Effect of Ionic Strength on the Interfacial and Bulk Properties of Unsymmetrical Bolaamphiphiles

Abstract

By performing measurements of the equilibrium surface tensions of electrolyte solutions of three unsymmetrical bolaamphiphiles, each of which has an aromatic ring and a x-carboxyalkyl chain in its molecular structure, we conclude that the carboxyl and sulfonate groups at both ends of the molecule-which enter the solution while the hydrophobic chain extends into the aircan force these surfactants to adopt a looped configuration which looks like the letter ''U'' upside-down, resulting in regular arrangements at the air/water interface and micelles in bulk solution. Surface tension measurements of these surfactants as a function of added salt reveal the limiting surface tension to be less sensitive to the ionic strength in LiCl solution and significantly sensitive to divalent Ca 2+ and Mg 2+ ions in hard water. This result reveals that the looped configuration of the molecule is the dominant factor in determining whether the molecules of this surfactant are sensitive to ionic strength or not. This paper also reports briefly on the effect of the interactions of divalent Ca 2+ and Mg 2+ ions with unsymmetrical bolaamphiphiles on the turbidity of hard water. These results suggest that the interactions of divalent Ca 2+ and Mg 2+ ions with carboxyl groups are strong, and the two breaks in the surface tension curves disappear. In 200 ppm hard water, the turbidity appears over just a small range of surfactant concentrations, showing that the presence of the Ca 2+ and Mg 2+ ions has little effect on the application of these surfactants.

Interfacial Tension of Unsymmetrical Bolaamphiphile Surfactant in Surfactant/Alkali/Crude Oil Systems

“…According to the molecular structure of oleic acid, a novel surfactant, in which the replacements of fluorocarbon residues and nonionic head groups with the aromatic rings of better planarity and rigidity, and the ionic head groups (carboxyl group of oleic acid) of better hydrophilic properties, respectively, is designed, and some additional surface properties are to be expected. As predicted, these surfactants exhibit unusually low limit surface tensions, about 20 mN m 1 , equal to or even lower than that of some fluorocarbon surfactants, let alone that of hydrocarbon surfactants (Jiang et al, 2008). Moreover, the surface tension measurements of these surfactants indicate the existence of two discontinuities, referred to as the "first CMC" and the second CMC, similar to the conventional bolaform surfactants.…”

Palm‐Based Nonionic Surfactants as Emulsifiers for High Internal Phase Emulsions

“…Surface activity and micellar properties of surfactants [1][2][3][4][5][6][7] are of potential importance and scientific interest. Surfactants micellize in solution after reaching a critical concentration depending on their molecular structure and environmental conditions [8,9].…”