Electroosmotic Flow of Viscoelastic Fluid through a Constriction Microchannel

Jianyu Ji,Zhaohui Liu,Shizhi Qian

doi:10.3390/mi12040417

Abstract

Electroosmotic flow (EOF) has been widely used in various biochemical microfluidic applications, many of which use viscoelastic non-Newtonian fluid. This study numerically investigates the EOF of viscoelastic fluid through a 10:1 constriction microfluidic channel connecting two reservoirs on either side. The flow is modelled by the Oldroyd-B (OB) model coupled with the Poisson–Boltzmann model. EOF of polyacrylamide (PAA) solution is studied as a function of the PAA concentration and the applied electric field. In contrast to steady EOF of Newtonian fluid, the EOF of PAA solution becomes unstable when the applied electric field (PAA concentration) exceeds a critical value for a fixed PAA concentration (electric field), and vortices form at the upstream of the constriction. EOF velocity of viscoelastic fluid becomes spatially and temporally dependent, and the velocity at the exit of the constriction microchannel is much higher than that at its entrance, which is in qualitative agreement with experimental observation from the literature. Under the same apparent viscosity, the time-averaged velocity of the viscoelastic fluid is lower than that of the Newtonian fluid.

Highlights

Electroosmotic flow (EOF) uses electric field to control fluid motion, and has been widely used in various microfluidic and nanofluidic applications such as fluid pump [1], mixing [2], and polymer translocation in biosensing [3]
Electroosmotic flow (EOF) of viscoelastic fluid through a 10:1:10 constriction microchannel is numerically investigated as functions of the applied electric field and the polymer concentration
We neglect the effect of the polymer concentration on the zeta potential of the channel walls

Summary

Introduction

Electroosmotic flow (EOF) uses electric field to control fluid motion, and has been widely used in various microfluidic and nanofluidic applications such as fluid pump [1], mixing [2], and polymer translocation in biosensing [3]. Bello et al [10] conducted the pioneering study on EOF of non-Newtonian fluid, and measured EOF velocity of methyl cellulose solution in a capillary Their results show that EOF velocity of such polymer solutions is much higher than that predicted with the classic Helmholtz-Smoluchowski velocity. Non-Newtonian effects can be characterized by proper constitutive models relating the dynamic viscosity and the rate of shear. Such constitutive models include power-law model [12], Carreau model [13], WhiteMetzner model [14], Bingham model [15], Oldroyd-B (OB) model [16], PTT model [17], Moldflow second-order model [18], Giesekus model [19], etc.

Methods

Results

Conclusion