Phase separation of multiphase droplets in a digital microfluidic device

Mun Mun Nahar,Hyejin Moon

doi:10.1186/s40486-019-0099-0

Mun Mun Nahar, Hyejin Moon

Open Access

https://doi.org/10.1186/s40486-019-0099-0

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Abstract

This study reports the first comprehensive investigation of separation of the immiscible phases of multiphase droplets in digital microfluidics (DMF) platform. Electrowetting-on-dielectric (EWOD) actuation has been used to mechanically separate the phases. Phase separation performance in terms of percentage residue of one phase into another phase has been quantified. It was conceived that the residue formation can be controlled by controlling the deformation of the phases. The larger capillary number of the neck forming phase is associated with the larger amount of deformation as well as more residue. In this study, we propose two different ways to control the deformation of the phases. In the first method, we applied different EWOD operation voltages on two phases to maintain equal capillary numbers during phase separation. In the second method, while keeping the applied voltages same on both sides, we tested the phase separation performance by varying the actuation schemes. Less than 2% of residue was achieved by both methods, which is almost 90% improvement compared to the phase separation by the conventional droplet splitting technique in EWOD DMF platform, where the residue percentage can go up to 20%.

Highlights

In recent years, solvent extraction and partitioning processes have been miniaturized into lab-on-a-chip devices due to their favorable position in terms of better mass transfer efficiency, higher specific interfacial area, and the lower consumption of reagents compared to classical macroscale approaches [1]
Case 1: Different applied voltages In this case study, electrowetting on dielectric (EWOD) device with conventional square shape electrodes were used and tests were run to compare the effect of applied voltages
Phase separation was performed by pulling a multiphase droplet from opposite directions as voltages were applied to two side electrodes next to the droplet

Summary

Introduction

Solvent extraction and partitioning processes have been miniaturized into lab-on-a-chip devices due to their favorable position in terms of better mass transfer efficiency, higher specific interfacial area, and the lower consumption of reagents compared to classical macroscale approaches [1]. Liquid–liquid micro extraction processes have been performed for separation and partitioning of cells, proteins, molecules, and ions in various applications [2,3,4,5,6,7,8] These processes utilize the interface between two immiscible liquids. Phase separation has been achieved by adding surfactant [9], by using structured microchannels with differing wettability [10], by surface treatments [8, 11,12,13] or by combining several techniques [14, 15] Most of these methods utilize laminar parallel flows in microchannels.

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