title: Bespoke contrast-matched diblock copolymer nanoparticles enable the rational design of highly transparent Pickering double emulsions.
abstract: We report the preparation of highly transparent oil-in-water Pickering emulsions using contrast-matched organic nanoparticles. This is achieved via addition of judicious amounts of either sucrose or glycerol to an aqueous dispersion of poly(glycerol monomethacrylate)56-poly(2,2,2-trifluoroethyl methacrylate)500 [PGMA-PTFEMA] diblock copolymer nanoparticles prior to high shear homogenization with an equal volume of n-dodecane. The resulting Pickering emulsions comprise polydisperse n-dodecane droplets of 20-100 μm diameter and exhibit up to 96% transmittance across the visible spectrum. In contrast, control experiments using non-contrast-matched poly(glycerol monomethacrylate)56-poly(benzyl methacrylate)300 [PGMA56-PBzMA300] diblock copolymer nanoparticles as a Pickering emulsifier only produced conventional highly turbid emulsions. Thus contrast-matching of the two immiscible phases is a necessary but not sufficient condition for the preparation of highly transparent Pickering emulsions: it is essential to use isorefractive nanoparticles in order to minimize light scattering. Furthermore, highly transparent oil-in-water-in-oil Pickering double emulsions can be obtained by homogenizing the contrast-matched oil-in-water Pickering emulsion prepared using the PGMA56-PTFEMA500 nanoparticles with a contrast-matched dispersion of hydrophobic poly(lauryl methacrylate)39-poly(2,2,2-trifluoroethyl methacrylate)800 [PLMA39-PTFEMA800] diblock copolymer nanoparticles in n-dodecane. Finally, we show that an isorefractive oil-in-water Pickering emulsion enables fluorescence spectroscopy to be used to monitor the transport of water-insoluble small molecules (pyrene and benzophenone) between n-dodecane droplets. Such transport is significantly less efficient than that observed for the equivalent isorefractive surfactant-stabilized emulsion. Conventional turbid emulsions do not enable such a comparison to be made because the intense light scattering leads to substantial spectral attenuation.
authors.affiliation: Dainton Building, Department of Chemistry, The University of Sheffield, Brook Hill, Sheffield, S3 7HF, Yorkshire, UK. s.p.armes@sheffield.ac.uk mjrymaruk1@sheffield.ac.uk.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Rymaruk
authors.forename: Kate L
authors.initials: KL
authors.lastname: Thompson
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Derry
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Warren
authors.forename: Liam P D
authors.initials: LP
authors.lastname: Ratcliffe
authors.forename: Clive N
authors.initials: CN
authors.lastname: Williams
authors.forename: Steven L
authors.initials: SL
authors.lastname: Brown
authors.forename: Steven P
authors.initials: SP
authors.lastname: Armes