ANOMALOUS RHEOLOGICAL BEHAVIOR OF ORDERED PHASES OF BLOCK-COPOLYMERS .1.

Computer simulation is carried out for microphase-separated diblock co polymers under applied shear deformation. A mesophase of hexagonally o rdered cylindrical domains is considered, and shear strains are applie d perpendicular to the cylinder axes. Rheological responses and struct ural changes of the system under oscillatory and step-shear strains ar e studied by,using a cell dynamic approach. For small strains, the usu al behavior of ordered viscoelastic solids is seen, while for large st rains, anomalous behavior is observed, including (i) in the case of os cillatory shears, a nonlinear stress response which is out of phase wi th the applied strain in the low frequency limit and (ii) in the case of step-shear, a double stress relaxation process in which the stress first approaches a pseudoequilibrium value and then much later relaxes further toward the final equilibrium value. This anomalous behavior i s shown to be due to the slippage of lattice planes.