Structural investigation of CaAOT/water/oil microemulsions

The microstructural features of ternary microemulsions in the CaAOT/water/isooctane system are investigated by conductivity and NMR self-diffusion measurements. The results are compared with the corresponding NaAOT system. Experimental data are collected along water and oil dilution lines with the aim of investigating the interactions among the surfactant aggregates. Previous studies on the microemulsion regions of CaAOT/water/decane are also considered in order to evaluate the influence of the oil (branched or linear) on the microstructural transitions. Water-in-oil spherical droplets with a hard-sphere behavior are likely to occur in a very limited region of the L2 phase, namely, at low volume fractions of the disperse phase, φd. Both conductivity and water self-diffusion demonstrate the occurrence of important modifications of the water-in-oil droplet organization and suggest the occurrence of transient fusion-fission processes among the droplets. These processes become more and more important with increasing φd. The microstructure of the system is discussed in view of different approaches based on percolation theory, attractive interactions among discrete particles, and a multiconnected water network.