Understanding confinement effects on polymer chain conformation using Förster resonance energy transfer*

Advancements in nanotechnology demand film thickness to keep shrinking to the size of a molecule, which results in changes in material properties relative to their bulk state. While extensive studies have been pursued to investigate nanoconfinement effects on polymer glassy behaviors, fundamental relations between polymer chain structures and macroscopic film properties still lack a full understanding. This study aims to determine confinement effects on polymer chain conformation using Förster resonance energy transfer (FRET). This technique can detect the distance between a donor and acceptor fluorophore in close proximity at a nanometer length scale by the energy transfer efficiency between the two species. By labeling donor and acceptor fluorophores on polymer chain ends, FRET enables measurement of the averaged polymer chain end-to-end distances at high spatial (nm) and temporal resolutions (~s). We will discuss how to use this technique for investigating chain dimensions as a function of film thickness for polymers of various molecular weights. Furthermore, the conformation of polymer chains under strong confinement will be correlated with their mechanical property deviation compared to the bulk state.