Highly concentrated oil-in-water (O/W) emulsions stabilized by catanionic surfactants

The abilities of a series of catanionic surfactants (catanionics) to emulsify paraffin oil/water (PO/H2O) mixtures have been investigated. It was found that catanionics with head-to-tail structures are efficient emulsifiers, including tetradecyltrimethylammonium laurate (TTAL), decyltrimethylammonium laurate (D(10)TAL) and 1-methyl-3-decyl-immidazolium laurate (1-M-3-D-10-ImL). Stable oil-in-water (O/W) emulsions were obtained by simple hand-shaking at low water content (down to 6% by volume), as confirmed by visual inspection, optical microscopy observations, conductivity measurements and confocal fluorescence microscopy observations. The emulsion droplets are closely-packed, imparting the samples viscoelastic properties as proved by rheological measurements. The emulsions could not be destroyed at elevated temperatures and interestingly, a slight increase of viscoelasticity was observed. Specifically for TTAL which was prepared by acid-base neutralization between tetradecyltrimethylammonium hydroxide (TTAOH) and lauric acid (LA), the influence of the composition of the ion-pair was also investigated. While the properties of the emulsions can be only slightly influenced at LA-rich side, significant influence was noted at TTAOH-rich side. We have also checked the emulsifying ability of a pseudogemini catanionic surfactant, bis(tetradecyltrimethylammonium) adipate ((TTA)(2)A), and found it could not emulsify PO/H2O mixtures under the same experimental conditions, indicating that the architecture of the catanionics also has a profound influence. (C) 2016 Elsevier B.V. All rights reserved.