Physicochemical properties of the α,ω-type surfactant in aqueous solution

Abstract

The physicochemical properties of the α,ω-type surfactant (disodium dodecyl disulfate) in aqueous solution have been investigated by means of surface tension, conductivity, solubilization of various solubilizates, static light scattering, and 13 C NMR chemical shifts. The surface tension and conductivity measurements indicate the existence of two discontinuities which are referred to as the first CMC and the second CMC. The α,ω-type surfactant molecules change their conformation at an air-water interface and form a “wicket-like” conformation at the second CMC. By the static light scattering being measured the micellar aggregation number above the second CMC is determined to be 90 ± 5 (25°C). This value agrees fairly well with that obtained by 13 C NMR chemical shift data. The above results support the notion that between the first CMC and the second CMC the α,ω-type surfactant forms premicellar (several numbers of aggregates) and, above the second CMC, forms ordinary micelles which are very loosely aggregated.