Abstract
This article details the mathematical model of a microfluidic device aimed at separating any binary heterogeneous sample of microparticles into two homogeneous samples based on size with sub-micron resolution. The device consists of two sections, where the upstream section is dedicated to focusing of microparticles, while the downstream section is dedicated to separation of the focused stream of microparticles into two samples based on size. Each section has multiple planar electrodes of finite size protruding into the microchannel from the top and bottom of each sidewall; each top electrode aligns with a bottom electrode and they form a pair leading to multiple pairs of electrodes on each side. The focusing section subjects all microparticles to repulsive dielectrophoretic force, from each set of the electrodes, to focus them next to one of the sidewalls. This separation section pushes the big microparticles toward the interior, away from the wall, of the microchannel using repulsive dielectrophoretic force, while the small microparticles move unaffected to achieve the desired degree of separation. The operating frequency of the set of electrodes in the separation section is maintained equal to the cross-over frequency of the small microparticles. The working of the device is demonstrated by separating a heterogeneous mixture consisting of polystyrene microparticles of different size (radii of 2 and 2.25 μm) into two homogeneous samples. The mathematical model is used for parametric study, and the performance is quantified in terms of separation efficiency and separation purity; the parameters considered include applied electric voltages, electrode dimensions, outlet widths, number of electrodes, and volumetric flowrate. The separation efficiencies and separation purities for both microparticles are 100% for low volumetric flow rates, a large number of electrode pairs, large electrode dimensions, and high differences between voltages in both sections.
Highlights
Microfluidic devices are those devices with flow passages smaller than 1000 μm, and this brings about certain advantages including a reduced need for sample and reagents, reduced power consumption, portability, and small footprint [1,2]
One of the applications for which microfluidic devices are employed includes the separation of a heterogeneous mixture of microparticles into multiple homogeneous samples; the homogeneity could be in terms of size or type
The first part of this section demonstrates the ability of the microfluidic device in achieving separation based on size with sub-micron resolution; for this, the model is used for demonstrating the ability of the device in separation a heterogeneous mixture of 2-μm and 2.25-μm polystyrene microparticles suspended in water (ρm = 998 kg/m3, μm = 10−3 Pa·s), based on size [8]
Summary
Microfluidic devices are those devices with flow passages smaller than 1000 μm, and this brings about certain advantages including a reduced need for sample and reagents, reduced power consumption, portability, and small footprint [1,2]. The net DEP force experienced by microparticles, in the microfluidic device, is type-dependent, thereby allowing for achieving separation based on type. The small microparticle passes over the electrodes unaffected while the big microparticle is pushed along the width, of the microchannel, by nDEP force, thereby achieving separation based on size. Alnaimat et al [8] modeled the functioning of a microfluidic device, with planar IDT electrodes on the bottom surface of the microchannel, employed for type-based separation. This frequency of operation is selected such that one type of microparticle is subjected to pDEP while the other type of microparticle is subjected to nDEP. The model developed for the proposed microfluidic device is three-dimensional, thereby allowing to account for microparticle’s displacement along the height of the microchannel; this is crucial when handling microparticles with density different from that of the medium and is, a merit of the model
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