Non-Newtonian Droplet Generation in a Cross-Junction Microfluidic Channel.

Maryam Fatehifar,Masoud Jabbari,Alistair Revell

doi:10.3390/polym13121915

Abstract

A two-dimensional CFD model based on volume-of-fluid (VOF) is introduced to examine droplet generation in a cross-junction microfluidic using an open-source software, OpenFOAM together with an interFoam solver. Non-Newtonian power-law droplets in Newtonian liquid is numerically studied and its effect on droplet size and detachment time in three different regimes, i.e., squeezing, dripping and jetting, are investigated. To understand the droplet formation mechanism, the shear-thinning behaviour was enhanced by increasing the polymer concentrations in the dispersed phase. It is observed that by choosing a shear-dependent fluid, droplet size decreases compared to Newtonian fluids while detachment time increases due to higher apparent viscosity. Moreover, the rheological parameters—n and K in the power-law model—impose a considerable effect on the droplet size and detachment time, especially in the dripping and jetting regimes. Those parameters also have the potential to change the formation regime if the capillary number () is high enough. This work extends the understanding of non-Newtonian droplet formation in microfluidics to control the droplet characteristics in applications involving shear-thinning polymeric solutions.

Highlights

Inspired by the lack of adequate research, the present study numerically investigates the non-Newtonian power-law droplet formation in a flow-focusing channel model while the continuous phase is Newtonian
Increasing the xanthan gum concentration changes the rheological behaviour of the dispersed phase by increasing the apparent viscosity and degree of shear-thinning
Non-Newtonian behaviour affected the droplet size and the influence became more apparent as the flow deviated more from being Newtonian

Summary

Introduction

Microfluidic technology (c.f. Figure 1a), capable of controlling and manipulating minuscule amounts of fluid in micrometre channels, has attracted researchers since the start of the 21st century [1], and gained broad attention after 2010 due to its promising potential to be used in biomedical and biochemical studies. Microfluidics has shed light on droplet generating/sorting where each of the formed immiscible droplets acts as an isolated reactor. The volume of droplets is within the range of nanolitre to picolitre (15 and 200 μm diameter) [2], meaning that amount of reagent and samples used are very small. After the formation of droplets, with each containing the targeted species/cells, further steps including detection, mixing, reaction kinetic study, biochemical analysis, drug delivery and biomedical diagnosis can be executed [3]

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Conclusion