Crystallinity and Size of Nanoparticles can be Studied with Combined SAXS/WAXS Technique

SAXS/WAXS is becoming an increasingly popular technique for the characterization of nanoparticles. Equipment such as Xenocs' Nano-inXider SAXS/WAXS system allows researchers to study the size and crystallinity of nanoparticles.

Controlling the size of nanoparticles as well as their crystalline phase is critical to achieve or stabilize the final properties of many functionalized materials.

SAXS is gaining significant interest for assessing nanoparticles size distribution as measurement can be performed on a large probed volume (about 1 mm3) offering statistical information in a very accurate way with minimum sample preparation. Nanoparticles can thus be characterized not only diluted in solutions, but also within a polymer matrix or as a dry powder.  The technique is for example referenced in the 2012 JRC report of the European Commission about the definition of Nanomaterials, and new standard for nanoparticles sizing has been published recently - Ref 17867:2015 (Particle size analysis-Small Angle X-ray Scattering).

We show below an example of Fe3O4 nanoparticles characterization. The size of particles and the nature of the crystalline phase can strongly impact the very specific properties of ferrofluids. Characterization of size distribution and crystalline phase on a highly diluted solution of magnetite nanoparticles in toluene (with oleic acid as a stabilizer) was obtained through simultaneously measurement of the small and wide angle x-ray scattering properties.

The SAXS signal of the magnetite core was fitted with a spherical shape. SAXS analysis showed a mean radius of 8.64 nm.  Size distribution could be deduced through data fitting (Figure 1).

Figure 1. McSAS 1 graphical output showing the best fit on SAXS data of magnetite diluted solution obtained using the Monte Carlo method (left) and the volume-weighted size distribution associated with the MC fit (right). The distribution shows a mean dimension of 8.64 nm and a width (standard deviation, σ=√(variance)) of 3.68 nm.

At the same time, the Fe3O4 crystalline phase could be confirmed through WAXS analysis as displayed.

The experimental results were obtained using the Nano-inXider SAXS/WAXS system from Xenocs.

Running simultaneous SAXS and WAXS measurements increases the measurement throughput, and enables the simultaneous study of structure & crystalline phases under the same in-situ variable experimental conditions, avoiding misleading interpretations due to hysteresis effects.

Widely used in R&D, the SAXS/WAXS technique is a non destructive method complementary to microscopy and light scattering. New developments in instrumentation, software and methods bring new opportunities for use in process analysis and quality control.

This story was one of many featured in Xenocs' latest newsletter Exploring the Very Small. To read all of the articles in the newsletter please click here.

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