Electron microscopy and small angle x-ray studies of amorphous polymers

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Abstract
The small-angle X-ray scattering (SAXS) from polycarbonate, polymethyl methacrylate, and polyethylene terephthalate seem inconsistent, both in the magnitude of the SAXS intensity and in its variation with scattering angle, with nodular features as representative of the bulk polymers. Rather than nodules, the SAXS data indicate the presence of thermal density fluctuations frozen-in at the glass transitions, together with a small concentration of large heterogeneities (hundreds to thousands of angstroms in size). Electron microscopy (EM) of amorphous polycarbonate provides further support for the suggestion that nodular features are not representative of the bulk material. The only structure seen in bright field is the “salt and pepper” background common to all materials. In dark field, very small structures (<30 Å in size) occupying small volume fractions were observed. These results are at variance with previously reported EM observations of nodular features in polycarbonate. It is suggested that the structure of these polymers be regarded as that of a random amorphous solid, and that the nodular structures may reflect surface features of the materials.