Abstract
A new sample environment for the observation of ongoing chemical reactions is introduced for small-angle neutron scattering (SANS) experiments which enables structural changes to be followed continuously across a wide Q-range in response to changes in the chemical environment. The approach is demonstrated and validated by performing single and multiple potentiometric titrations on an aqueous anionic surfactant solution (oligo-oxyethylene alkylether carboxylic acid in D2O) with addition times varying from 1 s to 2 h. It is shown that the continuous flow set-up offers considerable advantages over classical ‘static’ measurements with regards to sample throughput, compositional precision and the ability to observe fast structural transitions. Finally, the capabilities and ongoing optimisation of the sample environment are discussed with reference to potential applications in the fields of biology, colloidal systems and complex soft matter.
Highlights
Synchrotron SAXS sources enable the measurement of very small sample volumes with high time resolution[20], there are a number of reasons why they may not always be appropriate for the characterisation of soft condensed matter or biological structures
The combination of high compositional precision and time-resolution allows for the exploration of non-equilibrium states that would go unnoticed in a classical ‘static’ approach
small-angle neutron scattering (SANS) measurements were performed on the D11 instrument at the ILL neutron scattering facility in Grenoble with a wavelength of 6 Å and maximum flux of 108 neutrons cm-2s-1 at the sample p(1o MsitiionnD272.OTh) etoptDhe(=so -lluotgioCnD, 3wOh+e)roef the solutions was varied by addition of NaOD
Summary
Synchrotron SAXS sources enable the measurement of very small sample volumes (due to tightly focussed beams) with high time resolution (typical flux at the sample position is ~1013 photons s-1)[20], there are a number of reasons why they may not always be appropriate for the characterisation of soft condensed matter or biological structures. The challenge, is to exploit the improvements at the facility level and mitigate the effects of decreasing experimental time, by expanding the range of in-situ sample environments available on SANS instruments This will, in turn, allow the biological and soft matter communities to explore complex phenomena that have hitherto remained inaccessible to small-angle scattering experiments. A chemical reactor with a flow-through observation cell is presented which enables the effects of changes in chemical composition, e.g. due to ongoing chemical reactions, to be measured continuously This approach increases the informational content of the experiment, via high-throughput and compositional precision, it reduces the likelihood of data gaps arising whenever rapid transitions occur. The feasibility and capabilities of the set-up are demonstrated via an investigation of the morphological evolution that occurs in an aqueous surfactant system as a result of changes in pH and salt concentration
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