For a truly non-destructive characterization of nanostructures, small angle X-ray scattering (SAXS) is an ideal method, and it can be performed to compliment other methods, e.g. atomic force microscopy or electron microscopy. SAXS can be used to obtain statistically relevant information about the three-dimensional nanostructural properties of the complete system in its native environment.
Polymer Clay Composites are stiff, have outstanding strength-to-weight ratio, and are resistant to corrosion and fatigue, this makes them an attractive material for automotive, aerospace and other engineering applications. Various dispersion regimes are possible based on the interaction between the polymer matrix and nanoclays.
Either the polymer can separate the clay platelets in order to prevent their mutual interaction (exfoliation), or the polymer can enter between the clay platelets (intercalation) (Figure 1). The exfoliated structure is preferred in a majority of practical applications. The structural information for this purpose is provided by SAXS. This article deals with the application of SAXS on polymer clay composites using the N8 HORIZON. Table 1 presents the instrument configuration needed for the study.
Figure 1. Intercalated and exfoliated structures.
Table 1. Instrument configuration
||Air-cooled microfocus X-ray source (IµS)
||SCATEX pinholes, 2x 550 µm
||2D VÅNTEC-500, SDD 650 mm
The N8 HORIZON was utilized to measure a poly-propylene (PP)/styrene-ethylene-butylene-styrene (SEBS)/clay nano-composite sample. To improve the particle dispersion of the clay in the PP matrix a compatibilizer, such as SEBS block copolymer, is added. The sample can be directly mounted onto the sample holder frame without any preparation. A two-dimensional (2D) frame of the background and the sample were collected for a time period of 1000 seconds.
Figure 2 indicates the background, which in this case was an empty chamber. Although the sample transmission was very low (0.3%) because of the thickness of the sample, data quality was adequate to evalute the data. Extending the time period for data collection did alter the results, but it did improve statistics. All of the measurements were taken at room temperature conditions.
Figure 2. 2D Frames, both shown with the same color code for the intensity.
The comprehensive DIFFRAC.SAXS evaluation package was used for data processing, including background subtraction and radial integration, and the subsequent data analysis.
Figure 3 shows the radially integrated data. The characteristic SAXS profile of the lamellar spacing of the polymer chains can be detected at low angles.
Figure 3. 1D data sets as a result of the radial integration.
Figure 4 indicates that this is more clearly seen in a Kratky plot. The distance (d) between the layers in the lamellar polymer structure can be computed from the location of the main peak at q = 0.024Å-1, using the equation: D = 2π / qpeak
The lamellar thickness obtained for this example is approximately 260Å.
Figure 4. Kratky plot of background-subtracted data.
There is no increase of intensity in the Kratky plot towards high q, this means that the structure for this example is nearly completely exfoliated.
This information has been sourced, reviewed and adapted from materials provided by Bruker AXS Inc.
For more information on this source, please visit Bruker AXS Inc.