Enthalpy–Entropy Compensation Phenomenon Observed for Different Surfactants in Aqueous Solution

ISSN： 0021-9797

Source： Journal of Colloid and Interface Science, Vol.219, Iss.1, 1999-11, pp. : 31-36

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Abstract

Based on previously reported thermodynamic data such as changes of the Gibbs energy (ΔG_m^°), the enthalpy (ΔH_m^°), and the entropy (ΔS_m^°) on micelle formation of more than 15 species of surfactants (including nonionic, anionic, and cationic surfactants), plots of ΔH_m^° vs ΔS_m^° (not of ΔS_m^° vs ΔH_m^°, as is usually done) were made. For each surfactant, a linear relation having almost the same slope (1/307 K^-1) within a small error (±2.3%) but a different intercept (ς) depending on the surfactant species was obtained, i.e., ΔS_m^° = (1/307)ΔH_m^° + ς, where 1/307 (K^-1) means that the so-called compensation temperature (T_C) is 307 K. Strictly speaking, T_C ranges from 299 to 315 K, depending on the species. The intercept corresponds to the entropy change at a specific temperature giving ΔH_m^° = 0, at which the driving force of micelle formation comes only from the entropy term; this temperature is characteristic of the surfactant species. On the other hand, the compensation temperature has no significant meaning other than a mean temperature studied.