Osmometric study of commercial surfactants

The micellar weights of Tergitol 15-S-9 (Union Carbide) and of Neodol 25-9 (Shell Chemical Co.) were determined by membrane osmometry in water as 98,000 and 82,000, respectively (36.5 C). Both surfactants contained a small amount of a nonassociating component. The micelles were found to be extremely stable. The micellar weight of Aerosol OT (American Cyanamid) was determined as <5,900 (toluene, 34 C). The results of this investigation indicate the usefulness of membrane osmometry in the determination of micellar weights of surfactants. Information with respect to the stability of the micelles and the dialytic behavior of surfactants in general can be obtained from the osmotic pressure-time curve.