Lamellar Orientation and Corresponding Rheological Properties of Symmetric Diblock Copolymers under Steady Shear Flow

ABSTRACT: The kinetics of lamellar orientation and rheological properties of symmetric diblock copolymers under steady shear flow using the time-dependent Ginzburg-Landau (TDGL) approach were studied. The simulation results show that a high shear rate can induce a perpendicular alignment for temperatures just below the order-disorder transition (ODT). On the other hand, a low shear rate induces initially mixed morphologies composed primarily of perpendicular and parallel orientations; eventually, the perpendicular alignment is transformed into a parallel alignment via undulation instability. On the contrary, with decreasing temperature, the high shear rate produces a parallel alignment, and the low shear rate induces a perpendicular alignment. The results also show that the reduced shear viscosity rapidly reaches a maximum at a reduced shear strain near one and then decreases. The first and second normal stress differences N1 and N2 are related to the lamellar alignment. 1