Application of defocus transmission electron microscopy to polymers

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Abstract
Image formation in polymer electron microscopy is discussed with particular reference to the defocus-contrast technique in which interfaces between regions with different electron densities can be imaged. This method is applied to semi-crystalline polymers, where the difference in density between amorphous and crystalline regions gives rise to the defocus contrast. While other techniques of imaging semicrystalline polymers (i.e., staining, ion etching, etc.) suffer from the fact that during the preparation uncontrolled changes in the structure of the polymer can occur, the defocusing technique permits the direct observation of the polymer structure. Furthermore, sequences of micrographs from the very same area can give information about molecular processes although the technique is limited by beam damage. Results are reported concerning lamellar crystallization, lamellar thickening during annealing, and the two-phase domain structure in segmented polyurethane, in addition to several general applications of the technique.