Generation of Oil Droplets in a Non-Newtonian Liquid Using a Microfluidic T-Junction

Enrico Chiarello,Ladislav Derzsi,Evandro Piccin,Giampaolo Mistura,Matteo Pierno

doi:10.3390/mi6121458

Enrico Chiarello, Ladislav Derzsi + Show 3 more

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https://doi.org/10.3390/mi6121458

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Abstract

We have compared the formation of oil drops in Newtonian and non-Newtonian fluids in a T-junction microfluidic device. As Newtonian fluids, we used aqueous solutions of glycerol, while as non-Newtonian fluids we prepared aqueous solutions of xanthan, a stiff rod-like polysaccharide, which exhibit strong shear-thinning effects. In the squeezing regime, the formation of oil droplets in glycerol solutions is found to scale with the ratio of the dispersed flow rate to the continuous one and with the capillary number associated to the continuous phase. Switching to xanthan solutions does not seem to significantly alter the droplet formation process. Any quantitative difference with respect to the Newtonian liquid can be accounted for by a suitable choice of the capillary number, corresponding to an effective xanthan viscosity that depends on the flow rates. We have deduced ample variations in the viscosity, on the order of 10 and more, during normal operation conditions of the T-junction. This allowed estimating the actual shear rates experienced by the xanthan solutions, which go from tens to hundreds of s−1.

Highlights

Droplet-based microfluidics is a blossoming research field that presents great potential for high-throughput chemical and biological analysis, synthesis of advanced materials, sample pretreatment, protein crystallization, and encapsulation of cells [1,2,3,4,5,6]
This allowed the generation of oil droplets without the addition of any surfactant to the continuous phase
Newtonian Droplets in a Newtonian Continuous Phase emulsions was less than 2% at high flow rates of the continuous phase Qc and less than 10% at the lowest Qc

Summary

Introduction

Droplet-based microfluidics is a blossoming research field that presents great potential for high-throughput chemical and biological analysis, synthesis of advanced materials, sample pretreatment, protein crystallization, and encapsulation of cells [1,2,3,4,5,6] This technology relies on the production of pico- to nano-liter volume droplets at high throughput rates (typically 1–10 kHz) and with high uniformity. The dynamics of the break-up of the dispersed phase and the formation of drops are relatively well understood in the case of two immiscible Newtonian fluids as, for example water and oil [8,9,10] This investigation has been extended to viscoelastic non-Newtonian liquids in flow-focusing geometries and in T-junctions because of the potential interest in manipulating samples of physiological liquids such as blood, synovial fluid, or saliva. With careful adjustment of the ratio of viscosities of the two immiscible liquids, viscoelasticity of the focusing liquid could help to lower the dispersion of the emulsions and to decrease the volume of the produced droplets

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