Morphological evolution of oriented clay-containing block copolymer nanocomposites under elongational flow

We have studied the effects of elongational flow on the morphology of nanocomposites of polystyrene-b-poly(ethylene-co-butylene)-b-styrene (SEBS) triblock copolymers – with aligned cylindrical morphologies – containing organoclays. These nanocomposites were elongated along two perpendicular directions at varied Hencky strain rates. Small angle X-ray scattering measurements indicate that the different types of deformation induce very different microstructural changes during the elongation processes. When elongated along the direction parallel to the extrusion direction, pure copolymers under low strain rates exhibit an increasing alignment of the cylinder axes while under high strain rates a disorientation effect prevails. When elongated at low strain rates along the transversal direction, the axes of the cylinders rotate an angle close to 90°, thus becoming parallel to the elongation direction, while under high strain rates the rotation is incomplete. The addition of clay causes different effects on the final morphology after elongation depending on the sizes and degree of clay dispersion and on the predominant interactions between clay and copolymer domains.