Sphere morphology of block copolymer systems under shear

The existence of a stable periodic time-dependent solution of Landau-Ginzburg–type dynamics of a sheared system is first shown by the simulations. By means of density-functional simulations we have shown that a spherical micellar phase of block copolymers is not destroyed by shear below a certain level, but forms elongated droplets instead. We found similar results for the BCC phase in several systems: diblock copolymer melts and a triblock ABA-copolymer/solvent mixture. At shear rates above the critical value, the spherical phase transforms into a hexagonal cylindrical phase. After cessation of shear, the cylindrical phase breaks up into an oriented monocluster of a spherical BCC phase, in agreement with the interpretation of experiments by Koppi et al. ( J. Rheol., 38 (1994) 999).