Morphological characterization of polymer nanocomposites is a fundamental challenge that is complicated by multiple length scales. Here, we report a technique for high-throughput monitoring of interphase and dispersion in polymer nanocomposites based on Förster resonance energy transfer (FRET). Nanofibrillated cellulose (NFC), fluorescently labeled with 5-(4,6-dichlorotriazinyl)aminofluorescein (FL) and dispersed into Coumarin 30 (C30) trace-level-doped polyethylene (PE), is used as a model system to assess the effect of processing on cellulose dispersion. The extent of energy transfer, measured by fluorescent spectroscopy and confocal microscopy, is evaluated with FRET algorithms. FRET efficiency and its standard deviation are used to monitor the extent of interphase formation and homogeneity, respectively. Color-coded images are generated for a real space observation of energy transfer efficiency and reveal the interphase formation at a nanoscale while probing a macroscale area that is large enough to be representative of the entire sample. The unique ability of this technique to provide orientation and spatial information over six orders of magnitude in length scale discloses a new powerful tool for structure-property-processing investigation in polymer nanocomposites.
"Nanocomposite", "interphase", "fluorescence", "FRET", "confocal microscopy".