Effect of Nanoparticle Hydrophobicity on Stability of Highly Concentrated Emulsions
JOURNAL OF DISPERSION SCIENCE AND TECHNOLOGY(2014)
摘要
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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关键词
Crystallization,emulsions,fumed nanosilica,stability,surfactant
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