Flow behavior and impact of shear fields on structural transitions in diblock and triblock copolymer aqueous solutions

Low molecular weight diblock and triblock polymers in selective solvents form disordered micellar phases at low concentration and liquid crystal phases at high concentration (or low solvent to amphiphile molar ratio in the case of water). The energetic barriers between different lyotropic states and structures are large enough for systems to become kinetically trapped, but low enough for weak external fields to alter the nanoscale structure. We have been able to align ordered structures and anneal out defect texture in polycrystalline materials. Results for two different block copolymers in aqueous solution will be shown and rheological features correlated with structural measurements (through SANS and SAXS). The use of weak shear fields to align lyotropic structures and then transition to other low and high symmetry structures will be demonstrated.