Different responsiveness to hydrocarbons of linear and branched anionic/cationic-mixed wormlike surfactant micelles

For the first time, the responsiveness of mixed micelles of cationic and anionic surfactants to hydrocarbons was investigated. The micelles were prepared at different molar ratios of potassium oleate and n-octyltrimethylammonium bromide in salt-free water. It was shown that the viscoelastic solutions of the mixed micelles demonstrate a tremendous drop of viscosity by 4-6 orders of magnitude upon addition of a tiny amount of n-decane, which is due to the transformation of wormlike micelles into microemulsion droplets as was evidenced by SANS. Comparison of linear and branched micelles shows that unexpectedly, much larger amount of hydrocarbon was needed to induce the disruption of the network of branched micelles suggesting preferential solubilization of hydrocarbon inside the branching points. According to SANS data, at the excess of hydrocarbon, in both systems, the ellipsoid emulsion droplets are formed, which can be due to irregular distribution of the two surfactants on their surface.