Transient streaming potential in a finite length microchannel

We have developed electroosmotic pumps (EOPs) fabricated from 15-nm-thick porous nanocrystalline silicon (pnc-Si) membranes. Ultrathin pnc-Si membranes enable high electroosmotic flow per unit voltage. We demonstrate that electroosmosis theory compares well with the observed pnc-Si flow rates. We attribute the high flow rates to high electrical fields present across the 15-nm span of the membrane. Surface modifications, such as plasma oxidation or silanization, can influence the electroosmotic flow rates through pnc-Si membranes by alteration of the zeta potential of the material. A prototype EOP that uses pnc-Si membranes and Ag/ AgCl electrodes was shown to pump microliter per minute-range flow through a 0.5-mm-diameter capillary tubing with as low as 250 mV of applied voltage. This silicon-based platform enables straightforward integration of low-voltage, on-chip EOPs into portable microfluidic devices with low back pressures.lectroosmotic flow results from the interaction between an electric field and the diffuse layer of ions at a charged surface. In capillaries or pores, the migration of the diffuse layer toward the oppositely charged electrode causes the bulk fluid within the channel to flow through viscous drag. Electroosmotic pumps (EOPs) are designed to generate high flow rates in microchannels using these principles (1, 2). EOPs present a number of advantages over mechanical pumps, including the lack of mechanical parts, pulse-free flows, and ease of control through electrode actuation. EOPs have been suggested as pumps for cooling circuits (3) and microfluidic devices that aid in drug delivery (4, 5) or diagnostics (2, 6). Microfluidic devices enable the miniaturization of multistep laboratory processes into small, low-cost, disposable units (6, 7). The inclusion of multiple steps into a single device increases the need for the precision pumping of fluids on-chip.High voltages (>1 kV) are often required for direct current (dc) EOPs to achieve sufficient flow rates in microchannels (8, 9). However, devices with high-voltage EOPs require bulky external power supplies and a skilled technician to operate, which defeats the ease of use and portability aims of a microfluidic diagnostic tool. For these reasons, the development of a low-voltage EOP is a current focus in the literature. Several recent low-voltage EOPs have been fabricated from porous silicon (10), alumina (11-13), track-etched polymer (14), and carbon nanotube membranes (15). These low-voltage EOPs are much thinner than their highvoltage predecessors (60-350 μm compared with >10 mm). Yao et al. suggest that further thinning of EOPs will enable better voltage-specific characteristics (16). Here, we examine the electroosmotic pumping by nanoporous membranes that are more than two orders of magnitude thinner than any membrane material previously used in an EOP.We have recently developed an ultrathin (15-30 nm), nanoporous membrane material called porous nanocrystalline silicon (pnc-Si) (17). pnc-Si membranes are fabricated on silicon wafers usin...

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“…where E s is the streaming potential measured at zero current and P is the applied pressure through the membrane (24,27). In Eq.…”

Section: Significancementioning

confidence: 99%

High-performance, low-voltage electroosmotic pumps with molecularly thin silicon nanomembranes

Snyder

Getpreecharsawas

Fang

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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“…No-slip boundary conditions are invoked at all channel walls (u = 0). For BGE ion transport, a constant bulk ion concentration (c bulk ) is provided at both the inlet and outlet (Daiguji et al 2004a(Daiguji et al , 2006Mansouri et al 2005). For analyte transport, a constant sample concentration (c anal,in ) is set at the microchannel inlet.…”

Section: Methodsmentioning

confidence: 99%

“…Among other key findings, they captured the nonlinear electrokinetic behavior at the recovery stage due to the induced pressure, electroosmotic flow of the second kind, and complex flow circulation. Finite element method was also used in Mansouri et al (2005) to study transient streaming potential in a finite length microchannel of circular cross-section with the emphasis on the different time scales of establishing the streaming potential and the ion concentration field. The advancement in theory inspires the use of such nanoelectrokinetic phenomena for sample preconcentration in a diversity of LoC bioanalysis systems.…”

mentioning

confidence: 99%

Numerical analysis of electrokinetic transport in micro-nanofluidic interconnect preconcentrator in hydrodynamic flow

Wang

Pant

Chen

et al. 2009

Microfluid Nanofluid

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The phenomenon of enrichment of charged analytes due to the presence of an electric field barrier at the micro-nanofluidic interconnect can be harnessed to enhance sensitivity and limit-of-detection in sensor instruments. We present a numerical analysis framework to investigate two critical electrokinetic phenomena underlying the experimental observation in Plecis et al. (Micro Total Analysis Systems, pp 1038-1041, 2005b: (1) ion transport of background electrolytes (BGE) and (2) enrichment of analytes in the micro-nanofluidic devices that operate under hydrodynamic flow. The analysis is based on the full, coupled solution of the Poisson-Nernst-Planck (PNP) and Naviér-Stokes equations, and the results are validated against analytical models of simple canonical geometry. Parametric simulation is performed to capture the critical effects of pressure head and BGE ion concentration on the electrokinetics and ion transport. Key findings obtained from the numerical analysis indicate that the hydrodynamic flow and overlapped electrical double layer induce concentration-polarization at the interfaces; significant electric field barrier arising from the Donnan potential forms at the micro-nano interfaces; and streaming potential and overall potential are effectively established across the micro-nanofluidic device. The simulation to examine analyte enrichment and its dependence on the hydrodynamic flow and analyte properties, demonstrates that order-of-magnitude enrichment can be achieved using properly configured hydrodynamic flow. The results can be used to guide practical design and operational protocol development of novel micro-nanofluidic interconnect-based analyte preconcentrators.

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“…However, similar studies like [21][22][23][24][25][26][27] all assume that the capillary is infinitely long and the solution domain is the cross section of capillary without considering changes along the axis of the capillary. Mansouri et al [28] investigated the transient streaming potential in a finite length microchannel by solving the coupled governing equations simultaneously using finite element method thanks to the advances of numerical computing technology. Based on their work, a new capillary model is proposed in this paper by using trigonometric functions to better mimic the pore-throat structures in tight porous media.…”

Section: Introductionmentioning

confidence: 99%

Electrokinetic coupling in single phase flow in periodically changed capillary with a very small throat size

Zhang

Sun

2015

International Journal of Heat and Mass Transfer

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Transient streaming potential in a finite length microchannel

Cited by 52 publications

References 30 publications

High-performance, low-voltage electroosmotic pumps with molecularly thin silicon nanomembranes

High-performance, low-voltage electroosmotic pumps with molecularly thin silicon nanomembranes

Numerical analysis of electrokinetic transport in micro-nanofluidic interconnect preconcentrator in hydrodynamic flow

Electrokinetic coupling in single phase flow in periodically changed capillary with a very small throat size

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