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Effect of Compressed CO 2 on the Critical Micelle Concentration and Aggregation Number of AOT Reverse Micelles in Isooctane
Author(s) -
Chen Jing,
Zhang Jianling,
Han Buxing,
Feng Xiaoying,
Hou Minqiang,
Li Wenjing,
Zhang Zhaofu
Publication year - 2006
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200501593
Subject(s) - micelle , aggregation number , critical micelle concentration , chemistry , chemical engineering , chromatography , organic chemistry , engineering , aqueous solution
The effect of compressed CO 2 on the critical micelle concentration (cmc) and aggregation number of sodium bis‐2‐ethylhexylsulfosuccinate (AOT) reverse micelles in isooctane solution was studied by UV/Vis and florescence spectroscopy methods in the temperature range of 303.2–318.2 K and at different pressures or mole fractions of CO 2 ( X CO 2). The capacity of the reverse micelles to solubilize water was also determined by direct observation. The standard Gibbs free energy (Δ ${G{{{\rm m}\hfill \atop {^\circ}\hfill}}}$ ), standard enthalpy (Δ ${H{{{\rm m}\hfill \atop {^\circ}\hfill}}}$ ), and standard entropy (Δ ${S{{{\rm m}\hfill \atop {^\circ}\hfill}}}$ ) for the formation of the reverse micelles were calculated by using the cmc data determined. It was discovered that the cmc versus X CO 2curve and the Δ ${G{{{_{{\rm m}}}\hfill \atop {^\circ}\hfill}}}$ versus X CO 2curve for a fixed temperature have a minimum, and the aggregation number and water‐solubilization capacity of the reverse micelles reach a maximum at the X CO 2value corresponding to that minimum. These results indicate that CO 2 at a suitable concentration favors the formation of and can stabilize AOT reverse micelles. A detailed thermodynamic study showed that the driving force for the formation of the reverse micelles is entropy.