Hydrophilic and hydrophobic modifications of colloidal silica particles for Pickering emulsions

Sanna Björkegren; Lars Nordstierna; Anders Törncrona; Anders Palmqvist

doi:10.1016/j.jcis.2016.10.031

Hydrophilic and hydrophobic modifications of colloidal silica particles for Pickering emulsions

J Colloid Interface Sci. 2017 Feb 1:487:250-257. doi: 10.1016/j.jcis.2016.10.031. Epub 2016 Oct 15.

Authors

Sanna Björkegren¹, Lars Nordstierna², Anders Törncrona³, Anders Palmqvist²

Affiliations

¹ 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.
² Department of Chemistry and Chemical Engineering, Chalmers University of Technology, SE-412 96 Göteborg, Sweden.
³ AkzoNobel Pulp and Performance Chemicals AB, SE-445 80 Bohus, Sweden.

PMID: 27776283
DOI: 10.1016/j.jcis.2016.10.031

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).

Keywords: Controlled flocculation; Functionalized colloidal silica; Pickering emulsions.