In-Situ SAXS on Transformations of Porous and Nanostructured Solids

Keywords:
SAXS, specific inner surface, real-time in-situ measurement

Abstract:
The characterization of micro- and mesoporous materials by conventional methods of porosimetry or imaging techniques requires the existence of essentially dry materials. Modern SAXS (small-angle X-ray scattering) methods overcome these limitations and allow the real-time in-situ monitoring of specific inner surface in reacting or transforming systems. Comparison with BET-surfaces on standard reference materials and internal cross-validation and by parallel tests have shown excellent agreement. Important examples for application are the sol-gel synthesis of mesoporous materials from aqueous micellar or liquid-crystalline reaction mixtures, or the dissolution of controlled-release, drug-containing microparticles. The in-situ observation of specific inner surface development by SAXS provides information on the kinetics and mechanism of the reactions and reveals control parameters for rational process and product optimisation. Equally, this technique opens the way for real-time studies on crystallization phenomena from amorphous materials, e.g. amorphous sucrose, or on aging/coarsening processes of microcrystalline powders, which are of high interest in pharmaceutical technology as drug excipients. There, the simultaneous observation of specific inner surface by SAXS, and of crystallinity by WAXS (wide-angle X-ray scattering) opens the scope for studies of nucleation and crystal growth. With recent instrumentation developments including the SpinCap technique, automatization and dedicated software tools, such measurements, previously the domain of synchrotron radiation, can be routinely performed in the normal laboratory. The time-resolution reaches down to the second-time scale, and therefore is suitable for studies on moderately fast transformation processes in solids.

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Nanotech 2005 Conference Program Abstract