Viscoelastic properties of aligned block copolymer lamellae

Structure-property relationships of aligned block copolymer lamellae in the vicinity of the order-disorder transition are studied by a combination of optical birefringence and rheology. Minimizing defect density was a crucial part of our experiments. The organization of block copolymer chains into aligned lamellae leads to a reduction in both zero shear viscosity and compliance relative to the disordered state. The frequency dependencies of the storage and loss shear moduli of the aligned lamellae are close to the Rouse prediction. In addition, the measured value of the compliance of the ordered and aligned state is within a factor of 2 of the Rouse prediction (agreement obtained with no adjustable parameters). In contrast, large differences between the experiments and the Rouse model are seen in the disordered state due to the presence of concentration fluctuations.