Thermodynamics of micellization of homologous series of alkyl mono and di-glucosides in water and in heavy water

Abstract

In this study, isothermal titration calorimetry was used to follow the micellization of two homologous series of alkylglucoside surfactants from heptyl to nonylmonoglucosides and from octyl to dodecyldiglucosides over the temperature range from (15 to 65)°C. These measurements allowed the calculation of the thermodynamic parameters associated with micelle formation, viz.: Gibbs free energy, enthalpy, entropy and heat capacity changes. Moreover, micellization of one of these surfactants, nonylmonoglucoside, was also investigated in heavy water, D2O, at different temperatures for comparison.Overall, these results conformed very well with the behaviour displayed by other surfactants with respect to changes within the homologous series. Use of additivity schemes provided estimates of contributions from the polar head group and the methylene units to these thermodynamic functions. The good agreement between the results for alkylglucosides micellization and literature data for other surfactants confirms that, with respect to the hydrophobic interior, their micelles display similar properties. The same can be said about the temperature dependence for micellization, which follows that of other surfactants. Two specific issues were investigated. First the contributions from one versus two glucoside units in the surfactant chemical structure were assessed, which turned out to be essentially the same because the data for the two families of surfactants could be superimposed within their experimental uncertainty. The second addressed possible differences regarding micelle formation in normal and heavy water. In this respect, data for the micellization of one of these surfactants provided values for the thermodynamic functions in D2O that could be considered only slightly different from those in H2O.