Magnitudes of thermodynamic forces that result in the formation of giant micelles

Abstract

Giant micelles have properties similar to polymeric solutions, but the macromolecular configuration is transient, as their chains are renewed in breakage and recombination processes on a finite time scale. This imparts a unique rheological behavior, with applications in many areas of colloidal science. Giant micelles began to be studied in the 1980s, but it was only in 2015 that the first article was published in which an attempt was made to determine the enthalpy change (Hform) in isothermal calorimetric titration experiments. Giant micelles formed by the interaction of cationic surfactants with certain aromatic anions are the best studied systems. In addition to Hform, measurements of the values of Gform and TSform would allow us to quantitatively determine the driving forces that result in the formation of giant micelles when the two components are combined. However, in the mixture of the two components, in addition to water, four species will be present: the surfactant, the aromatic anion, and its two counter-ions. In this case, an aggregation model that allows determining the value of Gform becomes very complex. We have studied systems in which the two counter-ions are removed, using ion-exchange resins, forming acidic and basic species, with giant micelles subsequently formed by titration. The value of Gform referring to the formation of the giant micelle (complex salt), contains only two ions, and can be determined using the classical aggregation model for the formation of spherical micelles. In this project, we intend to develop thermodynamic studies involving the formation of giant micelles formed by the combination of cationic surfactant (TTA+) with benzoate derivatives (with the following atoms in position 4 of the aromatic ring: H, F, Cl, Br, I). The degrees of dissociation of the micelles, necessary to calculate Gform, will be determined by conductance measurements. Confirmation of the formation of giant micelles will be carried out using light scattering measurements.