Influence of water-soluble polymers on the shear-induced structure formation in lyotropic lamellar phases

The shear-induced structure formation in lyotropic lamellar phases containi ng water-soluble polymers is investigated. The lyotropic phases consisted o f sodium dodecyl sulfate/ 1-decanol/D2O and were mixed either with poly(n-i sopropylacrylamide) (PNIPAM), hydroxyethyl starch (HES), poly(vinyl caprola ctame) (PVCa), or poly(ethylenglycol)distearate (PEG-DS). Rheo-optical expe riments (flow birefringence and small-angle light scattering, SALS) as well as small-angle neutron scattering (SANS) combined with a commercial rheome ter were used to observe structural changes, e.g., layer reorientation or f ormation of multilamellar vesicles (liposomes). Equilibrium properties of t he lamellar phases were investigated using quasi elastic light scattering ( QELS) and static SANS, the latter was analyzed using a model proposed by Na llet et al. The polymer addition led to a viscosity increase but the flippi ng of aligned lamellae from parallel to perpendicular orientation was hardl y affected by the polymers. The shear-induced formation of multilamellar ve sicles (MLV), however, was strongly influenced by the macromolecules. The a ddition of small amounts of PNIPAM shifted the region where vesicles are fo rmed to samples with higher decanol contents whereas HES, PVCa, and PEG-DS suppressed the MLV formation in all cases. Results from SANS and QELS indic ate a possible correlation between the shear-induced vesicle formation and the viscoelastic properties of the surfactant bilayer.