The micelles and their dynamic properties in the mixed surfactant systems; lithium perfluorooctanesulfonate/hexaoxyethylene glycol dodecyl ether (C 12E 6) and lithium dodecyl sulfate/C 12E 6

Abstract

In the mixed surfactant solutions lithium perfluorooctanesulfonate (LiFOS)/hexaoxyethylene glycol dodecyl ether (C 12E 6) and lithium dodecyl sulfate (LiDS)/C 12E 6, the micellar size and charge were estimated using electric birefringence, interfacial tension, viscosity, dynamic light scattering, and electric conductivity measurements. All measurements were carried out by varying the molar ratio of the two components at constant total surfactant concentration of 100 mmol/dm 3. Changes of micellar shape and size for the two systems show similarities to trends. The length of the mixed rodlike micelles increases with mole fraction of ionic surfactant, reaches a maximum, and then decreases. The maximum of the rod length with the mole fraction of the anionic surfactant is reflected in a maximum of the zero shear viscosity, the Kerr constant, the birefringence build up and decay time, and a minimum of the interfacial tension of the micellar solution against decane. This maximum length appears larger for LiFOS C 12 E 6 than for LiDS C 12 E 6 micelles. Binding of counterions in LiFOS C 12 E 6 system starts at the maximum length mole fraction, while for the LiDS C 12 E 6 system it starts at the rod-to-sphere transition point. These properties are explained by consideration of an effective packing ratio.