Reticulation of Block Copolymer Nanostructures from Perforation

This work aims to examine a variety of metastable phases from the controlled self-assembly of a lamellae-forming polystyrene-<i>block</i>-polydimethylsiloxane (PS-<i>b</i>-PDMS) and its blends with a PDMS homopolymer. Kinetically trapped phases including hexagonally perforated lamellae (HPL), double diamond (DD), and double gyroid (DG) can be obtained from the blends, making it feasible to investigate the transition mechanisms from perforation to reticulation for the formation of network phases (i.e., DD and DG) as evidenced by temperature-resolved small-angle X-ray scattering experiments. Most interestingly, on the basis of the 3D reconstruction of transmission electron microscopy (TEM) images (electron tomography), an epitaxial relationship between the [001] direction of HPL and the [111] direction for DG and DD phases for the transformations from HPL to DG and DD, respectively, can be clearly identified. Specifically, the 3D double networks of PDMS are initiated from the parallel PDMS layers with PS perforation, forming the topological building units for the gyroid (trigonal planar texture) and diamond (tetrapod texture) phases. As a result, this finding may fill up the lost parts of the morphological evolution from perforation to reticulation in terms of topological transformations.