Interactions between Hexaoxyethylene Glycol Dodecyl Ether and Anionic Surfactants

Interactions of a nonionic surfactant such as hexaoxyethylene glycol dodecyl ether (6 ED) with several anionic surfactants were investigated by measuring the absorption spectra of aqueous triiodide ion (I-3) solutions and surface tension. Two anionic surfactants, sodium dodecyl sulfate (SDS) and sodium 4-sulf obutyl laurate (11 C-4), were compared for their structural effects on I-3 -6 ED complex formation by mixing nonionic and anionic surfactants. The maximum absorption wavelength of I-3-6 ED shifted, and absorbance decreased in all cases with increase in the concentration of the added anionic surfactant. Two break points, A and B, were observed in a plot of maximum absorption wavelength against the anionic surfactant concentration. The slope of the plots between points A and B indicated interactions to occur between 6 ED and anionic surfactants, The SDS concentration at the points A and B was less than that of 11 C-4. Interactions of the 6 ED/SDS system were found to occur more easily than those of the 6 ED/11 C-4 system.A flat portion was observed on the surface tension curve in the 6 ED/11 C-4 mixed system, and in this portion, a mixed micelle was noted to be formed. The surface tension was found to decrease when the concentration of 6 ED was made high. In contrast, the absorbance of I-3 increased regularly, due to interaction of the 6 ED micelle with I-3, owing to the presence of 6 ED in excess. By the present I-3 solubilization method, some single 6 ED micelles and 6 ED rich mixed micelles were confirmed to be formed in the higher concentration region of 6 ED.