Measurement of local chemical reaction rate in a microchannel by using luminol chemiluminescence

• The local chemical reaction rate was estimated by using the chemiluminescence.
• The luminol chemiluminescence reaction clearly shows the mixing layer.
• Relationship between the local mixing and the chemical reaction rate was discussed.

The present paper reports local mixing and chemical reaction in a T-junction microchannel investigated using luminol chemiluminescence (CL). Generally, the degree of mixing in a microchannel is calculated based on the deviation of the obtained concentration profiles from the uniform concentration using a fluorescence technique. In the present study, the luminol CL reaction is applied to estimate the local chemical reaction rate at the interface between two liquids in the microchannel. Luminol emits blue chemiluminescence when it reacts with hydrogen peroxide at the mixing layer. Experiments were carried out using a T-junction microchannel 200 μm in width and 50 μm in depth that was cast in a PDMS chip. The chemiluminescence intensity profiles clearly show the mixing layer at the interface between the two liquids. The experimental results are compared with the results of a numerical simulation that involves solving mass transport equations that include a chemical reaction term. By calibrating the CL intensity to the chemical reaction rate estimated by the numerical simulation, the local chemical reaction profile can be quantitatively estimated from the CL intensity profile. The effects of the chemical species concentrations on the local mixing and the chemical reaction were investigated.