3D Structure of Grain Boundaries in Tubular Network Block Copolymers

Multi-continuous microphases (such as double gyroid) have network structures with 3D interconnected, self supporting domains. The properties of the component in each domain are strongly expressed due to the geometrical continuity in all three dimensions. However, the occurrence of grain boundaries (GB), which interrupt the topological and geometrical order of the continuous ordered networks, will significantly affect their performance. Here, we examine GBs in a polystyrene-b-polydimethylsiloxane double gyroid system using high fidelity 3D reconstructions made by Slice and View scanning electron microscopy (SVSEM). Since large amounts of GB can be reconstructed, we employ machine learning to extract the shape/distribution of the GB. Also, two types of GBs are identified and described (grain-grain tilt and order-disorder-order boundaries). Different types of irregular nodes/topological loops/network connections within the GB region are identified. The local topological parameters, as well as curvature of the intermaterial dividing surface, node functionality distribution, strut length/orientation distribution and surface to volume ratio in the GB are analyzed and compared with the same set of morphological descriptors measured in the adjacent, ordered double gyroid grains.