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Issue 3, 2016
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Oil-in-oil emulsions stabilised solely by solid particles

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Abstract

A brief review of the stabilisation of emulsions of two immiscible oils is given. We then describe the use of fumed silica particles coated with either hydrocarbon or fluorocarbon groups in acting as sole stabilisers of emulsions of various vegetable oils with linear silicone oils (PDMS) of different viscosity. Transitional phase inversion of emulsions, containing equal volumes of the two oils, from silicone-in-vegetable (S/V) to vegetable-in-silicone (V/S) occurs upon increasing the hydrophobicity of the particles. Close to inversion, emulsions are stable to coalescence and gravity-induced separation for at least one year. Increasing the viscosity of the silicone oil enables stable S/V emulsions to be prepared even with relatively hydrophilic particles. Predictions of emulsion type from calculated contact angles of a silica particle at the oil–oil interface are in agreement with experiment provided a small polar contribution to the surface energy of the oils is included. We also show that stable multiple emulsions of V/S/V can be prepared in a two-step procedure using two particle types of different hydrophobicity. At fixed particle concentration, catastrophic phase inversion of emulsions from V/S to S/V can be effected by increasing the volume fraction of vegetable oil. Finally, in the case of sunflower oil + 20 cS PDMS, the study is extended to particles other than silica which differ in chemical type, particle size and particle shape. Consistent with the above findings, we find that only sufficiently hydrophobic particles (clay, zinc oxide, silicone, calcium carbonate) can act as efficient V/S emulsion stabilisers.

Graphical abstract: Oil-in-oil emulsions stabilised solely by solid particles

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Publication details

The article was received on 30 Sep 2015, accepted on 04 Nov 2015 and first published on 09 Nov 2015


Article type: Paper
DOI: 10.1039/C5SM02438B
Citation: Soft Matter, 2016,12, 876-887
  • Open access: Creative Commons BY license
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    Oil-in-oil emulsions stabilised solely by solid particles

    B. P. Binks and A. T. Tyowua, Soft Matter, 2016, 12, 876
    DOI: 10.1039/C5SM02438B

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