Odd/Even Effect in the Chain Length on the Enthalpy of Micellization of Gemini Surfactants in Aqueous Solution

• Published in: Langmuir Vol. 21; no. 15; pp. 6703 - 6706
• Main Authors: Li, Yajuan, Li, Peixun, Wang, Jinben, Wang, Yilin, Yan, Haike, Thomas, Robert K
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 19.07.2005
• Subjects: Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Micelles. Thin films; Enthalpy; Chain length; Cationic surfactant; Hydrophobicity; Microcalorimetry; Surfactant; Ionic surfactant; Micellar critical concentration; Alkyl; Titration curve; Aqueous solution; Thermodynamic properties; Physicochemical properties; Donor acceptor interaction; Micellization
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la050343g

The micellization properties of cationic symmetric gemini surfactants, [C m H2 m +1(CH3)2N(CH2)6N(CH3)2C m H2 m +1]Br2 (designated as C m C6C m Br2, with m = 7, 8, 9, 10, 11, 12, and 16), has been investigated by isothermal titration microcalorimetry. The critical micelle concentration (CMC) and enthalpy of micellization (ΔH mic) were determined from calorimetric titration curves. The linear decreasing of log CMC with increasing the length of the hydrophobic chain is consistent with an increase in the hydrophobicity of the alkyl chain. Interestingly, with increasing the length of the alkyl chain, the ΔH mic values of the surfactants with even numbered alkyl chains vary from endothermic to exothermic, whereas the ΔH mic values of the surfactants with odd numbered alkyl chains are all endothermic and tend to become more endothermic. The pronounced even/odd effect in ΔH mic is discussed with respect to the “donor−acceptor” interaction.