How boundaries shape chemical delivery in microfluidics

Aminian, Manuchehr; Bernardi, Francesca; Camassa, Roberto; Harris, Daniel M.; McLaughlin, Richard M.

doi:10.1126/science.aag0532

Cited by 46 publications

(71 citation statements)

References 26 publications

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“…To quantify the deviation from the Gaussian distribution, skewness and kurtosis equations (42) and (43) condition and velocity profile (Aminian et al, 2016;Chatwin, 1970). The concentration distributions of the four cases are positively skewed for t < 0.5, because the point source release at the top of the canopy leads to the solute concentrate near the canopy layer at a small time.…”

Section: Modified Vertical Mean Concentration Distributionmentioning

confidence: 99%

Transient Solute Dispersion in Wetland Flows With Submerged Vegetation: An Analytical Study in Terms of Time‐Dependent Properties

Guo

Jiang

Chen

2020

Water Resources Research

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Predicting the concentration distribution of solute transport in vegetated flows is significant for associated environmental applications in water resources. While a semianalytical study has been made for the steady dispersion with a continuous release (Rubol et al., 2016, https://doi.org/10.1002/2016WR018907), an in‐depth analytical investigation has yet to be performed for the more complicated case of transient dispersion due to an instantaneous release. In regard to the pioneering benchmark observation (Murphy et al., 2007, https://doi.org/10.1029/2006WR005229) of transient solute dispersion in a submerged vegetated flow for an instantaneous source release at the top of the canopy, an extensive analytical effort is paid in this work to derive the time‐dependent basic properties and to investigate the temporal evolution of concentration distribution. Obtained large‐time asymptotic dispersivities agree well with available experimental results (Murphy et al., 2007, https://doi.org/10.1029/2006WR005229), with higher significance ( R2=0.87, n=24) for correlation between analytical results and experimental data. Analytical solutions covering effects of dispersivity, skewness, and kurtosis of detailed concentration distribution are compared satisfactorily with numerical results obtained by the random displacement method. The findings illuminate the applicability of this analytical approach in environmental risk assessment and water quality management.

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Section: Modified Vertical Mean Concentration Distributionmentioning

confidence: 99%

Transient Solute Dispersion in Wetland Flows With Submerged Vegetation: An Analytical Study in Terms of Time‐Dependent Properties

Guo

Jiang

Chen

2020

Water Resources Research

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“…The evolution of a passive scalar distribution in a prescribed laminar shear flow is given by the solution to the following nondimensional partial differential equation (PDE):

\frac{\partial T}{\partial τ} + Pe u false(y, z false) \frac{\partial T}{\partial x} = Δ T,

where T is the scalar concentration, and

u (y, z)

is the pressure‐driven shear flow given by the solution to the Poisson equation:

Δ u = - 2,

where the nondimensionalization is the same as given in Ref. . The parameter

Pe

, is the Peclet number, which gives the relative importance of fluid advection to molecular diffusion.…”

Section: Passive Transportmentioning

confidence: 99%

“…Recently, we established the surprising role which the cross‐sectional tube shape plays in establishing the symmetry properties of a diffusing passive scalar advected by a laminar shear flow. Specifically, using a combination of analysis, simulations, and physical experiments, it was shown that the aspect ratio alone may be used to control the upstream–downstream solute distribution whereby tubes whose cross section have an exaggerated aspect ratio (“thin” tubes) yield distributions which are front‐loaded, having more mass arriving at the target before the mean arrives on long, diffusive timescales.…”

Section: Introductionmentioning

confidence: 99%

“…All other polygons require infinite series representations, or other numerical constructions of the fluid flow. In turn, the analysis to compute the long‐time skewness asymptotics was generally developed in our prior work, and relies upon the inversion of a family of nested Poisson problems, similarly requiring numerical inversion in polygonal domains. We apply this analysis, using finite element solvers, and establish remarkably that the only polygonal domain yielding negative long‐time solute negative skewness is the triangle.…”

Section: Introductionmentioning

confidence: 99%

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Mass distribution and skewness for passive scalar transport in pipes with polygonal and smooth cross sections

2018

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We extend our previous results characterizing the loading properties of a diffusing passive scalar advected by a laminar shear flow in ducts and channels to more general cross-sectional shapes, including regular polygons and smoothed corner ducts originating from deformations of ellipses. For the case of the triangle and localized, crosswise uniform initial distributions, short-time skewness is calculated exactly to be positive, while long-time asymptotics shows it to be negative. Monte Carlo simulations confirm these predictions, and document the timescale for sign change. The equilateral triangle appears to be the only regular polygon with this property-all others possess positive skewness at all times. Alternatively, closed-form flow solutions can be constructed for smooth deformations of ellipses, and illustrate how both nonzero short-time skewness and the possibility of multiple sign switching in time is unrelated to domain corners. Exact conditions relating the median and the skewness to the mean are developed which guarantee when the sign for the skewness implies front (more mass to the right of the mean) or back (more mass to the left of the mean) "loading" properties of the evolving tracer distribution along the pipe. Short-and longtime asymptotics confirm this condition, and Monte Carlo simulations verify this at all times. The simulations are also used to examine the role of corners and boundaries on the Stud Appl Math. 2018;141:399-417.wileyonlinelibrary.com/journal/sapm

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“…Despite significant theoretical contributions, these works lack experimental proceedings to test the developed theories and simulations. Similarly, Aminian et al reported with theoretical and experimental evidence that cross-sectional aspect ratio alone could control the shape of the concentration profile of a solute plug in the axial direction [27], however, they primarily concerned themselves with long-term flow behavior, which is not directly applicable to many LoC processes requiring well-behaved solute distribution within a short timescale of injection. Recently, Gökçe et al reported self-coalescence-based control of reagent reconstitution by implementing a special geometric feature-capillary pinning line-into the shallow microfluidic channel [28].…”

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confidence: 99%

Flattening of Diluted Species Profile via Passive Geometry in a Microfluidic Device

et al. 2019

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In recent years, microfluidic devices have become an important tool for use in lab-on-a-chip processes, including drug screening and delivery, bio-chemical reactions, sample preparation and analysis, chemotaxis, and separations. In many such processes, a flat cross-sectional concentration profile with uniform flow velocity across the channel is desired to achieve controlled and precise solute transport. This is often accommodated by the use of electroosmotic flow, however, it is not an ideal for many applications, particularly biomicrofluidics. Meanwhile, pressure-driven systems generally exhibit a parabolic cross-sectional concentration profile through a channel. We draw inspiration from finite element fluid dynamics simulations to design and fabricate a practical solution to achieving a flat solute concentration profile in a two-dimensional (2D) microfluidic channel. The channel possesses geometric features to passively flatten the solute profile before entering the defined region of interest in the microfluidic channel. An obviously flat solute profile across the channel is demonstrated in both simulation and experiment. This technology readily lends itself to many microfluidic applications which require controlled solute transport in pressure driven systems.2 of 11 channel [13][14][15]. However, EOF heavily relies on the electrical properties of the medium and surface, for instance, imperfections or chemical coatings on the channel surface can distort the concentration profile [16,17]. Moreover, the application of an electric field can potentially be incompatible with nonhomogeneous solutes/buffers used in the device and may have negative effects on biological samples [18,19]. It can also be difficult to use electroosmotic flows for particular processes, such as mixing particles, due to the irrotational nature of the flow [20,21]. Recently, flat concentration profiles could be generated through magnetohydrodynamic (MHD) pumping [22]. To allow for effective MHD, the introduction of redox species to the fluid element is necessary. Thus, controlling the concentration profile in a microfluidics device without dependency on the liquid composition remains a challenge.Pressure-driven flows introduced with a mechanical syringe pump provide a simple and inexpensive alternative when EOF is not compatible with a device or the sample [13,23]. However, it is well known that a pressure gradient through a channel will introduce a parabolic flow profile in the axial direction. This is due to the no-slip condition found at the channel wall, which causes a non-uniform velocity gradient along the cross section of the channel [24]. Considering a two-dimensional (2D) cross-section of a rectangular channel, this effect is proportional to channel dimensions and much more significant in the axial dimension of a typical device. Accordingly, the introduction of such a parabolic profile prevents precise solute transport within the device.Related literature on the topic of Taylor dispersion in microfluidic channels has suggested that pa...

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How boundaries shape chemical delivery in microfluidics

Cited by 46 publications

References 26 publications

Transient Solute Dispersion in Wetland Flows With Submerged Vegetation: An Analytical Study in Terms of Time‐Dependent Properties

Transient Solute Dispersion in Wetland Flows With Submerged Vegetation: An Analytical Study in Terms of Time‐Dependent Properties

Mass distribution and skewness for passive scalar transport in pipes with polygonal and smooth cross sections

Flattening of Diluted Species Profile via Passive Geometry in a Microfluidic Device

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