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Issue 1, 2017
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Pickering emulsions stabilized by coloured organic pigment particles

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Abstract

The possibility of stabilizing emulsions of water and non-polar alkane with pure, coloured organic pigment particles is explored. Seven pigment types each possessing a primary colour of the rainbow were selected. Their solubility in water or heptane was determined using a spectrophotometric method and their surface energies were derived from the contact angles of probe liquids on compressed disks of the particles. As expected, most of the pigments are relatively hydrophobic but pigment orange is quite hydrophilic. At equal volumes of oil and water, preferred emulsions were water-in-oil (w/o) for six pigment types and oil-in-water (o/w) for pigment orange. The emulsion type is in line with calculated contact angles of the particles at the oil–water interface being either side of 90°. Their stability to coalescence increases with particle concentration. Emulsions are shown to undergo limited coalescence from which the coverage of drop interfaces by particles has been determined. In a few cases, close-packed primary particles are visible around emulsion droplets. At constant particle concentration, the influence of the volume fraction of water (ϕw) on emulsions was also studied. For the most hydrophilic pigment orange, emulsions are o/w at all ϕw, whereas they are w/o for the most hydrophobic pigments (red, yellow, green and blue). For pigments of intermediate hydrophobicity however (indigo and violet), catastrophic phase inversion becomes possible with emulsions inverting from w/o to o/w upon increasing ϕw. For the first time, we link the pigment surface energy to the propensity of emulsions to phase invert transitionally or catastrophically.

Graphical abstract: Pickering emulsions stabilized by coloured organic pigment particles

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Publication details

The article was received on 13 Jul 2016, accepted on 10 Sep 2016 and first published on 19 Sep 2016


Article type: Edge Article
DOI: 10.1039/C6SC03085H
Citation: Chem. Sci., 2017,8, 708-723
  • Open access: Creative Commons BY license
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    Pickering emulsions stabilized by coloured organic pigment particles

    B. P. Binks and S. O. Olusanya, Chem. Sci., 2017, 8, 708
    DOI: 10.1039/C6SC03085H

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