Thermodynamics of Hydrophobic Interaction of Dissymmetric Gemini Surfactants in Aqueous Solutions

• Published in: The journal of physical chemistry. B Vol. 106; no. 26; pp. 6614 - 6616
• Main Authors: Bai, Guangyue, Wang, Jinben, Wang, Yujie, Yan, Haike, Thomas, Robert K
• Format: Journal Article
• Language: English
• Published: American Chemical Society 04.07.2002
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp0143903

We have used microcalorimetry to measure the critical micelle concentrations (CMC) and enthalpies of micellization (ΔH mic) of the series of dissymmetric cationic gemini surfactants, [C m H2 m +1(CH3)2N(CH2)6N(CH3)2C n H2 n +1]Br2, designated as C m C6C n Br2, with constant n + m = 24 and n = 6, 8, 10, 11, 12. There is a small decrease in CMC as the ratio m/n increases but this decrease is not much larger than the error. On the other hand there is a very large decrease in the enthalpy of micellization with m/n. This is consistent with a large increase in the hydrophobic contribution to micellization with m/n. To explain the relative invariance of the CMC, there must be a corresponding large increase in the entropy of micellization with m/n. The change in the hydrophobic contribution is explained in terms of the relative strengths of internal and external hydrophobic contacts down the series.