Journal
JOURNAL OF DISPERSION SCIENCE AND TECHNOLOGY
Volume 35, Issue 2, Pages 283-292Publisher
TAYLOR & FRANCIS INC
DOI: 10.1080/01932691.2013.775584
Keywords
Crystallization; emulsions; fumed nanosilica; stability; surfactant
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The effect of hydrophobicity index (HI) of fumed nanosilica specimens on stability of water-in-oil (W/O) highly concentrated emulsions (HCE with phi=90vol%) with an overcooled dispersed phase was studied. A series of five silica with HI in the 0.60-1.34 range and HI>3 were used separately and in combination with a low molecular weight traditional surfactant, Sorbitan MonoOleate (SMO). First, it was shown that SMO alone can stabilize W/O HCE whereas only silica nanoparticles with intermediate HI in the range 0.97HI1.34 could form W/O emulsions only up to 77-79vol%. Then, on the contrary to SMO-based emulsions, Pickering emulsions are unstable under shearing. When mixed (silica plus SMO) emulsifier systems were used, firstly a thermodynamic consideration revealed that only SMO is likely to adsorb at the W/O interface and controls the emulsifying process by the decrease in the interfacial tension. Then, interestingly, all different kinds of emulsion stability investigated in this study demonstrate a breaking point (BP) at HI=0.97. Below the BP the emulsions were found to be very unstable on shelf as well as under shear. Above the BP, a clear synergy between colloidal silica and SMO surfactant has been found.
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