BUTTERFLY PATTERNS IN A SHEARED LAMELLAR SYSTEM

We studied the influence of shear on a lyotropic lamellar phase using the ILL Couette type shear cell on the SANS spectrometer D11 at the IL L, Grenoble. Because of the broad range of momentum transfers availabl e on this instrument a characteristic butterfly pattern with a scatter ing peak along the neutral direction revealing both the structure and the supramolecular structure of the system could be detected at very h igh shear rates and very low Q. After cessation of flow the butterfly pattern disappeared immediately and the diffraction pattern showed a r ing with an intensity maximum still perpendicular to the direction of how. We present a model in real space describing this new structure of a lamellar phase at high shear rates. (C) 1998 Elsevier Science B.V. All rights reserved.