# Steady streaming viscometry of Newtonian liquids in microfluidic devices

## TL;DR

This paper introduces a new probe-free microfluidic technique for measuring the shear viscosity of Newtonian liquids using steady streaming around a cylinder, enabling accurate viscosity measurements of low-viscosity and volatile liquids.

## Contribution

A novel steady streaming microviscometer that calibrates with known liquids and measures viscosity without probes in microfluidic devices.

## Key findings

- Successfully calibrated with standard liquids.
- Able to measure low-viscosity liquids.
- Effective for volatile liquids.

## Abstract

We report a novel technique capable of measuring the kinematic shear viscosity of Newtonian liquids with steady streaming in microfluidic devices. This probe-free microrheological method utilizes sub-kilohertz liquid oscillation frequencies around a cylindrical obstacle, ensuring that the inner streaming layer is comparable in size to the cylinder radius. To calibrate the viscometer, the evolution of the inner streaming layer as a function of oscillation frequency for a liquid of known viscosity is characterized using standard particle tracking techniques. Once calibrated, we show how the steady streaming viscometer can be used to measure low-viscosity liquids and volatile liquids.