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 struct ure and theology of the lamellar phase of the nonionic surfactant tetraethy leneglycol-monododecyl ether (C12E4) at intermediate concentrations was inv estigated 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 shea r viscosity increased when SDS was added. Rheo SALS experiments revealed th e shear induced formation of multilamellar vesicles (MLV or 'onions') and t he MLV size decreased not only in shear thinning but also in the shear thic kening region. The increase in Bragg scattering intensity along the flow di rection as observed in the rheo-SANS experiments also revealed the increase in MLV volume fraction in the shear thickening regime. The SANS data furth er 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.