Investigation of Bottlebrush Polymer Chain Conformations under Mechanical Deformation using Super-Resolution Optical Microscopy

Understanding polymer behavior under mechanical deformation is a fundamentally important topic in polymer physics. Despite significant modeling, simulation, and experimental effort, studies at the molecular level are still challenging to perform, especially for real-time characterization of chain conformations. In this work, we directly visualized bottlebrush polymers in a thin film using super-resolution optical microscopy (SROM), as they were compressed under a spherical piezoelectric-controlled indenter. The film consists of poly(n-butyl acrylate) bottlebrushes where a small portion was labeled by a photoswitchable dye. Using SROM, we were able to observe and quantitatively describe the change in the orientation of the bottlebrush chains in the strain field during spherical indentation. We then solved the strain field by finite-element simulation and correlated the experimental and theoretical results. Our study provides a single-molecule description of polymer chain behavior within a solid material under deformation, which contributes to establishing the correlation between the unique macroscale mechanical properties of bottlebrush elastomers and microscale molecular motion.