Measurement of fluid viscosity based on droplet microfluidics

We demonstrate an efficient method that can precisely measure the viscosity of fluids based on droplet microfluidics. For our design of the droplet microfluidic viscometer, the volume of the fluid sample required for testing the fluid viscosity is on the order of nanoliters. In particular, a T-junction microdroplet generator is designed for the production of monodisperse droplets, and the flow rates of the continuous and dispersed phases are controlled by the pressure-driven microfluidic device. By giving a specified viscosity of the dispersed phase, the viscosity of the continuous phase can be measured, while considering the linear relation between the droplet length and the flow-rate ratio of the two phases, the linear relation between the droplet length and the viscosity ratio of the two phases can be obtained. For our design of the T-junction microdroplet generator, the viscosity ratio of the two phases can be predicted by testing the length of droplets formed in the microchannel, and therefore, the fluid viscosity of the continuous phase can be calculated. More importantly, the comparison between the measured and the given viscosity of the continuous phase is provided for three different geometries of the T-junctions, and consequently, the testing precision of the fluid viscosity can be validated experimentally.