Small-angle x-ray scattering makes sense of nanoparticles.
Small-angle x-ray scattering (SAXS) covers angles between 0.1° and 10° and allows investigation of particles on the order of nanometers. In SAXS, a sample containing particles is irradiated by an x-ray beam. The x-rays are scattered by the particles into all directions and constitute a scattering pattern at the detector.
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Modern materials technology goes “nano” because the presence, or the implementation of, nanostructures in a material can dramatically change its properties. It thus offers a huge potential to tailor synthetic materials.
Self-assembled and hierarchical nanostructured materials and the functions offered by these self-assemblies, such as micelles, liquid crystals, emulsions, liposomes, and solid-gels are used in a wide variety of industrial fields. In addition, nanostructured inorganic materials (composite titanium dioxide particles or mesoporous silicas) and modified biological substances (recombinant and purified proteins) are in great demand. Accurate measurement of the basic properties of these nanomaterials is essential because they are so widely used.
Two techniques are commonly favored when investigating nanostructures: electron microscopy and small-angle x-ray scattering (SAXS). In electron microscopy, the shape and size of nanostructures can be viewed directly and with high resolution, provided that one looks at the right spot at the right time. With SAXS the whole sample volume is investigated at a glance, so it gives good average values and adds statistical significance to the results obtained by electron microscopy. In contrast to electron microscopy, SAXS requires little sample preparation, minimizing the risk of destroying the structures before they can be seen. Another benefit of the technique is that samples can be studied in their natural environment, which helps to understand biological and metabolic processes.
In measurements, SAXS plays the field
Generally, SAXS allows one to investigate the structure of domains which are dispersed in a matrix material with particle sizes in the nanometer range, typically between 1 and 100 nm.
SAXS can provide information on: particle size and size distribution; particle shape (sphere, cylinder, lamella) and internal structure (core-shell); porosity (surface-to-volume ratio); order (crystallinity) and orientation of the particles; and molecular weight and aggregation number.
In a SAXS experiment the sample is irradiated by an x-ray beam. The nanostructures inside the sample scatter the beam in a characteristic, angle-dependent intensity distribution, which is recorded by a detector.
The result is a scattering pattern, which allows the researcher to make conclusions about the size and shape of the nanostructured sample under investigation.
As a large fraction of the sample is irradiated at the same time, the pattern always constitutes a statistical mean of all irradiated nanostructures. The actual structural information is retrieved from the scattering pattern by suitable data evaluation software.
The SAXSess nanostructure analyzer by Anton Paar GmbH, Ashland, Va., is a SAXS system that performs SAXS investigations in the laboratory for all different kinds of samples from liquids (colloids, proteins, surfactants) to solids (polymers, fibers, nano-composites).
High measurement speed in the SAXSess allows time-resolved investigations of dynamic processes that occur in the minute range. Owing to the TrueSWAXS feature, samples can be investigated in a wide angular range in a single measurement run. This provides quick information on the nanostructure and on the phase state, or crystal structure, of the sample. The large selection of sample holders allows different solid and liquid samples which require special precautions.
The SAXSess is useful for investigations of polymers, blends, composites, suspensions, ink, paper, aerogels, emulsions, creams, membranes, fibers, catalysts, viruses, proteins and more.
Particle sizing is of great interest when trying to gauge the effect changes in the surface-to-volume ratio and quantum-size has on nanoparticles. It's also important
when the stability of emulsions (e.g., oil droplets in water) and suspensions (e.g., enzymes, colloidal inorganic precipitates, etc.) is of concern. When an emulsion or suspension becomes unstable, the formation of aggregates with subsequent phase separation takes place. The SAXSess is a very sensitive tool to detect even a few aggregates at a very early stage, because they strongly influence the scattering signal.
In light of SAXS' ability to address rapid developments in nanomaterials, the technique will continue to grow in importance as a mainstream analytical method in materials research.
—Heimo Schnablegger, Product Manager SAXSess, Anton Paar,
