Abstract
This study aimed to design and fabricate planar constricted–expanded structures that are integrated into paper-based channels in order to enhance their chaotic advection and improve their mixing performance. Chromatography papers were used to print paper-based microfluidics using a solid-wax printer. Three different constricted–expanded structures—i.e., zigzag, crossed, and curved channels—were designed in order to evaluate their mixing performance in comparison with that of straight channels. A numerical simulation was performed in order to investigate the mixing mechanism, and to examine the ways in which the planar constricted–expanded structures affected the flow patterns. The experimental and numerical results indicated that the proposed structures can successfully mix confluents. The experimental results revealed that the mixing indices (σ) rose from the initial 20.1% (unmixed) to 34.5%, 84.3%, 87.3%, and 92.4% for the straight, zigzag, curved, and cross-shaped channels, respectively. In addition, the numerical calculations showed a reasonable agreement with the experimental results, with a variation in the range of 1.0–11.0%. In future, we hope that the proposed passive paper-based mixers will be a crucial component in the application of paper-based microfluidic devices.
Highlights
Micro-electromechanical systems (MEMS) technology has been successfully utilized to develop a variety of micromixers, which can be incorporated into microfluidic systems or manipulated as standalone devices
At a microscale, mixing mechanisms are basically cataloged into two approaches for the promotion of mixing effects, namely, streaming advection, and chaotic advection [2]
These results indicated that the three planar constricted–expanded structures—namely, the zigzag, cross-shaped, and curved channels—achieved the highest mixing performance
Summary
Micro-electromechanical systems (MEMS) technology has been successfully utilized to develop a variety of micromixers, which can be incorporated into microfluidic systems or manipulated as standalone devices. The common external forces include the use of piezoelectrics, pneumatics, acoustics, electroosmosis, dielectrophoresis, magnetohydrodynamics, and electrowetting approaches, which are detailed in the review references [1,3,4] Such forces facilitate effective mixing and are easy to manipulate; active micromixers suffer from some drawbacks, such as the required additional components that raise fabrication costs, the need for large spaces, and difficult integrability. Microfluidic paper-based analytic devices (μPADs) have successfully demonstrated some benefits, including being lightweight, having a low cost, flexibility, portability, and effectiveness. The novelties of the proposed paper-based microfluidic mixers are their ease of design, rapid fabrication, low cost, and high mixing performance. Where P is the pressure vector, η is the fluid viscosity, CF is a quadratic drag factor, B is
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