Interbubble gas diffusion and the stability of foams.
Item
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Title
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Interbubble gas diffusion and the stability of foams.
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Identifier
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AAI9830709
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identifier
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9830709
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Creator
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Gandolfo, Francois Gerard.
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Contributor
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Adviser: Henri Louis Rosano
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Date
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1997
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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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Chemistry, Physical
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Abstract
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Powders consisting of solid microspheres, produced by spray-drying a feed composed of a surfactant and a shell-forming substance, have many applications in the medical and food industries, one of the most familiar being foaming coffee-creamer powders. These are typically dissolved in an aqueous solution (coffee at near boiling temperatures) and produce a foam in addition to adding a creamlike flavor. The present study discusses (i) the role played by the physico-chemical properties of the feed, and by the spray-drying process itself, in determining the characteristics of the powder; (ii) factors affecting the foamability, i.e., the ability to form a liquid film, of various aqueous solutions; and (iii) the stability and decay of the resulting foam.;The external and internal structure of foaming creamer powders was investigated with an electron scanning microscope. Next, the surface tension and foamability of various aqueous solutions were determined using the tensiolaminometric technique. An investigation of the foamability of a mixture of a milk protein and sucrose ester showed a synergistic effect.;After the microspheres of the powder are dissolved, the resulting foam may undergo decay arising either from liquid drainage, whether gravitational or due to interbubble gas diffusion, or from rupture of the interbubble liquid lamellae. In studying factors affecting foam stability, I focused on interbubble gas diffusion, which works against stability even given a stable lamella. I show that liquid drainage from the foam due to such diffusion (as distinct from that due to gravitation) can often be greatly reduced by adding a water-insoluble vapor to the foam-generating gas: the presence of such a vapor counterbalances the Ostwald ripening, thus stabilizing the system. The rate of disproportionation is governed not only by differences in Laplace pressure but also by the gas composition and the rheological behavior of the liquid-gas interface. The permeability of the interbubble lamellae also plays an important role.
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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.
