Investigation of shear-induced structures in lyotropic mesophases by scattering experiments

Abstract

The influence of shear on the structure of lyotropic liquid crystalline phases was investigated by small angle light and neutron scattering (SALS, SANS). Three different systems were studied involving nonionic and ionic surfactants: a hexagonal phase, a lamellar phase and a defective lamellar phase. Three different regimes are discussed in the hexagonal phase. A polydomain sample with dominating elastic properties, an aligned sample with the rodlike micelles being aligned in flow direction and characterized by a stripe texture. This texture can be disrupted at high shear rates leading to a further decrease of the moduli. Different regimes were also found with the defective lamellar phase. Multilamellar vesicles were formed at intermediate shear rates leading to an increase of viscosity. At higher shear rates these vesicles were destroyed and oriented lamellae were obtained. The lamellae were aligned with the layer normal parallel to the neutral (vorticity) axis. Vesicles were also obtained with a classical lamellar phase. Here the vesicles could not be destroyed at high shear rates but a butterfly pattern was observed in light and neutron scattering.