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Determination of electronic structures during chemical reactions remains challenging in studies which involve reactions in the millisecond timescale, toxic chemicals, and/or anaerobic conditions. In this study, a three-dimensionally (3D) microfabricated microfluidic mixer platform that is compatible with time-resolved X-ray absorption and emission spectroscopy (XAS and XES, respectively) is presented. This platform, to initiate reactions and study their progression, mixes a high flow rate (0.50–1.5 ml min−1) sheath stream with a low-flow-rate (5–90 µl min−1) sample stream within a monolithic fused silica chip. The chip geometry enables hydro­dynamic focusing of the sample stream in 3D and sample widths as small as 5 µm. The chip is also connected to a polyimide capillary downstream to enable sample stream deceleration, expansion, and X-ray detection. In this capillary, sample widths of 50 µm are demonstrated. Further, convection–diffusion-reaction models of the mixer are presented. The models are experimentally validated using confocal epifluorescence microscopy and XAS/XES measurements of a ferricyanide and ascorbic acid reaction. The models additionally enable prediction of the residence time and residence time uncertainty of reactive species as well as mixing times. Residence times (from initiation of mixing to the point of X-ray detection) during sample stream expansion as small as 2.1 ± 0.3 ms are also demonstrated. Importantly, an exploration of the mixer operational space reveals a theoretical minimum mixing time of 0.91 ms. The proposed platform is applicable to the determination of the electronic structure of conventionally inaccessible reaction intermediates.

Supporting information

zip

Zip compressed file https://doi.org/10.1107/S1600577521003830/ig5094sup1.zip
Mixer 3D CAD in compressed. STEP format.

zip

Zip compressed file https://doi.org/10.1107/S1600577521003830/ig5094sup2.zip
Mixer simulation file for COMSOL in compressed. mph format.

mp4

Moving Picture Experts Group (MP4) video file https://doi.org/10.1107/S1600577521003830/ig5094sup3.mp4
Supporting movie S1

mp4

Moving Picture Experts Group (MP4) video file https://doi.org/10.1107/S1600577521003830/ig5094sup4.mp4
Supporting movie S2

pdf

Portable Document Format (PDF) file https://doi.org/10.1107/S1600577521003830/ig5094sup5.pdf
Supporting information: Sections S1 to S9; Figures S1 to S11.


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