Optimization of scanning transmission X-ray microscopy for the identification and quantitation of reinforcing particles in polyurethanes

The morphology, size distributions, spatial distributions, and quantitative chemical compositions of co-polymer polyol-reinforcing particles in a poly urethane have been investigated with scanning transmission X-ray microscopy (STXM). A. detailed discussion of microscope operating procedures is prese nted and ways to avoid potential artifacts are discussed. Images at selecte d photon energies in the C 1s, N 1s and O 1s regions allow unambiguous iden tification of styrene-acrylonitrile-based (SAN) copolymer and polyisocyanat e polyaddition product-based (PIPA) reinforcing particles down to particle sizes at the limit of the spatial resolution (50 nm). Quantitative analysis of the chemical composition of individual reinforcing particles is achieve d by fitting C Is spectra to linear combinations of reference spectra. Regr ession analyses of sequences of images recorded through the chemically sens itive ranges of the C Is, N Is and Ols spectra are used to generate quantit ative compositional maps, which provide a fast and effective means of inves tigating compositional distributions over a large number of reinforcing par ticles. The size distribution of all particles determined by STXM is shown to be similar to that determined by TEM. The size distributions of each typ e of reinforcing particle, which differ considerably, were obtained by anal ysis of STXM images at chemically selective energies. (C) 2001 Elsevier Sci ence B.V. All rights reserved.