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.