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Effect of Ionic Strength on the Interfacial and Bulk Properties of Unsymmetrical Bolaamphiphiles
Author(s) -
Jiang Yurong,
Xu Zhigang,
Luan Jimei,
Liu Pingqin,
Qiao Weihong,
Li Zongshi
Publication year - 2008
Publication title -
journal of surfactants and detergents
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.349
H-Index - 48
eISSN - 1558-9293
pISSN - 1097-3958
DOI - 10.1007/s11743-007-1056-0
Subject(s) - chemistry , divalent , ionic strength , surface tension , pulmonary surfactant , micelle , molecule , ionic bonding , aqueous solution , sulfonate , ion , electrolyte , inorganic chemistry , salt (chemistry) , crystallography , sodium , organic chemistry , thermodynamics , biochemistry , physics , electrode
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 ω‐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 air—can 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.