Pickering emulsions stabilized by coloured organic pigment particles

Binks, Bernard P; Olusanya, Samuel

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.  

Citation

Binks, B. P., & Olusanya, S. (2017). Pickering emulsions stabilized by coloured organic pigment particles. Chemical science, 8(1), 708-723. https://doi.org/10.1039/C6SC03085H

• Journal Article Type: Article
• Acceptance Date: Sep 10, 2016
• Online Publication Date: Sep 19, 2016
• Publication Date: 2017-01
• Deposit Date: Sep 15, 2016
• Publicly Available Date: Sep 19, 2016
• Journal: Chemical science
• Print ISSN: 2041-6520
• Electronic ISSN: 2041-6539
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 8
• Issue: 1
• Pages: 708-723
• DOI: https://doi.org/10.1039/C6SC03085H
• Keywords: Pickering emulsions
• Public URL: https://hull-repository.worktribe.com/output/443113
• Publisher URL: http://pubs.rsc.org/en/content/articlelanding/2016/sc/c6sc03085h#!divAbstract
• Additional Information: This is a copy of an open access article which has been accepted for future publication in: Chemical science, 2017, v.8, issue 1.