Why is the formation process of zeolites a particularly tough question? Heimo Schnablegger, a former senior scientist at the Max Planck Institute for Colloids and Interfaces and now product manager for SAXSess at Anton Paar GmbH, explains: "Small particles are hard to observe. Particularly their formation in liquids is still a mostly speculated-about topic. The reason for this is that particles pop into existence at unpredictable times and at more or less random places. Theoretical attempts to explain nucleation-and-growth processes are numerous but need experimental validation. Reliable investigation techniques are vital for these endeavors. The required equipment is either homemade or provided by companies who have the expertise to comply with the required specifications."
Basically, two techniques are commonly favored for the investigation of these small particles: Electron Microscopy and Small-Angle X-Ray Scattering (SAXS).
"Electron Microscopy," says Schnablegger, "gives clear pictures of the particles in a small selected sample area. Their shape and size can be viewed directly and in high resolution, provided that one looks at the right spot at the right time. This difficulty is overcome by freezing all motion inside the sample, so that a particular time snapshot can be investigated at leisure and in detail."
Small-Angle X-ray Scattering is the other method. Schnablegger explains the advantages of SAXS: "The whole sample volume - and not just a small part therefrom - can be investigated at the same time, so that good average values are obtained at once. It confirms the results of microscopy and adds statistical significance to it. The samples are usually investigated in vitro, i.e., without sample freezing, drying, or other preparation techniques that have the potential to destroy the structures before you can even look at them."
The cooperation between the University of Minnesota and Anton Paar GmbH applied the mechanistic principles of nanoparticle evolution to zeolite crystals, achieving a new level of understanding: Small particles of silica were observed to form in quite a uniform and narrow size range. These primary particles then self-assembled into an ordered (crystalline) superstructure, the precursors of zeolites. Get more information at
The application of SAXess is not limited to the investigation of silica nanoparticles. It has already been used to characterize proteins, viruses, paints, emulsions, micelles, vesicles, cellulose, and many types of synthetic polymers. Application notes on many of these topics can be requested from Anton Paar's homepage http://www.anton-paar.com.
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