A lamellar poly(styrene-b-isoprene) diblock copolymer is well-aligned,
as observed by TEM and SAXS, by continous, nonlinear oscillatory shea
ring, at a surprisingly low strain amplitude, specifically 5 %, and a
temperature 20-degrees-C above the glass transition temperature of the
PS block. This aligned state exhibits lamellae parallel to the sample
plane, that is, with the normal of the lamellae parallel to the shear
gradient. The onset of nonlinear viscoelastic effects occurs at small
strains, approximately 1 %. Oscillatory shear within the linear regim
e does not effectively align the block copolymer morphology. Steady sh
ear disrupts well-aligned samples by introducing defects, namely wall
and focal conic defects. We distinguish between intermediate and globa
l length scales of alignment using TEM and SAXS, respectively. Althoug
h significant morphological differences exist between the various samp
les, the dynamic mechanical responses of these copolymer samples are i
ndistinguishable over the frequency range examined. Our experimental r
esults are inconsistent with the proposed grain rotation mechanism as
the sole mechanism of alignment of block copolymer; a destruction/refo
rmation mechanism is necessary to explain the transformation of the in
itial morphology to having global alignment.