MICROEMULSIONS AND THEIR RELATION TO SWOLLEN MICELLAR SOLUTIONS.
Item
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Title
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MICROEMULSIONS AND THEIR RELATION TO SWOLLEN MICELLAR SOLUTIONS.
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Identifier
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AAI8614665
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identifier
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8614665
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Creator
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CAVALLO, JOHN LOUIS.
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Contributor
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Henri L. Rosano
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Date
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1986
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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 thermodynamic stability of microemulsion systems and their relation to swollen micellar solutions have been investigated. The results obtained suggest that the apparent path-dependent properties sometimes observed during microemulsion formation may be explained by the small free energy values involved in transforming an emulsion into a microemulsion. These results suggest that the right order of mixing the various components plays a major role in lowering the activation energy barriers these systems must overcome during their formation. Based on these results it is concluded that microemulsions are thermodynamically stable systems.;Emulsions (5 o/w; 1 w/o) prepared with oil, water and surfactant were titrated to clarity with a cosurfactant. The volume of the continuous phase was varied from 10 to 60 ml. The mole fractions of cosurfactant/surfactant and cosurfactant/continuous phase was determined at various temperatures (15 to 55(DEGREES)C). At 30(DEGREES)C, free energy and enthalpy changes accompanying cosurfactant adsorption during microemulsion formation were found to vary from -19.6 to -6.4 kJ/mole respectively. Entropy of formation changes were found to be positive in 5 cases from 3.5 x 10('-2) to 8.3 x 10('-2) kJ/K mole and in one case negative -1.8 x 10('-2) kJ/K mole. These results indicate that microemulsion formation is a spontaneous process, however the driving force is small. O/W emulsions of long chain sulfate/n-hydrocarbon/5% NaCl were titrated to clarity (85% transmittance or better) with long chain dimethylamine oxide.;During the titration of the emulsions with a cosurfactant, just before clearing, the system undergoes viscosity changes due to the formation and resolution of filament structure into microdroplets. After each addition of cosurfactant, systems prepared with a constant amount of water, oil and surfactant were allowed to equilibrate and phase separation was observed. From these results it is concluded that O/W microemulsions may be described as hydropathic oleomicellar solutions.;The vapor pressure of five O/W microemulsion systems was determined as a function of increasing the volume of hydrocarbon in the dispersed phase using an isoteniscope. At low volume fractions of hydrocarbon, the microemulsion droplets behave like large molecules in solution. Beyond a certain hydrocarbon volume fraction, the droplets are less stable. The energy of activation corresponding to the breaking of the interfacial sheath was found to be between 35.2 and 20.9 kJ/mole. (Abstract shortened with permission of author.).
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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.
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Program
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Chemistry
