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Microfluidic mixing: a review.

Lee CY, Chang CL, Wang YN, Fu LM - Int J Mol Sci (2011)

Bottom Line: In such devices, sample mixing is essentially achieved by enhancing the diffusion effect between the different species flows.Many mixers have been proposed to facilitate this task over the past 10 years.Accordingly, this paper commences by providing a high level overview of the field of microfluidic mixing devices before describing some of the more significant proposals for active and passive mixers.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Engineering, National Pingtung University of Science and Technology, Pingtung 912, Taiwan; E-Mail: leecy@mail.npust.edu.tw.

ABSTRACT
The aim of microfluidic mixing is to achieve a thorough and rapid mixing of multiple samples in microscale devices. In such devices, sample mixing is essentially achieved by enhancing the diffusion effect between the different species flows. Broadly speaking, microfluidic mixing schemes can be categorized as either "active", where an external energy force is applied to perturb the sample species, or "passive", where the contact area and contact time of the species samples are increased through specially-designed microchannel configurations. Many mixers have been proposed to facilitate this task over the past 10 years. Accordingly, this paper commences by providing a high level overview of the field of microfluidic mixing devices before describing some of the more significant proposals for active and passive mixers.

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(A) Schematic diagram of channel with ridges; (B) Optical micrograph showing a top view of a red stream and a green stream flowing on either side of a clear stream in the channel and (C) Fluorescent confocal micrographs of vertical cross sections of the microchannel [66].
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f15-ijms-12-03263: (A) Schematic diagram of channel with ridges; (B) Optical micrograph showing a top view of a red stream and a green stream flowing on either side of a clear stream in the channel and (C) Fluorescent confocal micrographs of vertical cross sections of the microchannel [66].

Mentions: Stroock et al. [66] proposed an active micromixer based on electrohydrodynamic (EDH) forces. In such mixers, an EDH force is created by applying an electrical field to a bulk flow in which both an electrical conductivity gradient and a permittivity gradient exist (Figure 15). Vijayendran et al. [67] presented a three-dimensional serpentine micromixer designed to induce a chaotic mixing effect. The mixing efficiency of the serpentine microchannel was observed to be twice that obtained in a conventional straight microchannel. Liu et al. [68] considered a three-dimensional serpentine mixer, and a staggered herringbone mixer (Figure 16), and performed numerical simulations to investigate the mixing characteristics of the two devices for different Reynolds number regimes and fluorescent sample mass fractions. At Re = 1, the mixing performance of both mixers varied inversely with the mass fraction of the sample due to the dominance of molecular diffusion. However, when the Reynolds number was increased to 10, the inverse trend was observed in the serpentine mixer. This phenomenon was attributed to an enhanced flow advection effect at large sample mass fractions. However, this effect was not observed in the herringbone mixer when the Reynolds number was increased over a similar range. Liu et al. [69] fabricated a three-dimensional serpentine micromixer featuring a “C-shaped” repeating unit designed to induce chaotic advection. The results showed that for flows with a Reynolds number of 70, the mixing efficiency in the serpentine channel was 16 times higher than in a conventional straight channel and 1.6 times better than in a zigzag channel. Chen et al. [16] investigated a folding flow micromixer in the Stokes flow regime (Figure 17). Both the simulated and experimental results revealed a significant effect on mixing from a small misalignment of the glass layers that formed the mixer geometry. A layer offset of 5 μm (1.5% of channel width) produced a variation of up to a 26% in the measurement of the mixture uniformity, and improved or worsened depending on the precise offsets of the layers. In 2009, Kamg et al. [17] simulated and optimized a set of variables (i.e., sense of rotation of two rotational flows, aspect ratio of channel and ratio of bypass channel to whole width) and found at proper combination of the variables, almost global chaotic mixing was observed in the Stoke flow regime. Moon et al. [18] presented a strategy for the forced assembly of immiscible polymer into targeted structures via development of a planar polymer micro-mixer. The mixer drove streams of molten polymer through mixing chambers, which were fabricated from metal shims that contained flow channels. By stacking the shims, complex 3D mixing flows could be generated. The advantages of the mixing technology include sample sizes significantly less than traditional micro-mixers (<100 mg), simple reconfiguration of the flow geometry and optical access to the flow.


Microfluidic mixing: a review.

Lee CY, Chang CL, Wang YN, Fu LM - Int J Mol Sci (2011)

(A) Schematic diagram of channel with ridges; (B) Optical micrograph showing a top view of a red stream and a green stream flowing on either side of a clear stream in the channel and (C) Fluorescent confocal micrographs of vertical cross sections of the microchannel [66].
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3116190&req=5

f15-ijms-12-03263: (A) Schematic diagram of channel with ridges; (B) Optical micrograph showing a top view of a red stream and a green stream flowing on either side of a clear stream in the channel and (C) Fluorescent confocal micrographs of vertical cross sections of the microchannel [66].
Mentions: Stroock et al. [66] proposed an active micromixer based on electrohydrodynamic (EDH) forces. In such mixers, an EDH force is created by applying an electrical field to a bulk flow in which both an electrical conductivity gradient and a permittivity gradient exist (Figure 15). Vijayendran et al. [67] presented a three-dimensional serpentine micromixer designed to induce a chaotic mixing effect. The mixing efficiency of the serpentine microchannel was observed to be twice that obtained in a conventional straight microchannel. Liu et al. [68] considered a three-dimensional serpentine mixer, and a staggered herringbone mixer (Figure 16), and performed numerical simulations to investigate the mixing characteristics of the two devices for different Reynolds number regimes and fluorescent sample mass fractions. At Re = 1, the mixing performance of both mixers varied inversely with the mass fraction of the sample due to the dominance of molecular diffusion. However, when the Reynolds number was increased to 10, the inverse trend was observed in the serpentine mixer. This phenomenon was attributed to an enhanced flow advection effect at large sample mass fractions. However, this effect was not observed in the herringbone mixer when the Reynolds number was increased over a similar range. Liu et al. [69] fabricated a three-dimensional serpentine micromixer featuring a “C-shaped” repeating unit designed to induce chaotic advection. The results showed that for flows with a Reynolds number of 70, the mixing efficiency in the serpentine channel was 16 times higher than in a conventional straight channel and 1.6 times better than in a zigzag channel. Chen et al. [16] investigated a folding flow micromixer in the Stokes flow regime (Figure 17). Both the simulated and experimental results revealed a significant effect on mixing from a small misalignment of the glass layers that formed the mixer geometry. A layer offset of 5 μm (1.5% of channel width) produced a variation of up to a 26% in the measurement of the mixture uniformity, and improved or worsened depending on the precise offsets of the layers. In 2009, Kamg et al. [17] simulated and optimized a set of variables (i.e., sense of rotation of two rotational flows, aspect ratio of channel and ratio of bypass channel to whole width) and found at proper combination of the variables, almost global chaotic mixing was observed in the Stoke flow regime. Moon et al. [18] presented a strategy for the forced assembly of immiscible polymer into targeted structures via development of a planar polymer micro-mixer. The mixer drove streams of molten polymer through mixing chambers, which were fabricated from metal shims that contained flow channels. By stacking the shims, complex 3D mixing flows could be generated. The advantages of the mixing technology include sample sizes significantly less than traditional micro-mixers (<100 mg), simple reconfiguration of the flow geometry and optical access to the flow.

Bottom Line: In such devices, sample mixing is essentially achieved by enhancing the diffusion effect between the different species flows.Many mixers have been proposed to facilitate this task over the past 10 years.Accordingly, this paper commences by providing a high level overview of the field of microfluidic mixing devices before describing some of the more significant proposals for active and passive mixers.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Engineering, National Pingtung University of Science and Technology, Pingtung 912, Taiwan; E-Mail: leecy@mail.npust.edu.tw.

ABSTRACT
The aim of microfluidic mixing is to achieve a thorough and rapid mixing of multiple samples in microscale devices. In such devices, sample mixing is essentially achieved by enhancing the diffusion effect between the different species flows. Broadly speaking, microfluidic mixing schemes can be categorized as either "active", where an external energy force is applied to perturb the sample species, or "passive", where the contact area and contact time of the species samples are increased through specially-designed microchannel configurations. Many mixers have been proposed to facilitate this task over the past 10 years. Accordingly, this paper commences by providing a high level overview of the field of microfluidic mixing devices before describing some of the more significant proposals for active and passive mixers.

Show MeSH