Design and Fabrication of a Microfluidic Viscometer Based on Electrofluidic Circuits

Bo-Bi Tzeng,Yung-Shin Sun

doi:10.3390/mi9080375

Abstract

This paper reports a microfluidic viscometer based on electrofluidic circuits for measuring viscosities of liquid samples. The developed micro-device consists of a polydimethylsiloxane (PDMS) layer for electrofluidic circuits, a thin PDMS membrane, another PDMS layer for sample pretreatment, and a glass substrate. As the sample flows inside the microfluidic channel, its viscosity causes flow resistance and a pressure drop along this channel. This pressure drop, in turn, generates a hydraulic pressure which deforms the PDMS membrane, causing changes in the cross-sectional area and the electrical resistance of the electrofluidic resistor. This small resistance change is then measured via the electrofluidic Wheatstone bridge to relate the measured voltage difference to the fluidic viscosity. The performance of this viscometer was first tested by flowing nitrogen gas with controllable pressures into the device. The relationship between measured voltage difference and input gas pressure was analyzed to be linear in the pressure range of 0–15 psi. Another test using pure water indicated good linearity between measured voltage difference and flow rate in the rate range of 20–100 μL/min. Viscosities of glycerol/water solutions with volume/volume (v/v) concentrations ranging from 0 to 30% were measured, and these values were close to those obtained using commercially available viscometers. In addition, the sample-pretreatment layer can be used to mix and/or dilute liquid samples to desired concentrations. Therefore, this microfluidic device has potential for measurements of fluidic viscosity in a fast, accurate, and high-throughput manner.

Highlights

Viscosity is an important fluidic property that occurs between two surfaces of that fluid moving at different velocities
Estimates of urine viscosity provide a better characterization of the biological system and should result in more accurate modeling of bladder hyperthermia treatments [1]
To investigate the pressure-sensing performance, nitrogen gas was introduced into the microfluidic channel to deform the PDMS membrane

Summary

Introduction

Viscosity is an important fluidic property that occurs between two surfaces of that fluid moving at different velocities. The same group fabricated a self-calibrating, micro-fabricated capillary viscometer for analyzing non-Newtonian fluids [13] This glass-made device monitored the capillary pressure-driven movement of the fluid sample whose velocity and shear rate varied with time. The idea of turning this pressure sensor into a viscometer is as follows: inside a microfluidic channel, the flow resistance increases with increasing fluidic viscosity, and this increasing flow resistance, in turn, increases the pressure drop along this channel This pressure drop generates a hydraulic pressure at the pressure-sensing area, causing changes in the cross-sectional area and the electrical resistance of the electrofluidic circuit. This microfluidic viscometer is capable of measuring low-viscosity liquids: a glycerol solution of 2.5% (v/v in water) was measured to have a viscosity of 0.94 cP (the viscosity of water is around 0.89 cP at 25 ◦C)

Design and Fabrication of the Microfluidic Chip

Gas and Pure Water Test

Comparison with Other Devices

Findings

Conclusions