Transient viscoelastic properties of lamellae-forming diblock copolymers with flow-induced alignment

The transient viscoelastic properties of lamellae-forming poly(styrene-block-2-vinylpyridine) and poly(styrene-d₈-block-2-vinylpyridine) were measured to examine the alignment process of lamellae. Rescaled transient stress σ(t) after step increase of shear rate could not be scaled by strain or time, and the data showed poor reproducibility. σ(t) upon the onset of flow after a given rest time showed relatively large overshoot, while it instantaneously became steady upon the reverse of flow. These results suggest that the average degree of alignment is the same at the steady states, but the transient stresses are determined by the size and number of grains that undergo alignment.