Silicon Micromixers with Infrared Detection for Studies of Liquid-Phase Reactions

Abstract

We present an integrated microchemical system that combines micromixing, a reaction channel, an IR detection region, and temperature control for monitoring and kinetic studies of liquidphase reactions. The microdevices exploit the transparency of silicon to infrared radiation in most of the wavelength region of interest (4000-800 cm -1 ), the precise definition of microfluidic channels by deep reactive ion-etching, the high thermal conductivity of silicon, and the fusion bonding of silicon for fixed-path-length transmission cells. Two devices are considered, a simple T-shaped mixer and an efficient mixer with interleaving channels for rapid mixing. The first device is used to characterize IR transmission characteristics in silicon-based microreactors and to demonstrate the feasibility of monitoring exothermic reactions, the hydrolysis of propionyl chloride under isothermal conditions. The mixing characteristics of the second microreactor are evaluated experimentally by an acid-base reaction and predicted by computational fluid dynamics simulations. Typical mixing times are 25 ms. The alkaline hydrolysis of methyl formate, a reaction following second-order kinetics with a half-life of 70 ms, exemplifies the use of the microreactor in determining rate constants. The results demonstrate the main advantages of the integrated microchemical systems in reaction monitoring: faster mixing times, temperature control, in situ detection, and elimination of sample postprocessing.

Design and additive manufacture for flow chemistry

“…104 Inline measurements for IR are usually conducted by placing the microreactor into a commercial IR spectrometer sample compartment, or in a microscope stage connected to an FTIR spectrometer system. 108 The transparency of glass and silicon to FTIR radiation means these are ideal materials with which to manufacture microfluidic devices for FTIR analysis.…”

A Review on Mixing in Microfluidics

“…Floyd et al [8] fabricated a silicon microchannel with 10 inlets for mixing acid and base solutions ( Figure 6). Their experimental measurement for the mixing performance was compared with computational fluid dynamics (CFD) results with good agreement in terms of the residence time.…”

Unconventional detection methods for microfluidic devices

“…Another example of chip-based IR detection was shown for an integrated microsystem that combined micromixing, a reaction channel, temperature control, and an IR detection region [18], as shown in Fig. 1.…”

“…Bottom half: Expanded view of microreactor layers, top of wafer 2, buried channels in wafer 1 that would be visible from the backside of the wafer, and inlet ports in wafer 2. Reprinted with permission from [18].…”