The conformation of polymer chains can dictate material properties and are usually determined by scattering-based techniques. While effective, they can only provide information in reciprocal space, which requires accurate model selection for data fitting. To complement with these characterization methods, this work develops a fluorescence-based approach to determine the end-to-end distances of polymer chains in real-space using Förster resonance energy transfer (FRET). FRET is a method that has been often used in the field of biology for measuring the distance between two species at a nanometer length scale through determining the energy transfer efficiency between a donor fluorophore and an acceptor molecule that are in close proximity. However, its efficient use in polymer science is still in infancy. By labeling donor and acceptor molecules on different polymer chain ends respectively, FRET enables direct measurement of the averaged polymer chain end-to-end distances at high spatial (nm) and temporal resolutions (~s). We will discuss how to establish a synthetic platform to streamline the preparation of donor, acceptor-labeled polymers and how to use this end-to-end FRET technique for investigating chain dimensions as a function of solvent quality for polymer chains with different molecular weights. This talk will also cover how we extend this characterization platform to understand polymer thin film confinement effects on microscopic chain structures, which provides an important mechanism for their material property deviation compared to the bulk state.

Direct measurement of polymer chain conformations through end-to-end FRET

ACS Spring 2022

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