Coalescence of non-equilibrium spheres through thermal annealing in a polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene triblock copolymer film under a uniaxially stretched state

We report the experimental results of an attempt to control the orientation of cylindrical microdomains using the directional coalescence of non-equilibrium spheres along the stretching direction (SD) of a triblock copolymer film. Thermal annealing, which induced the sphere-to-cylinder transition, was performed on the triblock copolymer film under the uniaxially stretched state. The orientational state of the body-centered cubic (BCC) lattice composed of spheres and a hexagonal lattice of cylinders were analyzed via atomic force microscopy and in situ two-dimensional small-angle X-ray scattering (2d-SAXS) measurements. Unlike the application of shear flow, cylinder orientation with its long axis parallel to the SD was not achieved by uniaxial stretching. The 2d-SAXS pattern for the specimen under the uniaxially stretched state showed a four-streak pattern, which quickly became more evident following thermal annealing and then changed into a four-spot pattern just before the sphere-to-cylinder transformation. The fact that the four-spot pattern is stable prior to the transformation suggests lattice commensuration upon the transformation from the deformed BCC lattice to the undeformed lattice without large-scale rearrangement of the spheres.