Organic solution-phase transmission electron microscopy of copolymer nanoassembly morphology and dynamics

Abstract

Direct imaging of the dynamics of polymeric assemblies in organic solvents is an outstanding challenge. Herein, we apply liquid cell transmission electron microscopy (LCTEM) to study polymeric nanomaterials in organic solvents. LCTEM is distinct from other TEM methods as it can be applied to characterize the morphology of nanomaterials in organic solvents. To enable this demonstration, we examined electron-solvent interactions for two common organic solvents, N,N-dimethylformamide and methanol, and compared these solvents to water. For each solvent, we developed Monte Carlo simulations and kinetic radiolysis models, providing scattering and chemical insight, respectively. Guided by theoretical results, we applied LCTEM and postmortem mass spectral imaging of poly(styrene)-b-poly(4-vinylpyridine) assemblies in each solvent. Then, a worm-to-micelle transformation in poly(styrene)-b-poly(4-vinylpyridine) was triggered via organic solvent mixing during LCTEM, enabling an experiment not possible through a cryogenic TEM time series. Our work provides a pathway for an expanded examination of nanomaterials in organic solvents via LCTEM, a neglected research area despite the obvious prevalence of such materials across chemistry and materials science.