Structure Determination of Interacting Sample Systems
Evaluation of interacting (charged or concentrated) particles requires the knowledge of “form and structure factor”. The unique GIFT software allows to study samples in their original state and to determine the nanostructure of the particles.
Form factor and Structure factor
Two different factors contribute to a small-angle X-ray scattering curve I(q), as shown in Figure 1:
- the form factor P(q) contains information about the size and shape of the single particles,
- the structure factor S(q) includes contributions from interactions between neighboring particles.
Fig. 1 Scattering curve with P(q) and S(q)
For the determination of the interaction of particles in e.g. charged or concentrated sample systems, the software needs to calculate the structure factor. S(q) is then used to correct the experimental curve in order to obtain the size and shape of a single particle.
Experimental and Results
A concentrated solution of micelles was analyzed with the SAXSpace system in line-collimation mode. The experimental scattering curve I(q) is shown in Figure 1. The intensity decay of I(q) at small scattering angles indicates structural interaction of the nanoparticles. Data evaluation without calculating the structure factor would give unacceptable and wrong results.
Program GIFT1 was used to evaluate the scattering data. The structure factor S(q) and the form factor P(q) were determined simultaneously and independently. P(q) was then used to derive the particle structure. Furthermore, the internal structure of the particles was evaluated by converting the Pair-distance distribution function into the radial electron-density profile using program DECON1. Figure 2 shows that the studied micelles have a core-shell structure.
Fig. 2 Radial electron-density profile
The SAXSpace system with the unique GIFT software enables to easily determine the structure of interacting samples. The ability to analyze samples in their original concentration is of special importance, since dilution might change the sample behavior.
1 O. Glatter, J. Phys.: Condens. Matter 18 (2006) 2403