title: Synergistic formation and stabilization of oil-in-water emulsions by a weakly interacting mixture of zwitterionic surfactant and silica nanoparticles.
abstract: Oil-in-water emulsions were formed and stabilized at low amphiphile concentrations by combining hydrophilic nanoparticles (NPs) (i.e., bare colloidal silica) with a weakly interacting zwitterionic surfactant, caprylamidopropyl betaine, to generate a high hydrophilic-lipophilic balance. The weak interaction of the NPs with surfactant was quantified with contact angle measurements. Emulsions were characterized by static light scattering to determine the droplet size distributions, optical photography to quantify phase separation due to creaming, and both optical and electron microscopy to determine emulsion microstructure. The NPs and surfactant acted synergistically to produce finer emulsions with a greater stability to coalescence relative to the behavior with either NPs or surfactant alone. As a consequence of the weak adsorption of the highly hydrophilic surfactant on the anionic NPs along with the high critical micelle concentration, an unusually large surfactant concentration was available to adsorb at the oil-water interface and lower the interfacial tension. The synergy for emulsion formation and stabilization for the two amphiphiles was even greater in the case of a high-salinity synthetic seawater aqueous phase. Here, higher NP adsorption at the oil-water interface was caused by electrostatic screening of interactions between (1) NPs and the anionic oil-water interface and (2) between the NPs. This greater adsorption as well as partial flocculation of the NPs provided a more efficient barrier to droplet coalescence.
authors.affiliation: McKetta Department of Chemical Engineering, ‡Department of Chemistry and Biochemistry, and §Department of Petroleum and Geosystems Engineering, University of Texas at Austin , Austin, Texas 78712-0231, United States.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Worthen
authors.forename: Lynn M
authors.initials: LM
authors.lastname: Foster
authors.forename: Jiannan
authors.initials: J
authors.lastname: Dong
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Bollinger
authors.forename: Adam H
authors.initials: AH
authors.lastname: Peterman
authors.forename: Lucinda E
authors.initials: LE
authors.lastname: Pastora
authors.forename: Steven L
authors.initials: SL
authors.lastname: Bryant
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Truskett
authors.forename: Christopher W
authors.initials: CW
authors.lastname: Bielawski
authors.forename: Keith P
authors.initials: KP
authors.lastname: Johnston
mesh_terms: D004655:Emulsions; D057927:Hydrophobic and Hydrophilic Interactions; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D009821:Oils / Q000737:chemistry*; D010316:Particle Size; D012822:Silicon Dioxide / Q000737:chemistry*; D013499:Surface Properties; D013500:Surface Tension; D013501:Surface-Active Agents / Q000737:chemistry*; D050337:Trimethyl Ammonium Compounds / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D004655:Emulsions; D009821:Oils; D013501:Surface-Active Agents; D050337:Trimethyl Ammonium Compounds; D014867:Water; D012822:Silicon Dioxide