Effect of salt concentration on interfacial behavior in the surfactant system water+n-octadecane+diethylene glycol monohexyl ether

We study the phase behavior and observe wetting and nonwetting behaviors, as well as the wetting transition which occurs in the four-component surfactant system water+n-octadecane+diethylene glycol monohexyl ether+NaCl. All experiments are performed at constant weight ratio of water:n-octadecane (1:1) and constant temperature 35.0±0.05 °C, with varying NaCl concentration. It is found that the system water+n-octadecane+C6E2 exhibits a wetting transition lying at 17.1 wt. % of NaCl in water. This observation is further confirmed by interfacial tension measurements. In addition to that of lyotropic salt (NaCl), the effect of hydrotropic salt on the interfacial wetting transition is also discussed.