Fluctuations with cubic symmetry in a hexagonal copolymer microstructure

A triblock copolymer that undergoes a thermotropic order-order transition b etween hexagonally packed cylinders (C) and body-centered-cubic spheres (S) is examined. Transmission electron microscopy provides real space images, and small-angle x-ray scattering the reciprocal space signature, of fluctua tions with cubic symmetry in the stable (shear-aligned) hexagonal phase. Th ese results support recent theoretical predictions. There is evidence of an interesting induction time for the onset of fluctuations that is attribute d to a slight mismatch in principal lattice spacings between the C and S mi crostructures.