(160f) Microfluidic Device for the Continuous Measurement of Viscosity

Viscosity is an important variable in chemical processes that is commonly used to monitor the extent of a reaction, the quality of an end product, and the design and optimization of flow systems, among other applications. The accurate measurement of viscosity usually involves sample collection for batch testing that can take hours before analysis is completed. If viscosity is being used as a quality control parameter, the delay in response can prevent actions to correct the process and may not even indicate the current state of the system. We have developed a microfluidic device that can measure viscosity of aqueous solutions in a fast and continuous way.

The device operates by pumping the sample and an immiscible oil phase into a cross junction where droplets are created. At low capillary numbers, the regime our device operates, the mechanism that controls the droplet formation is flow rate breakup, which relates the length of the droplets to their viscosity. Previously we have presented that our device has a linear relationship between droplet length and viscosity, with the results being in agreement with cone-and-plate rheometer measurements. In this talk we will present an optimized design that works with a variety of Newtonian and non-Newtonian fluids including Boger fluids and Xanthan gum solutions. We have also used our device for continuous measurement of viscosity by monitoring the coagulation process in blood at different shear rates. Each device costs only a few dollars to fabricate and can respond to changes in viscosity in the order of seconds. Additionally it can operate using small sample volumes of only nanoliters per hour. These advantages make our technology appealing in chemical industry and biomedical devices that require viscosity measurements in a continuous, inexpensive, fast and reliable way.