A study of the effects of cohesive forces on the sorption kinetics of surfactants by pendant drop digitization.
Item
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Title
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A study of the effects of cohesive forces on the sorption kinetics of surfactants by pendant drop digitization.
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Identifier
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AAI9130342
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identifier
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9130342
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Creator
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Lin, Shi-Yow.
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Contributor
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Advisers: Charles Maldarelli | Kevin Mckeigue
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Date
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1991
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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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Surfactants are molecules with nonpolar and polar (or ionizable) chemical groups which adsorb preferentially onto a fluid interface where they lower the interfacial tension. When surfactant molecules with single, slender hydrocarbon chains and small polar groups adsorb onto a surface, strong van der Waals attractive forces can develop at sufficiently high surface concentrations. This cohesion arises because at high surface concentrations the adsorbed molecules are pushed out of the surface, and begin to stack lengthwise in loose bundles. This arrangement brings the hydrocarbon chains into close proximity to each other, and strong van der Waals attraction can develop.;The presence of cohesive forces affects the dependence of the equilibrium surface tension and surface concentration on the bulk concentration, and dynamic surface tensions and concentrations caused by nonequilibrium processes involving surfactant bulk-sublayer exchange. In this thesis, these effects are studied theoretically and experimentally. Experimentally, a pendant drop apparatus using video image digitization is developed to measure equilibrium and dynamic interfacial tensions. Theoretically, sorption kinetic models are constructed which incorporate the influence of cohesion through an activation energy approach.;The major results are: (i) cohesive effects give rise to a phase transition like region in which small increases in the bulk concentration cause very large increases in the surface coverage accompanied with little change in the surface tension; (ii) for clean interface adsorption, an early induction period appears in the relaxation in surface tension because of the phase transition characteristic of the equilibrium surface tension; (iii) there are conditions for which the clean interface adsorption is diffusion controlled while the re-equilibration is controlled by both kinetic sorption and bulk diffusion. This leads to the possibility of measuring the diffusion coefficient by comparing measured relaxations for adsorption with the diffusion limited simulations, and then calculating kinetic constants by comparing theoretical and experimental re-equilibrations.
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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.
