Designing conformationally dynamic molecules that self-assemble into predictable nanostructures remains an important unmet challenge. This paper describes how atomic-scale cryogenic transmission electron microscopy (cryo-TEM) can be used to explore the relationship between molecular structure and self-assembly of block copolymers. We examined sheetlike micelles formed in water using a series of diblock copolypeptoids with the same hydrophilic block and three distinct crystalline hydrophobic blocks. Our cryo-TEM images revealed all the structures share nansoscale features, but differ in their intermolecular packing geometries. Different molecular arrangements, parallel and antiparallel V-shaped crystal motifs, were revealed by two-dimensional atomic-scale through-plane images. However, images from tilted samples revealed an unexpected feature when the hydrophobic polypeptoid block comprised phenyl rings with substituted bromine atoms at the para position. The nanosheets contained atomic-scale corrugations that were absent in the other systems which comprised unsubstituted aliphatic and aromatic side chains. We hypothesize that these corrugations are due to the dipolar characteristics of the brominated phenyl group and interactions between this group and water molecules.

• Received 30 September 2023
• Accepted 8 January 2024

DOI:https://doi.org/10.1103/PhysRevMaterials.8.020301

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

This article appears in the following collection:

Self-Assembly of Complex Phases in Block Copolymer Materials

The Editors of Physical Review Materials are pleased to present the Collection on Self-Assembly of Complex Phases in Block Copolymer Materials, highlighting one of the most exciting fields in polymer science. Block copolymers offer an excellent model system for comprehending symmetry breaking in soft matter, as well as a unique platform for designing nanostructured materials. This Collection is being guest-edited by Kevin Dorfman from the University of Minnesota and Chris Bates from the University of California - Santa Barbara.