Kinetic Pathway of the Order-Order Transition from Hexagonally Packed Cylinder to Hexagonally Perforated Layer in Polystyrene-block-Poly(2-vinylpyridine) Using Time-Resolved 3D Transmission Electron Microtomography

The kinetic pathway of the order-order transition (OOT) from a hexagonally packed cylinder (HEX) to a hexagonally perforated layer (HPL) phase in polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) was studied using time-resolved three-dimensional transmission electron microtomography (3D-TEM). Our results revealed that this OOT proceeds via the nucleation and growth process. During the nucleation stage, the cylindrical domains transition from an initial metastable state at random positions owing to thermal fluctuation. Adjacent undulating cylindrical domains merge into wave-like structures to form perforations in hexagonal packing and act as nuclei. During the growth stage, after each nucleus exceeds the critical size, the neighboring intermediates coalesce into the HPL phase with AB-type stacking (P6₃/mmc space group). The coherency of the HPL orientation in the grain increased during OOT. Understanding the OOT kinetic pathway is useful for the morphological evolution of block copolymers and for designing suitable transition pathways to obtain ordered structures for diverse nanotechnology applications.