Solubilization Behavior of the Surfactant–Polyethylene Glycol Complex in Relation to the Degree of Polymerization

Abstract

Abstract The solubilization behavior of the complexes composed of a surfactant and polyethylene glycol (PEG) toward an oil-soluble dye, Yellow OB, has been studied in relation to the degree of polymerization, n, of PEG. The solubilizing powers of the anionic surfactants, sodium dodecyl sulfate and sodium p-octylbenzene sulfonate, become greater on the addition of PEG, the extent depending on n. They increase as n increases. It is proposed that there are at least two different types of complexes, i.e., “oligomeric” and “polymeric” PEG–surfactant complexes. The boundary between the oligomeric and polymeric PEG’s is estimated to be around an n value of 10–15. With an oligomeric PEG–surfactant complex, the solubilization of Yellow OB would occur mainly in the hydrocarbon part of the surfactant micelle. With a polymeric PEG–surfactant complex, on the other hand, the solubilization would take place in the region of a complex rich in PEG. Electrical-conductivity and absorption-spectral data on the complexes are also included in this paper.