| Numerous macromolecular systems including concentrated surfactant solutions, block copolymers and biomembranes form a "lamellar phase" where rodlike molecules arrange themselves in parallel layers. Application of external forces or confinement distorts the layer structure, leading to the formation of micron scale topological defects. These defects interact with and dramatically alter the macroscopic flow.;Our measurements indicate that application of shear flow to defect filled samples leads to strain induced structural transitions and an increase in texture ordering leading to defect self assembly.;In this work we study this complex interaction using a custom-built shear cell and real time texture visualization. We study the formation and ordering of the defect textures and describe important features of the growth of layer instabilities leading to defect formation. We subject the defects to well controlled flow situations, and report the modification of the velocity profile due to the presence of these defects and due to their interaction with dislocations. We establish that the low frequency motion is dictated by interaction with dislocations, consistent with previous viscosity measurements. At long times, the defect textures change due to flow and we identify the important mechanisms in the evolution of the defect texture with time. We observe an exponential decay of defect intensities and propose a scaling argument to explain this decay. Finally, we study the effect of shear flow on surface anchored defects, and characterize important lengthscales and timescales involved in structural changes arising out of the interaction of shear flow and layer elasticity. |
