Stabilisation of highly concentrated water-in-oil emulsions by polyhedral oligomeric silsesquioxane nanomolecules

Abstract

The material investigated is highly concentrated water-in-oil emulsion (w/o) with a dispersed phase concentration of approximately 90 wt%. Instability of such emulsions arises mostly from coalescence of the dispersed droplets in the system during ageing. Here, we report a new approach to stabilize this highly concentrated w/o emulsion by using Polyhedral Oligomeric Silsesquioxane (POSS) nanomolecules. POSS AM0275 nanomolecules were dissolved into the oil phase prior to both interfacial properties measurements and emulsification. A series of three industrial grade (Mosspar-H, Ash-H, Parprol) and one laboratory grade (Dodecane) oils were used. The interfacial tension, the interfacial elasticity and stability against coalescence of the resulting emulsions were investigated for varying oil type. The results showed that POSS AM0275 nanomolecules are surface actives. Interestingly the investigation clearly demonstrated that this nanomolecule can generate an interfacial layer with completely new properties that are not available neither with conventional surfactants nor nanoparticles. First, unlike nanoparticles, POSS nanomolecules significantly reduce the interfacial tension at the same extent as do surfactants. Second, both the interfacial tension and the interfacial elasticity measurements demonstrated that unlike surfactants, POSS AM0275 nanomolecule induces gelation of the interface resulting in the formation of a rigid and flexible gel-like bag which encapsulates the aqueous phase at such extent that one can suck out all the aqueous phase leaving an empty gel-like bag. Third, unlike nanoparticles, POSS AM0275 nanomolecules have a high capacity to form highly concentrated emulsions. The resulting emulsions demonstrated outstanding stability against coalescence though this was found to be sensitive to the type of oil used.