Chemical kinetics and spectroscopy enabled by 3D hydrodynamic focusing and mixing in a 3D-printed microfluidic device

We have developed a three-dimensional (3D) hydrodynamic focusing and 3D-printed microfluidic mixer for chemical kinetics studied by X-ray absorption and emission spectroscopy (XAS/XES). To trigger reactions, our device co-flows a 30 \textmu L min-1 sample stream into a 1 mL min-1 sheath stream. This sheath focuses the sample from a 75 to 10 \textmu m hydraulic diameter within 500 \textmu s. After mixing sheath species into the sample stream, the sample stream is expanded to 50 \textmu m where XAS/XES measurements are performed. The residence times between mixing initiation and measurement are within 2.5 to 350 ms. The fused silica component of our device is a clear monolithic chip fabricated using a femtosecond laser exposure and chemical etching technique. This chip interfaces with a polyimide capillary which provides a low X-ray adsorption region. The system enables X-ray studies of order millisecond reactions, toxic chemicals, and/or anaerobic conditions. We will present the device design and fabrication and the development and experimental validation of convection-diffusion-reaction models. The models are quantitatively validated by (widefield and confocal) microscopy and by XAS/XES experiments of reacting ferricyanide and ascorbic acid. Our combined system and models are applicable to studies of the electronic structure of reaction intermediates.