Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10377992 | Journal of Colloid and Interface Science | 2005 | 6 Pages |
Abstract
Both thermodynamic and microenvironmental properties of the micelles for a series of cationic surfactants hexadecyltrimethylammonium (C16TAX) with different counterions, Fâ, Clâ, Brâ, NOâ3, and ½SO2â4, have been studied. Critical micelle concentration (CMC), degree of micelle ionization (α), and enthalpy of micellization (ÎHmic) have been obtained by conductivity measurements and isothermal titration microcalorimetry. Both the CMC and the α increase in the order SO2â4 < NOâ3 < Brâ < Clâ < Fâ, consistent with a decrease in binding of counterion, except for the divalent anion sulfate. ÎHmic becomes less negative through the sequence NOâ3 < Brâ < Clâ < Fâ < SO2â4, and even becomes positive for the divalent sulfate. The special behavior of sulfate is associated with both its divalency and its degree of dehydration. Gibbs free energies of micellization (ÎGmic) and entropies of micellization (ÎSmic) have been calculated from the values of ÎHmic, CMC, and α and can be rationalized in terms of the Hofmeister series. The variations in ÎHmic and ÎSmic have been compared with those for the corresponding series of gemini surfactants. Electron spin resonance has been used to assess the micropolarity and the microviscosity of the micelles. The results show that the microenvironment of the spin probe in the C16TAX surfactant micelles depends strongly on the binding of the counterion.
Related Topics
Physical Sciences and Engineering
Chemical Engineering
Colloid and Surface Chemistry
Authors
Nan Jiang, Peixun Li, Yilin Wang, Jinben Wang, Haike Yan, Robert K. Thomas,