Revealing the 3D Structure of Block Copolymers with Electron Microscopy: Current Status and Future Directions

Block copolymers (BCPs) are consideredmodel systems for understandingand utilizing self-assembly in soft matter. Their tunable nanometricstructure and composition enable comprehensive studies of self-assemblyprocesses as well as make them relevant materials in diverse applications.A key step in developing and controlling BCP nanostructures is a fullunderstanding of their three-dimensional (3D) structure and how thisstructure is affected by the BCP chemistry, confinement, boundaryconditions, and the self-assembly evolution and dynamics. Electronmicroscopy (EM) is a leading method in BCP 3D characterization owingto its high resolution in imaging nanosized structures. Here we discussthe two main 3D EM methods: namely, transmission EM tomography andslice and view scanning EM tomography. We present each method'sprinciples, examine their strengths and weaknesses, and discuss waysresearchers have devised to overcome some of the challenges in BCP3D characterization with EM- from specimen preparation to imagingradiation-sensitive materials. Importantly, we review current andnew cutting-edge EM methods such as direct electron detectors, energydispersive X-ray spectroscopy of soft matter, high temporal rate imaging,and single-particle analysis that have great potential for expandingthe BCP understanding through EM in the future.

Automated summary

BCP is a model system for studying and utilizing self-assembly in soft matter. Electron microscopy is a leading method for characterizing the three-dimensional structure of BCPs. This article discusses the principles, strengths, weaknesses, and challenges of two main 3D EM methods: transmission EM tomography and slice and view scanning EM tomography. It also reviews current and new cutting-edge EM methods that have the potential to expand our understanding of BCPs in the future.