The influence of shear on lyotropic lamellar phases in the system sodium dodecyl sulfate (SDS)/decanol/water has been studied using small angle neutron and light scattering (SANS, SALS), birefringence and rheology. Eight different samples with a constant water content of 67.4%, but different surfactant-cosurfactant ratio were studied. Static SANS measurements showed that replacing of SDS with decanol leads to a transition from a defective lamellar phase, characterized first by a ribbon like structure and then by a pore like structure, to a classical lamellar phase. An orientation diagram was obtained from SANS, SALS and birefringence measurements under shear. For samples with low decanol content, shear flow leads to an alignment of lamellae but in addition to previous studies, we found two reorientations, from a parallel (at low shear rates) to a perpendicular alignment of the lamellae (with respect to the walls of the shear cell) and to a parallel alignment again at the highest shear rates available. At intermediate decanol content, a shear induced formation of multilamellar vesicles was observed in a certain shear rate region. Samples with classical lamellar structure at high decanol content exhibited no shear induced vesicle formation.

The shear-induced structure formation in lyotropic lamellar phases containing water-soluble polymers is investigated. The lyotropic phases consisted of sodium dodecyl sulfate/1-decanol/D2O and were mixed either with poly(n-isopropylacrylamide) (PNIPAM), hydroxyethyl starch (HES), poly(vinyl caprolactame) (PVCa), or poly(ethylenglycol)distearate (PEG-DS). Rheo-optical experiments (flow birefringence and small-angle light scattering, SALS) as well as small-angle neutron scattering (SANS) combined with a commercial rheometer were used to observe structural changes, e.g., layer reorientation or formation of multilamellar vesicles (liposomes). Equilibrium properties of the lamellar phases were investigated using quasi elastic light scattering (QELS) and static SANS, the latter was analyzed using a model proposed by Nallet et al. The polymer addition led to a viscosity increase but the flipping of aligned lamellae from parallel to perpendicular orientation was hardly affected by the polymers. The shear-induced formation of multilamellar vesicles (MLV), however, was strongly influenced by the macromolecules. The addition of small amounts of PNIPAM shifted the region where vesicles are formed to samples with higher decanol contents whereas HES, PVCa, and PEG-DS suppressed the MLV formation in all cases. Results from SANS and QELS indicate a possible correlation between the shear-induced vesicle formation and the viscoelastic properties of the surfactant bilayer.

The influence of shear on a defective lamellar phase of the ternary mixture sodium dodecyl sulphate/decanol/D2O was studied using small-angle neutron scattering (SANS), smallangle light scattering (SALS) and birefringence. Shear flow leads to an alignment of lamellae but in addition to previous studies, we found a reorientation from "perpendicular" lamellae, i.e. with the layer normal along the vorticity direction, to "parallel" lamellae with the layer normal along the velocity gradient direction at increasing shear rates. The reorientation processes were accompanied by a decrease of viscosity.