Interaction of the polysaccharide xanthan with surfactants in aqueous solution.
Item
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Title
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Interaction of the polysaccharide xanthan with surfactants in aqueous solution.
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Identifier
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AAI9108146
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identifier
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9108146
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Creator
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Mars, Laurent Robert.
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Contributor
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Adviser: Henri L. Rosano
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Date
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1990
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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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The extent and mechanism of the interaction of the polymer Xanthan, an anionic polysaccharide, with three types of surfactants, nonionic, anionic, and cationic has been investigated.;Interaction between Xanthan and a polyoxyethylene nonionic surfactant, Igepal CO-630, was found to occur when the surfactant is in its micellar form. Under conditions of salt concentration or pH that promote the helical conformation of Xanthan molecules, the degree of interaction is severely reduced, in fact becoming negligible. The proposed mechanism of interaction involves the formation of hydrogen bonds between the hydroxyl groups of Xanthan and the ether oxygens of the surfactant.;Evidence of a specific interaction between Xanthan and the anionic surfactant Sodium dodecylsulfate was found only when divalent cations were added to the solution. The pressure and potential isotherms of an insoluble anionic film (arachidic acid at pH = 10) are significantly altered when Xanthan is present along with Ca{dollar}\sp{lcub}2+{rcub}{dollar} ions in the subphase. In contrast, the presence of Xanthan alone in the subphase does not affect these isotherms.;A significant interaction was observed between Xanthan and the cationic surfactant Cetyltrimethylammonium bromide. Precipitation occurs under conditions of excess surfactant. Further addition of surfactant does not resolubilize the precipitate. In the pre-precipitation zone, the reduced viscosity of Xanthan solutions is lowered upon the addition of CTAB. This effect is comparable in magnitude to that produced by the addition of a simple salt (Tetramethylammonium chloride). The adsorption of CTAB on Xanthan therefore induces no surfactant-specific conformational change in the polysaccharide. The surface tension of CTAB solutions is lowered upon the addition of Xanthan. Similarly, the pressure-area isotherm of the cationic monolayer is expanded upon the introduction of Xanthan in the subphase. It is concluded that the increase in surface pressure is due to an ion-exchange reaction, with very little or no penetration of segments of the polysaccharide molecules into the hydrophobic region of the monolayer. A thermodynamic treatment of the interaction between Xanthan and the cationic monolayer is proposed. The values obtained for the changes in partial standard free energy, enthalpy, and entropy clearly show that the interaction between Xanthan and the cationic monolayer is entropy driven.
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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.
