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

✍ Scribed by Gohsuke Sugihara; Mihoko Hisatomi

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 81 KB
• Volume: 219
• Category: Article
• ISSN: 0021-9797
• DOI: 10.1006/jcis.1999.6378

✦ Synopsis

Based on previously reported thermodynamic data such as changes of the Gibbs energy (⌬G°m), the enthalpy (⌬H °m), and the entropy (⌬S°m) on micelle formation of more than 15 species of surfactants (including nonionic, anionic, and cationic surfactants), plots of ⌬H °m vs ⌬S°m (not of ⌬S°m vs ⌬H °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 () depending on the surfactant species was obtained, i.e., ⌬S°m ‫؍‬ (1/307)⌬H °m ؉ , 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 ⌬H °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.