Electrofluidic Circuit-Based Microfluidic Viscometer for Analysis of Newtonian and Non-Newtonian Liquids under Different Temperatures

Abstract

This paper reports a microfluidic viscometer with an integrated pressure sensor based on electrofluidic circuits, which are electrical circuits constructed by ionic liquid-filled microfluidic channels. The electrofluidic circuit provides a pressure-sensing scheme with great long-term and thermal stability. The viscosity of the tested fluidic sample is estimated by its flow resistance, which is a function of pressure drop, flow rate, and the geometry of the microfluidic channel. The viscometer can be exploited to measure viscosity of either Newtonian or non-Newtonian power-law fluid under various shear rates (3-500 1/s) and temperatures (4-70 °C) with small sample volume (less than 400 μL). The developed sensor-integrated microfluidic viscometer is made of poly(dimethylsiloxane) (PDMS) with transparent electrofluidic circuit, which makes it feasible to simultaneously image samples under tests. In addition, the entire device is disposable to prevent cross-contamination between samples, which is desired for various chemical and biomedical applications. In the experiments, viscosities of Newtonian fluids, glycerol water solutions with different concentrations and a mixture of pyrogallol and sodium hydroxide (NaOH), and non-Newtonian fluids, xanthan gum solutions and human blood samples, have been characterized. The results demonstrate that the developed microfluidic viscometer provides a convenient and useful platform for practical viscosity characterization of fluidic samples for a wide variety of applications.

Design and Fabrication of a Microfluidic Viscometer Based on Electrofluidic Circuits

“…The working principles of the pressure-sensing scheme in this device are detailed in References [ 18 , 24 , 25 , 26 ]. Inside a microfluidic channel, the fluidic viscosity ( μ ) is proportional to the flow resistance ( R flow ), this resistance is proportional to the pressure drop along this channel (Δ P ), and this pressure drop generates a hydraulic pressure ( P H ) at the pressure-sensing area, causing changes in the cross-sectional area (Δ A ) and the electrical resistance (Δ R ) of the electrofluidic circuit.…”

“…This resistance change is then measured by means of the electrofluidic Wheatstone bridge. The present microfluidic viscometer offers some advantages as compared to that shown in the article published earlier this year [ 18 ]. Firstly, the sample-pretreatment layer can be used to mix and/or dilute liquid samples.…”

“…Other microfluidic viscometers based on diffusion, surface tension, velocimetry, flow rate sensing, and pressure sensing were also reported [ 17 ]. The state-of-the-art techniques in designing and fabricating microfluidic rheometers and viscometers are detailed in References [ 18 , 19 , 20 , 21 , 22 , 23 ].…”

“…This microfluidic device consists of a PDMS layer for electrofluidic circuits, a thin PDMS membrane, another PDMS layer for sample pretreatment, and a glass substrate. The ionic liquid-based electrofluidic circuit can monitor pressure changes by measuring the corresponding resistance changes in the circuit; the working principles are detailed in References [ 18 , 24 , 25 , 26 ]. 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.…”

How fast is a snail’s pace? The influences of size and substrate on gastropod speed of locomotion

“…During movement, mucus is secreted from a ventral pedal gland, cells on the foot’s surface and the mantle collar (Campion, 1961; Buyssens, 2004). Pedal mucus is a non‐Newtonian substance and has a finite yield stress (Chan et al ., 2005; Lai et al ., 2010; Lee et al ., 2018). Under small stress, it remains highly viscous as an adhesive solid, allowing the snail to remain attached to a substrate.…”