In this paper, the design, modeling, fabrication and characterization of a planar passive microfluidic mixer capable of
mixing particulate laden flows at low Reynolds numbers (Re) is reported. Particle-based flow modeling was performed
using CFD-ACE+ software to simulate micromixer designs for efficient particle dispersion across microchannel cross-section.
The micromixer design developed herein incorporates rectangular shaped obstructions within the microchannel
to propel both the particles within the flow and the flow itself into the other half of the channel, thereby achieving
mixing. A simple technique to analyze and quantify particle mixing is also proposed. The developed particle
micromixer has a simple planar structure, thereby resulting in easy realization and integration with on-chip microfluidic
systems, such as micro total analysis systems or lab-on-a-chip.
Nanoparticles have potential applications in many areas such as consumer products, health care, electronics, energy and
other industries. As the use of nanoparticles in manufacturing increases, we anticipate a growing need to detect and
measure particles of nanometer scale dimensions in fluids to control emissions of possible toxic nanoparticles. At present
most particle separation techniques are based on membrane assisted filtering schemes. Unfortunately their efficiency is
limited by the membrane pore size, making them inefficient for separating a wide range of sizes. In this paper, we
propose a passive spiral microfluidic geometry for momentum-based particle separations. The proposed design is
versatile and is capable of separating particulate mixtures over a wide dynamic range and we expect it will enable a
variety of environmental, medical, or manufacturing applications that involve rapid separation of nanoparticles in real-world
samples with a wide range of particle components.
A passive microfluidic mixer with high performance is designed and fabricated in this work. Diamond-shaped obstacles
were chosen to split the flow into several streams, which are then guided back together after the obstacle. To keep
pressure drop low, the channel cross-sectional area was maintained equal to the input cross-sectional area, and this was
held constant throughout the device. The proposed design was modeled using computational fluid dynamics (CFD)
software. The effects of channel width, channel length, location of obstructions, and Reynolds Number (Re) were
investigated. The simulated results were verified experimentally. Simulation data showed that the designed micromixer
achieved 90% mixing at a channel length of 4.35 mm with pressure drop of 584 Pa at Re = 1, while experimental data for
Re = 0.1 showed 90% mixing at 7 mm. The mixer functions well especially at the low Re (Re = 0.1).
In this work the design and fabrication of a novel passive microfluidic mixer capable of achieving mixing in shorter
distances and lower Reynolds numbers (<i>Re</i>) is reported. Passive mixers typically rely on the channel geometry to
mix fluids, and many previously reported designs work efficiently only at moderate to high <i>Re</i> and are often difficult
to fabricate as they incorporate complex 3-D structures within the channel. The mixer design discussed in this work
achieves good mixing at low <i>Re</i>, has planar geometry and thus is simpler to fabricate and integrate with existing labon-
a-chip (LOC) technologies. The design incorporates triangular notches patterned along the channel walls to
laminate the flow, thus enhancing mixing. Numerical and experimental studies to determine the effect of the notch
dimensions and placement within the microchannel were carried out to optimize the mixing performance. Results
show that the final mixer design is efficient at mixing fluids at low <i>Re</i>. The mixer is fabricated in
polydimethylsiloxane (PDMS) bonded to glass slides and tested using fluorescence dyes. Results show that the new
design exhibit complete mixing at <i>Re</i> < 0.1 within 7 mm and thus will benefit a wide range of LOC applications
where space is limited.
In this paper, we report on design and fabrication of a passive microfluidic mixer capable of mixing at low Reynolds numbers (<i>Re</i>). Passive mixers typically use channel geometry to mix fluids, and many previously reported designs that work only at moderate to high Reynolds numbers and are often difficult to fabricate. Our design uses diamond-shaped obstructions inside the microchannel to break up and laminate the flow, thus enhancing mixing. Both numerical and experimental studies show that the mixer is efficient at mixing fluids at low Reynolds numbers. We benchmarked our mixer design against a conventional T-mixer. Results show that the new design exhibits rapid mixing at <i>Re</i> < 0.1. The new mixer has a planar design which is easy to fabricate and thus will benefit a wide range of lab-on-a-chip applications.
Our research group is interested in environmental sensing of heavy metals that are involved in pollution of aqueous environments. As a result, we are developing chemical sensors within integrated microfluidic systems for sensitive and selective detection of these pollutants. Our approach is to combine established chemical sensing strategies with microfluidic structures, especially in plastic devices, to achieve a total heavy metal analysis system. In this regard, the combination of three complementary techniques - optical waveguide spectroscopy, electrochemistry and chemical partitioning offers the required selectivity and sensitivity essential for many environmental samples. On-chip optical waveguide spectroscopy promises to yield the necessary high sensitivity but relies on fabrication of optical structures with a material of appropriate refractive index, optical quality, and chemical stability by methods consistent with established fabrication methods. SU-8, the epoxy-based negative photoresist, appears to satisfy these requirements and,
thus, has become one of our candidate materials for waveguide fabrication on plastic microchips. Although the SU-8 has
been previously used for waveguide fabrication, its optical properties and more specifically the influence of processing
conditions on resultant optical properties have not been thoroughly characterized. This work presents an evaluation of SU-8-based multimode waveguides on glass and plastic substrates. Optical constants of waveguides have been characterized by spectroscopic ellipsometric and prism coupling techniques. Additionally, using the latter method, evaluation of propagation losses of various structures with different thicknesses has been made. Ellipsometric and prism
coupling measurements gave comparable refractive indices for variously cured SU-8 waveguide materials. Prism coupling analyses proved to be more useful for analysis of the many SU-8 waveguide structures fabricated in the thickness range of 5 to 75 μm.
A new passive micromixer has been developed with a low dependence on Reynolds number. The mixer design contains obstructions inside the mixing microchannels to breakup the flow resulting in chaotic mixing. Using CFDRC ACE+ software the mixer was modeled and was shown to completely mix water and glycerin in less than 1 cm. The micromixer was fabricated in cyclic olefin copolymer (COC) using hot embossing with polydimethylsiloxane (PDMS) tools and evaluated using epifluorescence microcopy.