title: Measurements of Submicron Particle Adsorption and Particle Film Elasticity at Oil-Water Interfaces.
abstract: The influence of particle adsorption on liquid/liquid interfacial tension is not well understood, and much previous research has suggested conflicting behaviors. In this paper we investigate the surface activity and adsorption kinetics of charge stabilized and pH-responsive polymer stabilized colloids at oil/water interfaces using two tensiometry techniques: (i) pendant drop and (ii) microtensiometer. We found, using both techniques, that charge stabilized particles had little or no influence on the (dynamic) interfacial tension, although dense silica particles affected the "apparent" measured tension in the pendent drop, due to gravity driven elongation of the droplet profile. Nevertheless, this apparent change additionally allowed the study of adsorption kinetics, which was related qualitatively between particle systems by estimated diffusion coefficients. Significant and real interfacial tension responses were measured using ∼53 nm core-shell latex particles with a pH-responsive polymer stabilizer of poly(methyl methacrylate)-b-poly(2-(dimethylamino)ethyl methacrylate) (pMMA-b-pDMAEMA) diblock copolymer. At pH 2, where the polymer is strongly charged, behavior was similar to that of the bare charge-stabilized particles, showing little change in the interfacial tension. At pH 10, where the polymer is discharged and poorly soluble in water, a significant decrease in the measured interfacial tension commensurate with strong adsorption at the oil-water interface was seen, which was similar in magnitude to the surface activity of the free polymer. These results were both confirmed through droplet profile and microtensiometry experiments. Dilational elasticity measurements were also performed by oscillation of the droplet; again, changes in interfacial tension with droplet oscillation were only seen with the responsive particles at pH 10. Frequency sweeps were performed to ascertain the dilational elasticity modulus, with measured values being significantly higher than previously reported for nanoparticle and surfactant systems, and similar in magnitude to protein stabilized droplets.
authors.affiliation: School of Chemical and Process Engineering, University of Leeds , Woodhouse Lane, Leeds LS2 9JT, United Kingdom.
authors.forename: Mohamed S
authors.initials: MS
authors.lastname: Manga
authors.affiliation: School of Chemical and Process Engineering, University of Leeds , Woodhouse Lane, Leeds LS2 9JT, United Kingdom.
authors.forename: Timothy N
authors.initials: TN
authors.lastname: Hunter
authors.affiliation: School of Chemical and Process Engineering, University of Leeds , Woodhouse Lane, Leeds LS2 9JT, United Kingdom.
authors.forename: Olivier J
authors.initials: OJ
authors.lastname: Cayre
authors.affiliation: School of Chemical and Process Engineering, University of Leeds , Woodhouse Lane, Leeds LS2 9JT, United Kingdom.
authors.forename: David W
authors.initials: DW
authors.lastname: York
authors.affiliation: Department of Chemical Engineering, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Reichert
authors.affiliation: Department of Chemical Engineering, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States.
authors.forename: Shelly L
authors.initials: SL
authors.lastname: Anna
authors.affiliation: Department of Chemical Engineering, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States.
authors.forename: Lynn M
authors.initials: LM
authors.lastname: Walker
authors.affiliation: School of Chemical and Process Engineering, University of Leeds , Woodhouse Lane, Leeds LS2 9JT, United Kingdom.|Heriot-Watt University, George Heriot Wing , Edinburgh, EH14 4AS, United Kingdom.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Williams
authors.affiliation: School of Chemical and Process Engineering, University of Leeds , Woodhouse Lane, Leeds LS2 9JT, United Kingdom.|School of Chemical Engineering, The University of Queensland , Brisbane, Queensland 4072, Australia.
authors.forename: Simon R
authors.initials: SR
authors.lastname: Biggs