In (III.) a spectrophotometric technique for measuring the oil film thickness around the aqueous slug in the three phase slug flow is described. Initial results indicate that the films are on the order of tens of microns, and decrease with the surface mobility of the oil-aqueous interface. This is attributed to a reduction of the leak rate and the constant rate of oil induction.
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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.
