No abstract

Shear-induced alignment of phase-separated domains in a triblock copolymer has been studied by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). The material used was triblock Copolymer styrenebutadiene-styrene with a phase-separated morphology of hexagonally packed cylinders of poly(styrene) in a poly(butadiene) matrix. We started with an ordered structure, where the cylinders were aligned with a common director throughout the sample, and imposed a well-defined shear flow perpendicular to this director. Shear flow rotated the cylinder orientation by 90° into the shear direction. At all observed strains, the hexagonal faces preferred to orient parallel to the shear plane. To produce the initial order, a solution-cast film was subjected to planar extension, aligning the cylinders in the extension direction. With a novel sample preparation technique, we were able to transform this rectangular sample into an axisymmetric geometry needed for large shear strain i s a rotational rheometer with parallel disk fixtures. SAXS and TEM were used to observe shear-induced orientation transitions as a function of applied strain on room-temperature-quenched samples. We observed intermediate textures at small strains, maximum alignment at intermediate strains, and deterioration of order at large strains. By following the transitions from one aligned Structure to another, we discuss the processee that produce domain orientation under shear flow.

No abstract