Sizing Nanoparticles with X-Rays

P. Hoghoj, S. Desvergne-Blenau, F. Bossan, M. Fernandez-Martinez, B. Lantz, R. Mahe, P. Panine, S. Rodrigues
Xenocs, FR

Keywords: characterization, nanoparticles, sizing

Summary:

Small Angle X-Ray Scattering (SAXS) is a technique suited for measurements of nanoparticle size and size-distributions. Through careful implementation, SAXS can also give absolute particle concentrations. The technique has many similarities to light scattering methods, but also a number of important differences: The extremely short wavelength used (typically 0.154 nm) makes the technique sensitive to the size of even very small nano-particles. We will show measurements of nano-particles with diameter in the range from a few nm to more than 200 nm. In fact, as size decreases, the measurement becomes easier as opposed to other techniques such as Dynamic Light Scattering (DLS) which generally have issues when measuring very small nanoparticles. Furthermore, the x-ray measurements are much less sensitive to multiple scattering phenomena extending the scattering techniques towards concentrated samples. We will show examples of measurement of nanoparticle size-distributions and concentrations. Typically, nanoparticles being measured are suspended in a solvent, but as will be shown, it is also possible to obtain data from particles in a matrix such as a coating, even if the matrix is opaque. When compared to imaging methods it is important to realize that in SAXS the sample volume is typically 0.5 mm3 and that the result is representative of this sample volume. This is in contrast to nanoparticle sizing using imaging methods such as electron microscopy. Typically, the field of view is very small and the particles need to be applied to a surface for measurement one by one. While SAXS so far has been used mainly in R&D, we will show how the sample volume together with new instrumental developments makes it a good candidate for quality control in nanoparticle production. The use of SAXS for nanoparticle sizing is also encouraged by the work of the ISO standards committee ISO / TC24 / SC4 / WG10. The work of the committee has recently resulted in a draft ISO standard1. We will show different examples of particle sizing and size-distribution measurements with SAXS according to the ISO standard.