Microfluidic viscometer for measuring the viscosity of microliter-volume liquid samples

Abstract

A microfluidic viscometer measures the viscosity of a microliter-volume fluid sample using a microfluidic chip having a microchannel with a high aspect ratio (˜10), allowing the microflow therein to be approximated as a rectangular slit flow. The microfluidic chip is fabricated by stacking rigid sheet materials that can be laser cut to specified shapes and sizes. The microchannel, rendered smooth and hydrophobic by a repellant coating, provides a straight flow path for the sample to approach flow equilibrium as it moves through. By applying corrections related to the visual bias from the camera and the capillary pressure difference at the air-liquid interface, the viscosity of the fluid sample can be calculated based on differential pressure data, sample length, velocity, volumetric flow rate, and contact angle from captured video, and the channel dimension, given that the sample has reached a flow equilibrium condition.