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 ma terial was examined by in situ small angle neutron scattering. We demo nstrate this material undergoes a transition from shear-induced orderi ng to shear-induced disordering at a fixed temperature above the quies cent disordering temperature. Current theories, which assume that the primary effect of shear flow on block copolymers is to suppress disord ered concentration fluctuations, can only predict shear-induced orderi ng. Our results indicate that the coupling between flow and microstruc ture is not unique and that it can change qualitatively with shear rat e. (C) 1996 American Institute of Physics.