Physicochemical Properties of α,ω-Type Surfactant in Aqueous Solution. Bis(triethylammonium) 1,20-Eicosanediyl Disulfate

Abstract The physicochemical properties of the α,ω-type (bolaform) surfactant, bis(triethylammonium) 1,20-eicosanediyl disulfate (α,ω C20N2Et6), in aqueous solution have been investigated by means of surface tension, electrical conductivity, dye solubilization and time-resolved fluorescence quenching. The critical micelle concentration of α,ω C20N2Et6 was 1–1.3×10−3 mol dm−3. The micelle ionization degree of the surfactant was larger than a conventional surfactant having the same head group. From surface tension measurements, the molecular area of α,ω C20N2Et6 at the air–water interface was found to be about twice as large as that of a normal type surfactant, such as sodium dodecyl sulfate (SDS). This reveals that α,ω C20N2Et6 probably forms vertical looping (“wicket-like” conformation) at the air–water interface. By time-resolved fluorescence quenching measurements, the aggregation number of α,ω C20N2Et6 micelle was found to be strongly dependent on the concentration, but only slightly dependent on the temperature. At low concentrations the aggregation number is close to half that corresponding to a normal type surfactant having a chain length that is that of the bolaform. The solubilizing power of a micellar solution of α,ω C20N2Et6 toward Orange OT was 7.6×10−3 mol of dye per mol of surfactant, that is, a value smaller than that of SDS.