Small-Angle X-ray Scattering (SAXS)

Figure 1. SAXS equipment.

Features

SAXS is a method for evaluating the structure of a substance at room or elevated temperatures by analysing the scattering of X-rays that irradiate the substance at small angles of incidence (\(2\theta < 10{^\circ}\)).

The periodicity and orientation of structures sized 2-20 nm can be evaluated, as well as particle and pore distributions. Structurally periodic biomaterials such as proteins can also be evaluated.

Application Examples

• Evaluation of crystallinity and orientation of polymer materials

• Higher-order structural and microphase separation analysis of liquid crystal samples

• Particle size analysis of polystyrene nanoparticles

• Domain size analysis of polymers.

Principle

X-ray scattering from a periodic structure results in a profile shown in Figure 3. Each peak corresponds to a periodicity of the structure. By detecting X-rays scattered at small angles, it is possible to measure the periodic structures of molecular sizes (2-20 nm).

Figure 2. Principle of SAXS.

Figure 3. Example of scattering from a periodic structure.

The principle of intra-particle scattering is shown in Figure 4 and the resulting profile in Figure 5.

The slope of the profile reflects the size of the particles (voids), and its shape reflects the shape and size distribution. Large-(\(> 10{^\circ}\)) and small-(\(< 10{^\circ}\)) angle scattering correspond to structures of the Ångström and nanometre order, respectively.

Figure 4. Principle of intra-particle scattering.

Figure 5. Example of an intra-particle scattering profile

Data examples

Figure 6 shows an example of orientational evaluation of stretched tape, whereas Figure 7 shows structural evaluation examples of different liquid crystalline emulsifiers.

Figure 6. Alignment evaluation of a stretched polytetrafluoroethylene (PTFE) tape. The pseudo colour corresponds to the intensity of the scattered X-rays (white largest, black lowest). The black area in the centre is due to intentional blocking of the X-rays for protecting the detector.

Figure 7. Evaluation of different liquid crystalline emulsifier structures. d is the plane spacing. The numbers correspond to Miller indices.

Data delivery formats

• Scattering profile, particle size distribution, 3D structure: PDF files

• Numerical data of the above: CSV text files

Measurement specifications

Property	Value	Unit	Notes
Minimum sample dimensions	\[5 \times 5\]	\[mm^{2}\]
Maximum sample dimensions	\[10 \times 30\]	\[mm^{2}\]
Maximum sample thickness	10	mm
Measurement area diameter	1	mm	Depends on the slit size
Minimum sample amount	0.5	g	Powders
	0.5	ml	Liquids
Temperature range	25-375	\[{^\circ}\text{C}\]
Incident angular range	0.1-10	\[{^\circ}\]
Measurable period length and particle size	\[1 - 90\]	nm	Depends on slit size and the distance between the sample and the detector

Items for enquiries

• Purpose and scope of the analysis

• Sample information:

  1. Quantity, shape, composition, cleavage properties, availability of pre-analysis samples

  2. Sample structure and thickness of the sample

  3. Sample arrival date

• Delivery date:

  1. Desired delivery dates of preliminary and final results

  2. Handling instructions

• Other relevant information

Caution

• For the measurement of voids, prepare a reference sample without voids.

• In the case of solution samples, also prepare a reference sample consisting of the solvent.