Physical model and sensitivity analysis of volume metering in centrifugal microfluidics

Abstract

In the context of the Medicare project, precise micro-litre of liquid must be selected through a metering operation unit integrated into a centrifugal microfluidic chip. The experimenters have highlighted the dependency of the selected volume with respect to the shape of the liquid-air interface. As the experiments are expensive, numerical methods must be developed in order to study the sensitivity of the selected volume with respect to geometrical and physical parameters that must be identified.\\

A 3D model using the Surface Evolver program as well as a 2D analytical model have been developed in order to perform a sensitivity analysis on the selected volume with respect to the geometry of the chamber, the capillary length and the contact angle. By comparing the results of the two models with each other and with the experiments it has been proved that they both predict with accuracy the shape of the liquid-air interface and the volume in the chamber.\\

The results of the sensitivity analysis have demonstrated that there exists some proportionality between the volume and the geometrical and physical parameters of the experiments. In addition, it has been established that the volume is the most sensitive to the capillary number, and so to the centrifugal acceleration of the microfluidic chip, and to the depth of the metering chamber. Finally, the study of the impact of the height of the operation unit with respect to the contact angle has proven that several shapes of the interface can coexist for the same height. However, the range of height where this phenomenon could happen is of the order of a tenth of a millimetre.