Influence of the chemical nature of various geometries on the rheological behavior of a lamellar lyotropic phase

The influence of the chemical nature of the substrate was studied in order to determine its impact on the rheological behavior of lyotropic lamellar p hases. Small-angle x-ray diffraction analysis established that the plastic behavior of the samples could be explained by the large disorganization of the lamellar layers in the vicinity of surfaces as stainless steel, gold, t in, copper, and bismuth. On the other hand, layer alignment was almost perf ect on quartz, and the lamellar samples displayed a dominant viscous behavi or induced by the flow of the lamellar layers in the vicinity of the surfac es. On zinc sulfide, an in between behavior was observed and the lamellar s ample showed two yield stress. one is necessary to induce local alignment o f layers in the vicinity of the surfaces, and the other must align the laye rs of the lamellar sandwich in the flow direction. Assumptions as to the or igin of the complex and varied organization have been studied by considerin g the surface free energy and the surface topology. However, no obvious rel ationship could be established between surface free energy and liquid cryst al alignment. Similarly, no influence of the topology on lamellar orientati on could be brought to the fore. (C) 1999 The Society of Rheology. [S0148-6 055(99)00804-4].