Shear alignment of spherical microdomain block copolymer thin films via a viscous fluid layer.

Shearing block copolymer thin films has recently been shown to be a simple method to produce macroscopic orientation and order of the microdomain patterns. We study the alignment of thin films (two or three layers) of a sphere-forming polystyrene-\emph{b}-poly(ethylene-\emph{alt}-propylene) polymer under steady shear flows. With the diblock film as the bottom plate of a rotating plate-plate rheometer and PDMS oil to transmit the shear viscously while annealing above the glass transition and below the order-disorder temperatures, we produce long range order without applying a normal force. This geometry also allows the evaluation of the alignment as a function of stress on a single sample. We observe a temperature-dependent threshold stress for alignment, and propose a possible mechanism for alignment of spheres.