X-ray microscopy of core-shell latex particles

Latex particles with internal structure are attractive for a number of applications, including coatings, adhesives, chemical delivery etc. Harald Stöver's group  (BIMR, Chemistry, McMaster) is developing novel latex systems. In order to optimize these structures for particular applications (e.g. pheromone delivery for environmentally benign, controlled release pest control) it is important to be able to chemically analyse their internal structure. In particular, although electron microscopy readily reveals internal structure of micron scale latex particles, it cannot distinguish chemical differences in the various regions (e.g. core versus shell) or whether the structure is simply a consequence of a density and/or thickness variation.

Scanning transmission X-ray microscopy using variable energy synchrotron X-rays provides the required spatially resolved chemical analysis. Images at different photon energies provide a means to quantify the relative contributions of chemical versus density/thickness contrast. The displayed images and spectra are from a recent study of acrylate-polystyrene latex particles which were synthesized in a two-step process to intentionally segregate all of the poly-acrylate component to the shell region. The exquisite sensitivity of NEXAFS microscopy to the chemical basis for this structure is clear.

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