title: Hydrophilic and hydrophobic modifications of colloidal silica particles for Pickering emulsions.
abstract: Colloidal silica particles, functionalized with hydrophilic and hydrophobic groups, have been studied for utilization in particle-stabilized emulsions, so called Pickering emulsions. The amounts of attached groups have been characterized using NMR spectroscopy and elemental analysis. A range of particles were prepared, with sizes from around 13 to 70nm in diameter. Hydrophilic functionalization of the silica sols was achieved by attaching methyl poly(ethylene glycol) (mPEG) silane to the silica particle surface. This provides a reduction of surface charge density, a pH dependent and controllable flocculation behavior and surface activity. The hydrophobic functionalization of the silica sols was accomplished by attaching organosilanes containing mainly propyl and methyl groups. The emulsification abilities were evaluated by preparing Pickering emulsions using particles, with varying degrees and combinations of surface functionalization, as stabilizers and comparing the obtained emulsion droplet size distributions. It was found that colloidal silica functionalized with hydrophobic groups produced emulsions with smaller droplets compared to using unmodified silica. The emulsification performance was further improved by the combination of both hydrophilic and hydrophobic groups. All particles having this heterogeneous modification were found to generate emulsions with high stability towards coalescence (from five weeks to 1.5 years).
authors: Department of Chemistry and Chemical Engineering, Chalmers University of Technology, SE-412 96 Göteborg, Sweden; AkzoNobel Pulp and Performance Chemicals AB, SE-445 80 Bohus, Sweden. Electronic address: sanna.bjorkegren@chalmers.se.
authors: Sanna
authors: S
authors: Björkegren
authors: Department of Chemistry and Chemical Engineering, Chalmers University of Technology, SE-412 96 Göteborg, Sweden.
authors: Lars
authors: L
authors: Nordstierna
authors: AkzoNobel Pulp and Performance Chemicals AB, SE-445 80 Bohus, Sweden.
authors: Anders
authors: A
authors: Törncrona
authors: Department of Chemistry and Chemical Engineering, Chalmers University of Technology, SE-412 96 Göteborg, Sweden.
authors: Anders
authors: A
authors: Palmqvist
keywords: Controlled flocculation; Functionalized colloidal silica; Pickering emulsions