The effect of electrolytes on the cloud point of ionic-nonionic surfactant solutions

Abstract

Cloud point measurements are reported for systems containing Triton X-100, water, electrolyte (NaCl or NaSCN) and ionic surfactant (sodium dodecyl sulfate). When ionic surfactant is added to an electrolyte-free Triton X-100 solution, the cloud point increases linearly as expected. However, when small amounts of electrolytes are added to the Triton X-100 solution in the presence of very low concentrations of sodium dodecyl sulfate (1 molecule per micelle) the cloud point curve decreases in a ratio depending on the concentration of electrolyte and the kind of co-ion. It is suggested that this effect is due to the change of counterion binding on the mixed ionic-nonionic micelles.