Instrumental developments for anomalous small-angle X-ray scattering from soft matter systems

Abstract

An optimized instrument for anomalous small‐angle X‐ray scattering from charged soft matter is described. The experimental setup takes special care for single‐photon detection sensitivity, high energy resolution of the monochromator, in situ calibration of intensity and energy, and the avoidance of radiation damage. Measured intensities are normalized to an absolute scale online, which can be further decomposed to resonant and non‐resonant contributions. The performance of the instrument is demonstrated by an example involving cationic surfactant micelles with bromide counter‐ions. The counter‐ion profile around the micelle is deduced from the analysis of anomalous scattering near the K‐absorption edge of bromine. Two different approaches yield similar results for the radial profile of the counter‐ions, showing strong condensation of the counter‐ions on the micellar surface, in agreement with the inference from electrochemical methods.

Anomalous small-angle X-ray scattering from charged soft matter

“…Concerning 2D detectors and intensity monitors, SAXS requires single photon sensitivity and high spatial resolution which can be fulfilled by state-of-the-art CCD-based X-ray detectors (e.g. the FReLoN camera using fibre-optically coupled Kodak CCD image sensor) [11]. Alternatively, energy-resolving pixel detectors (e.g.…”

“…with ρ 0 (r) being the energy-independent scattering length density profile [11] (i.e. the usual contrast well below the absorption edge) and v(r) being the spatial distribution of the anomalous scattering units (e.g.…”

“…In the following the main requirements for quantitative ASAXS measurements is summarized. A more detailed description of a specific setup at ID02 beamline, ESRF (Grenoble, France) can be found elsewhere [11].…”

“…3.1), neglecting the often very small contribution of f below the K-edges. Alternatively, a linear system of equations (constituted from measurements at m ≥ 3 energies) can be represented by the following matrix equation and be solved numerically [11,13]:…”

Resonant elastic X-ray scattering: Where from? where to?

“…If no suitable high Z element is present in the macromolecules, extrinsic labelling techniques are used either to insert heavy atoms such as Se, Sr or lanthanides, or to substitute light metal atoms with heavier ones [49,[71][72][73].…”