Rheo-small-Angle-Light-Scattering Investigation of Shear-Induced Structural Changes in a Lyotropic Lamellar Phase
✍ Scribed by Jörg Läuger; Richard Weigel; Klaus Berger; Karl Hiltrop; Walter Richtering
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 421 KB
- Volume
- 181
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
when a cosurfactant is added and, e.g., nematic phases can The influence of shear on a lamellar phase in the system sodium then be observed (5-7).
dodecyl sulfate/decanol/water was investigated by combined rheo-Samples of macroscopic size are not homogeneously small angle light scattering. Three different regions were detected aligned, but usually a polydomain structure characterized by and all could be characterized by different scattering patterns in a nonuniform director orientation is observed. Shear flow depolarized and polarized light scattering. Flow alignment of anihas a profound effect on the structure and macroscopic alignsotropic domains in flow direction was found at low and high ment of liquid crystals, and consequently the rheological shear rates. A viscosity maximum was observed at intermediate properties of such materials are rather complex. Some studshear rates, and different anisotropic scattering patterns were deies on these rheological properties of lyotropic mesophases tected in polarized and depolarized scattering. The data are interpreted by a shear-induced formation of vesicles which displayed have been performed during the past years and have always a characteristic four-lobe pattern in depolarized scattering. A butreported complicated behavior (8-18). Since mechanical terfly pattern observed in polarized scattering indicated the exisdeformations can alter the structure, it is necessary to monitence of concentration fluctuations along the flow direction. The tor the structural changes during shear flow, to further undertransitions between the three regions were reversible, but the forstand the rheological properties of complex fluids. Different mation of vesicles was found only when the sample was sheared rheo-optical techniques such as small angle light scattering for a long time at appropriate shear rates. Complicated rheological (SALS) and small angle neutron scattering (SANS) or flow properties as, e.g., shear thinning and shear thickening, were found birefringence have been developed to study flow-induced as a consequence of the structural changes.