Using surfactants to remobilize the interface of a rising bubble a theoretical and experimental study.
Item
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Title
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Using surfactants to remobilize the interface of a rising bubble a theoretical and experimental study.
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Identifier
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AAI3283147
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identifier
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3283147
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Creator
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Taneja, Ashish.
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Contributor
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Adviser: Charles Maldarelli
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Date
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2007
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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
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Abstract
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Generally surfactants retard the terminal velocity and interfacial mobility of rising bubbles. Only remobilizing surfactants do not retard the motion and in this work, we studied the physicochemical regimes in which they do not retard the motion.;In the first regime, we study experimentally surfactants with rapid kinetic exchange which remain in monomeric form at high concentrations. At high bulk concentrations, the adsorption saturates causing the surface concentration distribution to become uniform and the Marangoni retarding force to tend to zero. The remobilizing surfactants chosen are intermediate chain length alcohols. We measure the rise velocity of nitrogen bubbles rising in either water or a 70:30 mixture of glycerol-water, each with dissolved alcohol. For the glycerol/water system rise velocities are reduced relative to bubble motion in water, and the kinetic desorption rate is of the order of or larger than the convective rate. Partial remobilization was observed. In the water system with dissolved alcohols, we find that the large velocities and hence greater convective rates do not permit remobilization due to a kinetic barrier.;In the second regime, we study theoretically remobilization for the case in which the remobilizing surfactant forms micellar aggregates at high concentrations. For bulk concentrations far from the bubble just below the critical concentration for aggregate formation (CMC), a micelle zone appears at the rear end of the bubble due to the elevated surfactant concentrations in the sublayer of liquid next to the bubble. We assume that the exchange of surfactant between micelle and monomer is infinitely fast relative to convective and diffusive rates so that the monomer concentration remains at the CMC. We also assume, as the case for a remobilizing surfactant, that the kinetic exchange is fast relative to surface convection. Hence the sublayer concentration of monomer in the micelle zone is constant, maintaining a uniform surface concentration along the interface adjoining the micelle-zone and is unretarded. As the bulk concentration exceeds the CMC, a micelle free zone appears at the front end of the bubble, and only this part of the surface remains retarded. We obtain numerical hydrodynamic solutions for this micelle-facilitated remobilization for a bubble translating with zero inertia and up to order one rates of diffusion in the bulk relative to convection.
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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.
