Visualization of polymer conformations under mechanical deformation using super-resolution optical microscopy

The investigation of polymer structures and dynamics is of considerable importance for polymer physics. However, obtaining single-chain level insights, especially with real-time and real-space characterization, has been a long-standing challenge. Addressing this, super-resolution optical microscopy (SROM) has been identified as an effective tool for non-invasively imaging individual polymer chains in bulk environments, thereby enabling the direct observation of how chains respond to mechanical deformation. In our study, we used spherical indentation as a method to exert external force, and we applied SROM to directly visualize the behavior of bottlebrush poly(n-butyl acrylate) chains in a thin film under the indentation. We were then able to quantitatively describe the change of chain conformations in the contact area under varied conditions. To experimentally determine this displacement field and provide a theoretical prediction of the polymer chain behavior, we tracked fiducial marks in the film under identical indenting conditions, then confirmed these findings through finite element analysis. Our study stands as a pioneering effort in visualizing real-time polymer conformational shifts in bulk, providing transformative insights into polymer behavior and dynamics.