SHEAR-INDUCED TRANSFORMATIONS IN THE LAMELLAR PHASE OF HEXAETHYLENE GLYCOL MONOHEXADECYL ETHER

The shear-induced ordering of the lamellar phase of hexaethylene glyco l monohexadecyl ether, C(16)E(6), in a Couette shear cell has been obs erved by small angle neutron scattering, SANS, Two distinct lamellae o rientations have been identified, At low shear gradients the lamellae are ordered parallel to the flow-vorticity plane, whereas at higher sh ear gradients the lamellae order parallel to the flow-shear gradient p lane corresponding to a rotation through 90 degrees of the axis of ori entation. At shear gradients intermediate to those two extremes both o rientations are observed simultaneously, this being the first report o f such a morphology. A novel extension of shear alignment reported her e is the application of oscillatory Couette flow. Here, orientation pa rallel to the flow-vorticity plane and the intermediate state correspo nding to components oriented in the two orthogonal directions are obse rved. These observations are discussed in the context of recent result s of shear-induced effects observed in related systems. The additional information obtained from shear flow alignment and from measurements where the neutron beam is incident in a direction orthogonal to the sh ear gradient (cell side) and parallel to the flow direction has enable d a re-evaluation of the nature of the ''defective'' lamellar phase.