Investigating Aggregation Using In Situ Electrochemistry and Small-Angle Neutron Scattering

Using small-angle neutron scattering to investigate the aggregation of self-assembling molecules is well established. Some of these molecules are electrochemically useful, for example, in electrochromic devices. Electrochemistry can also be used in some cases to induce aggregation. Here, we describe an approach whereby electrochemistry can be directly carried out on a sample in the neutron beam, allowing us to monitor changes directly in situ. We exemplify with two examples but highlight that there are many other potential opportunities.

S3 the small amount of Pt gauze in the cell, after neutron exposure, the cell was monitored for any induced radioactivity before removing from the setup. Figure S1. Left -cartoon of the LabOmak UF-spectro-electrochemical cell used in the in situ SANS. Right -zoomed in image of the working, reference and counter electrodes in the quartz cuvette.
For the NDI-GF experiments, the electrochemistry was collected using a 2-or 3-electrode setup, depending on whether it was performed in the in situ cell, or ex situ windows. Reduction and oxidation potentials found from the 2-electrode set up were used for the FTO window cell described in the 'ex situ' section, whereas potentials found from the 3-electrode set up were used in the beamline experiments.
All data were collected using a 2-electrode setup without reference. Values cannot therefore be stated in reference to a known value. Cyclic voltammograms were carried out using a solution of hydroquinone dissolved in 1 M KCl as the electrolyte. A comparison of the position of the peaks corresponding to the well-defined and recorded quinone-hydroquinone redox reaction in the window cell setup can be made to the same measurement taken in a referenced electrochemical setup (CH Instruments and BASi).
Comparing to a referenced set up, solutions were deposited (5 mL) into a glass vial (CH Instruments) before electrodes were placed into solution. This setup comprised of a glassy carbon working electrode, Pt counter electrode and an Ag/AgCl reference (BASi). Reduction S4 and oxidation potentials reported must be taken in reference to these more well-defined shifted values, Table S1. The data were reduced to 1D scattering curves of intensity vs. Q using the facility provided software. The electronic background was subtracted, the full detector images for all data were normalized and scattering from the empty cell was subtracted. The scattering from D 2 O was also measured and subtracted from the data. Most of the data were radially averaged to produce the 1D curves for each detector position. The instrument-independent data were then fitted to the models discussed in the text using the SasView software (Version 4.2.2). 3 The SLD of the solvent was calculated to be 6.39x10 -6 Å -2 . The SLD of NDI-GF was 3.174 x10 -6 Å -2 and for BrNapAV 2.071 x10 -6 Å -2 . The best fit was decided to be that which fit well to the data and had the lowest Chi 2 value.    Solutions were prepared as previously described using deuterated solvent and base. All solutions were prepared with deuterated buffers. pD was adjusted using 0.1M NaOD and DCl.

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Samples were transferred to an FTO window cell and reduced and oxidised using -2.5 and 0.5 V respectively ( Figure S5). These values were taken from cyclic voltammograms (Table   S2). Figure S5. Schematic diagram of the FTO window setup described above.  Figure S5, S6 and Figure S9 shows this setup. The glass was sonicated in ethanol at 40°C for 30 minutes prior to assembly and gloves were used throughout to prevent fingerprints on the glass. Pieces of copper tape were added to the edges of the cell to ensure good contact between the cell and the crocodile clips from the PalmSens4 potentiostat. Solutions that were electrochemically used were transferred to and from FTO window cells to carry out electrochemical reduction and oxidation. Solutions were then transferred to a quartz cuvette and measured approximately one week later. Solutions were prepared before arrival on site in advance due to the restrictions in place at the time regarding COVID-19 and postal samples, Figure S6.    Figure S9. Images of the neutral and reduced colouration of buffered NDI-GF at 10 mg/mL adjusted to pH 9.2. Colouration occurred as a result of application of -2.7 V for 10 seconds.