Influence of sodium dodecyl sulfate on structure and rheology of aqueous solutions of the nonionic surfactant tetraethyleneglycol-monododecyl ether (C12E4)

The influence of the ionic surfactant sodium dodecylsulfate (SDS) on structure and theology of the lamellar phase of the nonionic surfactant tetraethyleneglycol-monododecyl ether (C12E4) at intermediate concentrations was investigated by means of small angle light and neutron scattering (SALS, SANS) and rheometry. The long range orientational order increased with added SDS as expected and the Caille parameter was obtained from SANS data. The shear viscosity increased when SDS was added. Rheo SALS experiments revealed the shear induced formation of multilamellar vesicles (MLV or 'onions') and the MLV size decreased not only in shear thinning but also in the shear thickening region. The increase in Bragg scattering intensity along the flow direction as observed in the rheo-SANS experiments also revealed the increase in MLV volume fraction in the shear thickening regime. The SANS data further showed a decrease in layer spacing with increasing shear which indicates that water is squeezed out of the vesicles. (C) 2001 Elsevier Science B.V. All rights reserved.