Interdiffusion measurements in thermally controlled microchannel using infrared spectroscopic imaging

In many applications, knowledge of the mass diffusivity coefficient is mandatory to optimize the design and operating conditions of microfluidic devices and chemical reactions. The literature reports few values due to limited techniques, and the impact of the fluid temperature is rarely taken into account when the diffusivity is measured. In this study, we present an imaging method to investigate and quantify the interdiffusion of two fluids in a microchannel under controlled temperatures. The experimental setup combines a thermally controlled microfluidic chip and a microscale infrared (IR) spectroscopy imaging technique. The mass diffusivity of formic acid (HCOOH) in sulfuric acid (H2SO4) was measured from room temperature to 50°C to demonstrate the performance of the setup. This work offers a rapid tool and a methodology for accurate contactless interdiffusion measurements in thermally controlled T-shape reactors applicable a large set of chemicals.