Nonaqueous CO2-philic surfactants thermodynamics: aggregation and formation of microemulsions in supercritical CO2

• Grant number: 05/03607-7
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Effective date (Start): February 01, 2006
• Effective date (End): October 02, 2006
• Field of knowledge: Physical Sciences and Mathematics - Chemistry
• Principal Investigator: Watson Loh
• Grantee: Alexandre Gurgel
• Host Institution: Instituto de Química (IQ). Universidade Estadual de Campinas (UNICAMP). Campinas , SP, Brazil

Abstract

The physico-chemical characterization of micelle surfactant solutions, both with or without additives, requires the determination of thermodynamic parameters, such as enthalpy, entropy and Gibbs free energy, providing information about its formation mechanism. The complementary use of different analytical methods may yield direct data about those systems. In view of this, the growing interest in understanding the way in which micellization of different surfactant structures occurs in several solvents may be satisfied by an approach employing calorimetric techniques with the help of more refined strucutral investigations, namely light, X-ray or neutron scattering measurements. This project contemplates the use of isothermic titration calorimetry on the study of nonionic, “CO2-philic” surfactants micellization in nonaqueous media with a low cohesive energy. The effects of variation of temperature and surfactant molecule structure on the micellization thermodynamics will be accounted for during the investigation. Direct structural information, such as shape and size of the aggregates, will be obtained by small-angle X-ray scattering (SAXS). By using silicone solvents to disperse the surfactants, especially selected with regards to the presence of certain chemical moieties in their molecules, the project aims to characterize pressure-temperature phase diagrams that may be useful in researches on the formation of self-assembled systems in a nonaqueous solvent with a high industrial potential: supercritical CO2 (scCO2). The results acquired thereafter will be valuable to guide the assembly of a pressurized apparatus that allows for the performance of SAXS analyses with aggregated systems in scCO2, hence providing important information about their size and shape. (AU)