Entropy 2010, 12(4), 983-995; doi:10.3390/e12040983
Article

Effect of Counterion and Configurational Entropy on the Surface Tension of Aqueous Solutions of Ionic Surfactant and Electrolyte Mixtures

1 Faculty of Pharmaceutical Sciences, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan 2 Center for Colloid and Interface Science, Research Institute for Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
* Author to whom correspondence should be addressed.
Received: 2 March 2010; in revised form: 10 April 2010 / Accepted: 17 April 2010 / Published: 23 April 2010
(This article belongs to the Special Issue Configurational Entropy)
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Abstract: In order to clarify the adsorption behavior of cationic surfactants on the air/aqueous electrolyte solution surface, we derived the theoretical equation for the surface tension. The equation includes the electrical work required for charging the air/water surface and the work attributable to the configurational entropy in the adsorbed film. By fitting the equation to the experimental data, we determined the binding constant between adsorbed surfactant ion and counterion, and found that the bromide ions, rather than the chloride ions, are preferentially adsorbed by the air/water surface. Furthermore, it was suggested that the contribution of configurational entropy to the surface tension is predominant in the presence of electrolytes because of the increase in the surface density of surfactant molecules associated with decreasing the repulsive interaction between their hydrophilic groups.
Keywords: surface tension; Helmholtz free energy; configurational entropy; adsorption constant; binding constant

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MDPI and ACS Style

Takata, Y.; Tagashira, H.; Hyono, A.; Ohshima, H. Effect of Counterion and Configurational Entropy on the Surface Tension of Aqueous Solutions of Ionic Surfactant and Electrolyte Mixtures. Entropy 2010, 12, 983-995.

AMA Style

Takata Y, Tagashira H, Hyono A, Ohshima H. Effect of Counterion and Configurational Entropy on the Surface Tension of Aqueous Solutions of Ionic Surfactant and Electrolyte Mixtures. Entropy. 2010; 12(4):983-995.

Chicago/Turabian Style

Takata, Youichi; Tagashira, Hiroaki; Hyono, Atsushi; Ohshima, Hiroyuki. 2010. "Effect of Counterion and Configurational Entropy on the Surface Tension of Aqueous Solutions of Ionic Surfactant and Electrolyte Mixtures." Entropy 12, no. 4: 983-995.

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