Relationship between interfacial properties and formation of microemulsions and emulsions of water and supercritical carbon dioxide

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dc.contributor.advisorJohnson, Keith P.en
dc.creatorPsathas, Petrosen
dc.date.accessioned2011-03-31T17:35:01Zen
dc.date.available2011-03-31T17:35:01Zen
dc.date.issued2001-08en
dc.descriptiontexten
dc.description.abstractThe utilization of supercritical (SC) CO2 as an alternative green solvent has attracted significant research devotion in the last decade. Its uniqueness lies on the fact that CO2 is a non-FDA regulated solvent mainly generated as the sideproduct of industrial process, is easily recyclable, readily available, non flammable and essentially non toxic. Dense CO2 is non-polar (unlike water), has weak van der Waals forces (unlike oils) and as such may be considered a third type of fluid phase in nature, somewhat similar to fluorocarbons. The use of SC CO2 has expanded into broad technological areas one of which is the stabilization of water-in-CO2 dispersions that offer new possibilities for separations on the basis of polarity, and as media for reactions between polar and nonpolar molecules. The formation of stable emulsions of water-in-CO2 (W/C) so far has been hampered by the lack of suitable surfactants. The synthesis of various molecularly engineered surfactants is demonstrated in this study, among which are polydimethylsiloxane (PDMS)-based block copolymer ionomers, ionic and nonionic perfluoropolyether (PFPE) and nonionic perfluorooctylmethacrylate (PFOMA)-based ones. The concentrated W/C emulsions are characterized with electrical conductivity, optical microscopy and multiwavelength turbidity technique. The emulsion stability is assessed as a function of formulation variables that influence the surfactant monolayer curvature, such as temperature, pH, salinity and pressure. The response of the interfacial activity of the surfactant to changes in the variables above is monitored with interfacial tension (γ) measurements and is correlated to emulsion stability. Moreover, salinity is used to tune the surfactant aggregation characteristics, resulting in spontaneous microemulsion formation upon crossing the critical microemulsion concentration (cµc). Based on guidelines provided by γ versus temperature, stable concentrated (50:50 by mass) C/W miniemulsions consisting of 200 nm droplets are formed with the phase inversion temperature (PIT) method. Finally, the formation of unflocculated and stable dilute W/C emulsions is studied with a homologous series of PFOMA-based nonionic surfactants, and mapping of γ with surfactant hydrophilicity provide useful pathways for the synthesis of the optimum structure.
dc.description.departmentChemical Engineeringen
dc.format.mediumelectronicen
dc.identifier.urihttp://hdl.handle.net/2152/10790en
dc.language.isoengen
dc.rightsCopyright is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works.en
dc.rights.restrictionRestricteden
dc.subjectEmulsionsen
dc.subjectWater--Analysisen
dc.subjectSupercritical fluidsen
dc.subjectCarbon dioxide--Analysisen
dc.titleRelationship between interfacial properties and formation of microemulsions and emulsions of water and supercritical carbon dioxideen
thesis.degree.departmentChemical Engineeringen
thesis.degree.disciplineChemical Engineeringen
thesis.degree.grantorThe University of Texas at Austinen
thesis.degree.levelDoctoralen
thesis.degree.nameDoctor of Philosophyen

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