Directly Visualizing Conformations of Bottlebrush Polymers in Bulk Films using Super-Resolution Optical Microscopy

Bottlebrush polymers consist of a polymeric backbone densely grafted by side chains. Their elongated chain conformations drive many of their properties, so studying the relationship between molecular architecture and conformation is valuable to design materials for applications. So far, studies have investigated conformations for single chains on surfaces and in dilute solutions, but few studies have investigated conformations in bulk environments. Here, we visualize single bottlebrush chains in the bulk by mixing dilute quantities of dye-labeled bottlebrushes with unlabeled linear chains and imaging using super-resolution optical microscopy (SROM). SROM bypasses the diffraction limit by localizing dye molecules attached along a structure to provide high-resolution images. After imaging single chains, their rigidities were quantified using a persistence length determined by fitting the tangent correlation functions of the backbones to the worm-like chain model. Our analysis methods were verified by simulation. Conformations were studied with changes to side chain length (600-3500 g/mol), grafting density (8%, 40%, 100%), and background polymer molecular weight (2-350 kg/mol). We observe more rigid chains compared to bottlebrush studies in dilute solutions.