Time-resolved 2d-SAXS measurements to reveal mechanism of cylinder orientation upon sphere-to-cylinder transition under a planar flow in an SEBS triblock copolymer sheet

Abstract

We report experimental results of time-resolved 2d-SAXS measurements for a polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene (SEBS) triblock copolymer as-cast film, which was subjected to a planar flow gradually imposed in the heating process of the specimen at a ramp-up rate of 2°C/min. Before heating, non-equilibrium spheres were formed in the specimen. At 144°C, the spheres were found to completely transform into cylinders. Some extent of cylinder orientation (0.5 in orientation factor) was already achieved, even at that temperature the strain of the specimen was as low as 0.5. From this fact, the directional coalescence of non-equilibrium spheres along with the planar flow direction (FD) was implied. As temperature increased, it was found the progress of the cylinder orientation parallel to FD as well as the orientation of the (101¯0) planes of hexagonal lattice parallel to the substrate surface. The fraction of the peak-top intensities of the (112¯0) reflections, I(112¯0)/(I(101¯0)+I(112¯0)), was evaluated to examine the change in the orientational state of hexagonal lattice during application of the planar flow. The fraction was found to moderately increase with strain. However, the fraction of the grains, in which the (101¯0) planes are parallel to the specimen surface, is as low as 0.07 even at the highest strain state.