Microchannel edge refractometry

The objective of the paper is to present an optical technique that allows to characterize in situ concentration fields in microfluidic systems. The technique is based on the measurement of the refraction index in the liquid phase, in the immediate vicinity of the walls that confine the fluids. We call this method microchannel edge refractometry. The method is non-intrusive. We describe the refractometry technique, using theory, numerics and experiments. We show a resolution and sensitivity on the order of 3 × 10−3 and 2 × 10−3, respectively. We apply the technique to analyze diffusion phenomena in T sensors, measure supersaturations and establish phase diagrams of ternary systems in dedicated microdevices.