Ions specific effect in colloidal systems: combining experimental data and theoretical modeling

Abstract

Amphiphile aggregates show properties, such as stability and shape, which depend upon the concentration and the nature of the ions in solution. This effect is general and applies to systems ranging from the self-assemblies of surfactants (micelles) to lamellae formed by double hydroxide. Although the specific ion effects were first described more than a hundred years ago, there is no consensus in a theoretical formulation, valid for different systems, to explain the determination of the properties of aggregates by the ion's nature. A theory capable of predicting the properties of the aggregates in the presence of different salts would be of major interest to fields ranging from biological membranes to optically active metallic nanoparticles. The formulation of such a theory depends upon the determination of the forces which control the effects of ions in the various systems. The presence of trifluoromethanesulfonate (triflate, Tf) salts in some systems (micelles, gold nanoparticles, double layered hydroxide, DNA gel particles) led to unexpected effects. Triflate salts produced changes in shape and interfacial properties of particles and, as consequence, provided information upon the origin of ion specific effects on interfaces. In this Project, we will determine properties of zwitterionic micelles, vesicles and cationic micelles in the presence of triflate and anions with analogous structures, using a wide range of techniques. We will combine experimental results to theoretical modeling, providing conceptual bases to the observed effects, allowing for a quantitative and qualitative concept. These results will contribute to a general understanding of specific binding of ions at interfaces and the following promoted changes, problem known as "Hofmeister series". (AU)