A comparative study of the physicochemical properties of perfluorinated and hydrogenated amphiphiles

• Published in: Journal of colloid and interface science 2005-08, Vol.288 (1), p.247-260
• Main Authors: Blanco, Elena, González-Pérez, Alfredo, Ruso, Juan M., Pedrido, Rosa, Prieto, Gerardo, Sarmiento, Félix
• Format: Article
• Language: English
• Subjects: Algorithms; Biomedical Research; Caprylates - chemistry; Chemistry; Colloidal state and disperse state; Critical micelle concentration minimum; Decanoates - chemistry; Exact sciences and technology; Fluorocarbons - chemistry; General and physical chemistry; Hydrogenated; Hydrogenation; Krafft point; Laurates - chemistry; Micelles; Micelles. Thin films; Perfluorinated; Thermodynamics
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2005.02.085

In this work we studied and compared the physicochemical properties of perfluorinated (sodium perfluoroheptanoate, C7FONa, and perfluorooctanoate, C8FONa) and hydrogenated (sodium octanoate, C8HONa, decanoate, C10HONa, and dodecanoate, C12HONa) amphiphiles. First, we determined their Krafft points to study the solubility and appropriate temperature range of micellization of these compounds. The critical micelle concentration (cmc) and ionization degree of micellization ( β) as a function of temperature ( T) were estimated from conductivity data. Plots of cmc vs T appear to follow the typical U-shaped curve with a minimum T min . The results show that the surfactants with CF 2/CH 2 ratio of 1.5 between alkyl chains (C12HONa–C8FONa and C10HONa–C7FONa) have nearly the same minimum value for cmc against temperature. The comparison between the cmc of hydrogenated amphiphiles and the corresponding perfluorinated amphiphiles must be done at this point. Thermodynamic functions of micellization were obtained by applying different theoretical models and choosing the one that best fit our experimental data. Although perfluorinated and hydrogenated amphiphiles present similar thermodynamic behavior, we have found a variation of 1.3 to 1.7 in the CF 2/CH 2 ratio, which did not remain constant with temperature. In the second part of this study the apparent molar volumes and adiabatic compressibilities were determined from density and ultrasound velocity measurements. Apparent molar volumes at infinite dilution presented the ratio 1.5 between alkyl chains again. However, apparent molar volumes upon micellization for sodium perfluoroheptanoate indicated a different aggregation pattern.