Seeing mesoatomic distortions in softmatter crystals of a double-gyroid block copolymer

• Published in: Nature (London) Vol. 575; no. 7781; pp. 175 - 179O
• Main Authors: Feng, Xueyan, Burke, Christopher J, Zhuo, Mujin, Guo, Hua, Yang, Kaiqi, Reddy, Abhiram, Prasad, Ishan, Ho, Rong-Ming, Avgeropoulos, Apostolos, Grason, Gregory M, Thomas, Edwin L
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group 07.11.2019
• Subjects: Angles (geometry); Asymmetry; Block copolymers; Broken symmetry; Cell morphology; Copolymers; Crystal growth; Crystal lattices; Crystal structure; Crystals; Cytology; Fourier transforms; Ion beams; Mathematical morphology; Morphology; Multiscale analysis; Periodic structures; Qualitative analysis; Scanning electron microscopy; Symmetry; Thin films; Unit cell; Wave propagation
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/s41586-019-1706-1

Supramolecular soft crystals are periodic structures that are formed by the hierarchical assembly of complex constituents, and occur in a broad variety of 'softmatter' systems. Such soft crystals exhibit many of the basic features (such as threedimensional lattices and space groups) and properties (such as band structure and wave propagation) of their 'hard-matter' atomic solid counterparts, owing to the generic symmetry-based principles that underlie both. 'Mesoatomic' building blocks of soft-matter crystals consist of groups of molecules, whose sub-unit-cell configurations couple strongly to supra-unit-scale symmetry. As yet, high-fidelity experimental techniques for characterizing the detailed local structure of soft matter and, in particular, for quantifying the effects of multiscale reconfigurability are quite limited. Here, by applying slice-and-view microscopy to reconstruct the micrometre-scale domain morphology of a solution-cast block copolymer double gyroid over large specimen volumes, we unambiguously characterize its supra-unit and sub-unit cell morphology. Our multiscale analysis reveals a qualitative and underappreciated distinction between this double-gyroid soft crystal and hard crystals in terms of their structural relaxations in response to forces-namely a non-affine mode of sub-unit-cell symmetry breaking that is coherently maintained over large multicell dimensions. Subject to inevitable stresses during crystal growth, the relatively soft strut lengths and diameters of the double-gyroid network can easily accommodate deformation, while the angular geometry is stiff, maintaining local correlations even under strong symmetry-breaking distortions. These features contrast sharply with the rigid lengths and bendable angles of hard crystals.