Infrared spectroscopic nano-imaging of molecular coupling and dynamics in poly-tetrafluoroethylene

In organic materials, local morphology and environment determine material properties through intra- and intermolecular coupling. Vibrational spectroscopy can be used as a sensitive probe to variations in molecular structure, coupling, and dynamics. However, conventional far-field spectroscopic imaging spatially averages over the molecular ensemble, obscuring the effects of the local chemical environment. Here, we use broadband and ultrafast scattering scanning near-field optical microscopy (s-SNOM) to image nanoscale heterogeneity in the technologically important polymer of polytetrafluoroethylene (PTFE). Probing symmetric and antisymmetric coupled C-F stretch vibrations, from their variations and correlations in vibrational solvatochromism we reveal spatial sub-ensembles and their arrangements from nanometer to micron length scale of ordered and disordered domains in as cast, stretched, and rubbed PTFE films. The work demonstrates the use of vibrational marker resonances as intrinsic labels and molecular rulers as sensitive probes of their local structural environment associated with materials functional properties.