A transition from shear-induced order to shear-induced disorder in block copolymers

The effect of steady shear flow on a weakly ordered block copolymer material was examined by in situ small angle neutron scattering. We demonstrate this material undergoes a transition from shear-induced ordering to shear-induced disordering at a fixed temperature above the quiescent disordering temperature. Current theories, which assume that the primary effect of shear flow on block copolymers is to suppress disordered concentration fluctuations, can only predict shear-induced ordering. Our results indicate that the coupling between flow and microstructure is not unique and that it can change qualitatively with shear rate. (C) 1996 American Institute of Physics.