Viscosity measurement based on the tapping-induced free vibration of sessile droplets using MEMS-based piezoresistive cantilevers

摘要

We report a simple technique to measure the free vibration of microlitre-sized droplets using an array of thirteen MEMS-based piezoresistive cantilevers and demonstrate its application for the measurement of viscosity. Because the damping of the free vibration of a liquid droplet is known to be affected by the viscosity of the liquid, measuring the vibration of a droplet allows the viscosity to be estimated from a dilute sample volume. However, conventional methods to measure the droplet vibration require sophisticated apparatuses, which hinder the development of a portable viscometer. Here, we show that MEMS-based piezoresistive cantilevers can be an excellent tool to measure the vibration of a sessile droplet due to the high sensitivity and simplicity of the readout scheme. Using the cantilever array, we analyse the normal force distribution on the contact area of a sessile droplet in the static state and during the vibration. Next, we show that the viscosity (from similar to 1-30 mPa s) can be estimated within an error of less than 10% from the attenuation rate of the cantilever output during the tapping-induced vibration of small droplets (similar to 2.4 mu L). In addition to the advantage of the small sample volume, the proposed viscometer has simple operation and readout schemes, which are desirable for many applications, including point-of-care testing and drug development.