SAXS nanostructure analysis

The following is a short summary on SAXS essentials. Are you just starting up in SAXS? Then this is perfect for you – lean back and enjoy this little introduction.

What SAXS is

Nanostructured sample

SAXS (Small-Angle X-ray Scattering) is a non-destructive method for investigating nanostructures in liquids and solids. Here’s the basic approach:
An X-ray beam is sent through or onto a sample containing nanostructures, such as proteins, macromolecules or quantum dots. The beam interacts with the electrons of the sample and is scattered. The detected scattering pattern is characteristic of the nanostructures and can be used to determine their size, shape, internal structure and more.
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SAXS parameters

SAXS is used to determine several parameters of nanostructured samples – the most common ones are:
• Shape
• Size
• Internal Structure
• Crystallinity
• Porosity

SAXSdetermines

>> Structure Determination of Interacting Sample Systems

Unique SAXS benefits

SAXS results are representative of an entire sample, so SAXS ideally complements methods that provide unique but local information, such as electron microscopy.
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Another essential benefit of SAXS is that it barely requires any sample preparation. This sets it apart from complementary techniques such as electron microscopy or NMR spectroscopy, which often require extensive sample preparation. And since SAXS allows in-situ measurements, preparation artifacts are avoided and the sample remains unchanged.
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SAXS also stands out for the fact that it can be used to investigate biological macromolecules in solution, under physiological conditions. This increasingly popular application known as Bio-SAXS is a vital tool in molecular biology, where the analysis of samples in their native state is essential for studying the dynamic processes the sample is involved in.

Different angles – different results

SAXS_WAXS

The scattered X-rays can be recorded at different angles. In SAXS, you analyze the scattering pattern at small angles, typically below <10° 2Θ, to probe nano-sized particles and domains in a size range from 1 nm to 200 nm, which scatter towards these small angles.

To investigate smaller structures, such as crystal lattices at the atomic level, you interpret the scattered X-rays at wider angles. This approach is called Wide-Angle X-ray Scattering (WAXS) or X-ray Diffraction (XRD). The obtained WAXS pattern enables you to analyze structures below nanometer size – as atoms and interatomic distances scatter towards wider angles.

GI-SAXS: At grazing incidence

GISAXS

GI-SAXS (GI = Grazing Incidence) is a rather new method used to investigate thin films with nanostructures on the substrate surface. For GI-SAXS analysis, the X-ray beam is set to graze a flat sample almost parallel to its surface. The scattered signal is a sampling of the structures on the surface or slightly below the surface, depending on the chosen angle of incidence.

Different beam shapes – different benefits

Point line collimation

Before scattering, the X-rays are transformed into a well-defined line-shaped or point-shaped beam. This process is called collimation.

A line-collimated beam has the advantage that it combines a high photon flux with a high scattering volume – which means measurement times can be dramatically shorter than with point collimation. The drawback of a line-collimated beam is that it can only probe isotropic samples. Therefore, a line-shaped beam is preferable for analyzing weakly scattering samples, such as proteins and other soft matter. A point-collimated beam can be used to also analyze anisotropic samples, such as fibers or porous solids. Point collimation allows you to probe small sample areas and determine their local nanostructure, with the drawback of longer measuring times.

>> Desmearing of Line-smeared Scattering Curves

Ultra-fast SAXS Measurements with Metal Jet

The MetalJet x-ray source uses a high-speed jet of liquid gallium alloy as the target material with a wavelength close to copper radiation. The self-regenerating metal jet anode can accept very high power loads.
Combined with advanced electron optics the MetalJet delivers significantly higher brightness and power than any other microfocus X-ray source on the market.

>> SAXSpoint with MetalJet Source

SAXS applications

Typical SAXS/WAXS/GISAXS applications over a broad range of diverse materials:

Surfactants and emulsions

Detergents, food and drug carrier materials, personal care products

>> An insight into the Structure of Copolymer Surfactants

>> An Insight into the Structure of Surfactants

>> Studying the Internal Structure of Lamellar Systems

Polymers and fibers

Semi-crystalline polymers, block copolymers, polymer blends, fibers

>> Collagen – A Validation Sample for SAXS Systems

Nanostructured surfaces (GISAXS)

Layered thin-film samples, mesoporous thin films, nanoparticle superlattices

>> Mesoporous thin films – Investigating the structure of multi-layered films by GISAXS

>> Grazing-Incidence Diffraction Studies on Pentacene Thin Films

>> Temperature-dependent GISAXS studies on thin films

Catalysts, porous materials

Mesoporous materials, catalysts for polymerization, gas purification, fuel cell materials

>> Structural Characterization of a Mesoporous Material

Nanocomposites

Nano-filled polymer composites (carbon nanotubes, clay)

>> Studying the Internal Structure of Carbon Nanotubes with SAXS

Liquid crystals

LC displays, food and drug delivery systems, membranes

>> Small Angle X-Ray Scattering with Microcrystalline Materials

>> Tracking the Phase Transitions of Phase-changing Materials

Colloidal particle dispersions

Nanocrystals, pigments, quantum dots

>> Quantum dots – Size determination by SAXS

>> Rapid Size Determination of CdSe Quantum Dots Synthesized by Microwave Irradiation

>> Size and Size Distribution of Gold Nanoparticles by SAXS

Biological materials

Biomembranes, lipids, peptides, proteins in solution

>> Fast SAXS Measurements of a Diluted Protein Solution

>> Integration of SAXS and NMR for structure determination of biomolecules

>> Protein Mass Determination using Small Angle X-Ray Scattering

>> Protein Shape Determination by Small Angle X-Ray Scattering

Pharmaceuticals

Excipients, formulations, quality control

>> Quality control of pharmaceutical excipients during storage and processing

>> Fast Structure Analysis of Pharmaceutical Excipients by SWAXS for Product Quality Control

Tensile Testing

>> Coir fibers – SWAXS studies of structural changes induced by tensile stress

External Links

SAXS nanostructure analyzers

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