Shear alignment of sphere-morphology block copolymer thin films with viscous fluid flow.

The effect of shear on crystalline order is interesting fundamentally, as well as technologically, for producing long-range alignment of micron- and nanoscale structures. We study the influence of shear on a sphere-forming diblock copolymer thin film consisting of a stack of two to six hexagonal layers, using a stress-controlled rheometer to transmit the stress through a viscous fluid layer. Above a threshold stress, the hexagonal layers align macroscopically in the "easy shear" direction. A simple phenomenological model with an orientation-dependent order-disorder temperature, T*(ODT)(deltatheta)=T(ODT)[1-(sigma/sigma(c))sin2(3 deltatheta)] and recrystallization describes the influence of stress level, temperature, and shearing time remarkably well.