Edwin L. (Ned) Thomas, professor of materials science and engineering, Texas A&M University
"3D Structure of Grain Boundaries in Periodic Block Copolymer Tubular Networks"
Periodic tubular network materials such as the double gyroid and double diamond have many interesting properties due to their space group symmetries (band gaps and topologically protected modes) as well as superior charge and/or mass transport along with outstanding mechanical properties arising from their multi-channel triply continuous morphology. Of significant interest is the connectivity across grain boundaries in such materials. This talk will address sharp, coherent twin boundaries in a polystyrene-polydimethyl siloxane block copolymer which can form the double gyroid and double diamond structures. In addition, we also find thin aperiodic regions between grains that maybe be remnants of the precursor disordered states. The 3D structures are directly visualized using dual beam scanning microscopy. The tomographic reconstructions clearly show that the intermaterial dividing surface (IMDS) is smooth and continuous across the twin boundary planes. For the double gyroid, the (422) twin changes the handedness of the pairs of chiral PDMS networks, thus the boundary plane acts as a topological mirror. In the double diamond structure, the twin boundaries are (222) planes.