Next-Generation ATR-IR Devices for Monitoring Chemical Processes

Ketki Srivastava, Bdhanya Ramaswami, Henk-Willem Veltkamp, Nicole Boyle, Grace Flaman, Johan G. Bomer, Albert van den Berg, Ward van der Stam, Ian Burgess, Mathieu Odijk

Research output: Chapter in Book/Report/Conference proceedingConference contributionAcademicpeer-review

Abstract

Miniaturization and microfluidics have garnered immense attention from industry and academia in the past few decades.[1], [2] Its advantages, such as the consumption of fewer reagents, reduced time scales for applications, and low cost and high throughput, have enabled great research in chemical analytics, where microreactors are used.[3] In this work, we show the fabrication of a microreactor consisting of a single-bounce attenuated total internal reflection (ATR) accessory coupled with a microfluidic channel to achieve spatially and temporally resolved kinetic information of an ongoing chemical reaction. Compared to our previous device[4], micromixers are added to the microfluidic channels to establish homogenously mixed liquids, enabling us to conduct reaction rate kinetic studies more easily.
The device consists of a silicon part with the internal reflection element (IRE) for infrared (IR) spectroscopy and the first halves of the micromixers. The glass part of the device contains inlets and outlets and the second halves of the micromixers. To achieve efficient mixing, a rotational gradient micromixer was used, the design of which was inspired by F.T.G. van den Brink et al.[5]. The geometry was explicitly designed for use in shallow channels (h<<w) and operates so that after each unit, the concentration gradient undergoes a clockwise rotation due to strategically placed ridges next to where the connecting necks are located. This drastically increases the mixing performance of the device as the critical dimension affecting the diffusional mixing spans across the channel's height instead of the channel's width. To confirm the mixing efficiency of the devices, COMSOL simulations were conducted for flowrates ranging between 0.1 µL/min and 30 µL/min with varying diffusion coefficients (1·10-8 m2/s to 1·10-10 m2/s). It was determined that with 6 rotational units, 100% mixing efficiency could be achieved at the highest flow rate of 30 µL/min.Various optimizations in the process flow were also performed to successfully fabricate this device. First, the deep reaction ion etching (DRIE) recipe was optimized to 50 cycles with 5s etch time to achieve black-silicon-free channels. Second, two thermal annealing cycles of 75s at 1100˚C followed by 1 min HF strip were performed to reduce bottom channel surface roughness, which could negatively affect the signal-to-noise ratio. The fabricated devices were then successfully used to monitor an SN2 chemical reaction.
Original languageEnglish
Title of host publicationNext-Generation ATR-IR Devices for Monitoring Chemical Processes
Publication statusPublished - 9 Jul 2024

Keywords

  • NLA

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