Energy-loss measurements of polymer microstructure and polymer interfaces: Issues and opportunities

The traditional methods for studying polymer microstructure in the transmission electron microscope largely hinge on the use of differential heavy-element staining to induce amplitude contrast. However, adequate staining agents are not available for all polymer systems. Furthermore, nonlinearities in the distribution of stain, particularly at interfaces, degrade the achievable resolution. Spatially resolved electron energy loss spectroscopy (EELS), on the other hand, provides a new opportunity to study polymer microstructure by providing rich spectroscopic features and high spatial resolution. Translating this opportunity into practice is underpinned by three main factors: (1) the availability of spectral fingerprints distinguishing various polymers; (2) the limits of achievable resolution; and (3) the ultimate constraints imposed by electron irradiation. This study discusses these issues and demonstrates the use of spatially resolved EELS with examples from hydrocarbon homopolymer and homopolymer blends of polyphenylene sulfide (PPS) and polyethylene terephthalate (PET), nylon 6/high-density polyethylene (HDPE) and polystyrene/polyethylene (PS/PE).