MIXED MICELLE FORMATION OF ANIONIC AND NONIONIC SURFACTANTS

The effects of a series of nonionic surfactants, dodecyl polyoxyethylene ethers (DPE), on the micellization of an anionic surfactant, sodium dodecyl sulfate (NaDS), have been studied as a function of the mole ratio of NaDS DPE and of the polyoxyethylene chain length of the DPE molecule. Attention has been paid to changes in the degree of ionic dissociation of NaDS brought about by its incorporation in mixed micelles. The degree of ionic dissociation of the mixed micellar species was evaluated both from osmotic and pNa data. It has been shown that the degree of ionic dissociation of the ionic surface-active material in the mixed micelle increases as the proportion of the nonionic material increases and as the polyoxyethylene chain of the nonionic material is lengthened. The specific conductivities of the mixed solutions of NaDS and DPE at low concentrations are smaller than those of the solutions of NaDS alone, whereas at high concentrations the former are greater than the latter; the results would be explained by the degree of ionic dissociation and the mobility of the mixed micelles. © 1969.