Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session A12: Microfluidics I: Electrokinesis and Transport |
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Sponsoring Units: DFD Chair: Eberhard Bodenschatz, Cornell University Room: B110-B111 |
Monday, March 15, 2010 8:00AM - 8:12AM |
A12.00001: Flow Regimes and Parametric Competitions in Nanochannel Flows Chong Liu, Zhigang Li Nanoscale fluid flow systems involve both micro- and macroscopic parameters, which compete with each another and lead to different flow regimes. In this work, we investigate the competitions of four fundamental parameters, including the fluid-fluid, fluid-wall binding energies, temperature of the system, and driving force. By illustrating the fluid flux as a function of a dimensionless number, which represents the effective surface effect on the fluid, we show that the fluid motion in nanochannels falls into different regimes. For small fluid-fluid self-binding energy, there are three flow regimes; as the dimensionless number increases, the flux undergoes a transition from fluid-wall binding energy independent to temperature independent. If the fluid-wall binding energy is of the order of room temperature, there is a critical value for the dimensionless number, which divides the flow into weak and strong fluid-wall interaction regimes. Each of these regimes is associated with a distinct mechanism which reveals the competitions of the parameters. [Preview Abstract] |
Monday, March 15, 2010 8:12AM - 8:24AM |
A12.00002: Microfluidic Chemical Concentration Switching at Taylor's Limit Eberhard Bodenschatz, Albert Bae, Carsten Beta In this talk, we will discuss the time for switching chemical concentrations in microfluidic devices. The limits of rapid switching are analyzed based on the theory of dispersion by Taylor and Aris and compared to both experiments and numerical simulations. We conclude by comparing the performance of various switching techniques. [Preview Abstract] |
Monday, March 15, 2010 8:24AM - 8:36AM |
A12.00003: Film Relaxation and Pressure-Saturation Hysteresis in a Wedge-shaped Microfluidic Channel Yihong Liu, Laura Pyrak-Nolte, David Nolte Wetting-phase films play important roles in the fluid distribution and pressure-saturation behavior of porous media, but are often difficult to quantify because of their complex geometry. We used fluorescent confocal microscopy to image three-dimensional water-films in 40 $\mu $m deep wedge-shaped microfluidic channel. The microfluidic channels were fabricated from photoresist on a cover glass using two methods to achieve different wall roughness: a) two-photon laser machining, and b) UV-illumination. From the confocal images, we experimentally acquired the movement and transformation of the films and the time-dependent volume, thickness, and length of the films at controlled pressures. We also observe hysteresis in the capillary pressure vs. saturation behavior in this simple geometry when performing imbibition and drainage scanning. The wetting film, as an extension of the wetting phase, strongly increases the interaction area of the wetting phase (water) with the non-wetting phase (air) and the solid phase (channel), which contributes irreversible effects to hysteresis mechanisms. [Preview Abstract] |
Monday, March 15, 2010 8:36AM - 8:48AM |
A12.00004: Fluidic rectification due to asymmetric concentration polarization at nano-microfluidic interface Jarrod Schiffbauer, Kathleen Reschke, Boris Zaltzman, Boyd Edwards, Isaak Rubinstein, Will Booth, Aaron Timperman A simple 1D locally electroneutral (LEN) electro-diffusive model explains steady-state fluidic rectification in terms of asymmetry in the diffusion layers flanking a charge-selective element such as a porous membrane or nano-pore. The selectivity in such systems is a function of the diffusion layer asymmetry and applied voltage. Rectification is experimentally demonstrated in a microfluidic system utilizing a charge selective membrane with symmetric nanopores where the asymmetry of the diffusion layers is attributed to the geometric asymmetry in the fluidic portion of the system. Results for devices with different cross-sections on either side of the membrane verify that increasing asymmetry in the geometry, hence diffusion layers, increases the strength of the observed rectification as predicted by the theory. [Preview Abstract] |
Monday, March 15, 2010 8:48AM - 9:00AM |
A12.00005: Photo-manipulation of a liquid droplet by chromocapillary effect Arnaud Saint-Jalmes, Antoine Diguet, Reine-Marie Guillermic, Nobuyuki Magome, Kenishi Yoshikawa, Yong Chen, Damien Baigl Using simply light at different wavelengths, we show how an oil droplet floating on an aqueous solution can be trapped and rapidly moved along any desired shapes. The technique is based on the presence of a surfactant (adsorbed at the oil-water interface) which configuration and polarity change with the light wavelength. A partial illumination of the droplet, with either visible or UV light, is first used to create wavelength-dependent interfacial tension gradients, meaning that the gradient direction depends on the wavelength of the illumination. Such \textit{chromocapillary} gradients are then able to induce interfacial flows, finally resulting in reversible droplet motions in directions depending on the light wavelength. By combining ultraviolet and visible light, we then made a chromocapillary trap to capture a droplet on the liquid surface. The trapped droplet can be dragged across the surface at 300 microns per second by moving the trap around. We discuss the potential use of chromocapillary effects in microfluidic devices and in light-responsive materials. [Preview Abstract] |
Monday, March 15, 2010 9:00AM - 9:12AM |
A12.00006: Suppression of Brownian motion by electrodynamic confinement in aqueous solution Weihua Guan, Mark Reed, Sony Joseph, Predrag Krstic Trapping and manipulating single molecule or colloid particles in aqueous solution provides the opportunity to study intrinsic individual characteristics rather than averaged ensemble properties. In this study, a planar aqueous electrodynamic trap on a chip is fabricated and studied. Individual charged particles can be trapped in aqueous solution by a ``Paul trap'' type rotating electric field. The trap utilizes the strong alternating electrophoretic force and dynamically traps charged particles in the center of the planar device. The trap is characterized by investigating the stable trapping region with its characteristic driving parameters. The impact of the Brownian noise on the stability of the trapping and on the root- mean-square (rms) value of the position fluctuations are investigated. Compared to conventional Paul trap which works in vacuum or gaseous phase, our electrodynamic trap demonstrates for the first time a successful aqueous trapping. This technique opens the possibility to spatially control the object in aqueous solution and can lead to lab-on-a-chip systems controlling single molecules. [Preview Abstract] |
Monday, March 15, 2010 9:12AM - 9:24AM |
A12.00007: Two-dimensional mapping of dielectrophoresis force and AC electro-osmosis flow Jingyu Wang, H.D. Ou-Yang In an AC electric field, colloids in an aqueous suspension are subjected to different electrokinetic forces. Charged particles will experience a frequency dependent dielectrophoresis (DEP) force due to the polarizability response of the associated double layers, causing particle movement. At the cross-over frequency when the double layers cannot fully respond to the field, this force tends to zero. For free ions in solution, Coulomb forces exerted on them near the electrodes can produce fluid flows through AC-electro-osmosis (ACEO). As DEP and ACEO depend quadratically on the field strength, it is difficult to distinguish the contribution of each force exerted on a particle. To differentiate DEP and ACEO, we used optical tweezers to track individual particle motion to pin-point the DEP cross-over frequencies at locations where ACEO is negligible. We then mapped out the ACEO flow patterns at the cross-over frequency of zero DEP force. Moreover, as the cross-over frequency was a function of particle size, we were able to determine the scaling of the ACEO flow with the applied field frequency. [Preview Abstract] |
Monday, March 15, 2010 9:24AM - 9:36AM |
A12.00008: Destruction of Emulsions by an AC Electric Field: Importance of Partial Merging Abdou Rachid Thiam, Nicolas Bremond, Jer\^ome Bibette Electrocoalescence is basically the process of blending droplets by the application of an electric field. The approach is used in petroleum refineries for the separation of water in oil emulsions (that is, by coalescing water droplets), and more recently in biotechnology industry, for the fusion of micro reactors. In a first step, we will focus on the coalesce condition for two drops under a given electric field. Microfluidics offers a comfortable setup therefore, as we sought to span a range of initial conditions in terms of the distance between the droplets, their sizes, and also a region of the applied electric field. Thus, we could establish a stability diagram according to the initial conditions and droplets' composition, which displays three domains referred to as: coalescence, no coalescence and a third one of partial coalescence, where the droplets coalesce for a brief moment then separate right afterwards. We proceeded then by generalizing the setup to the case of a stream of droplets, and we found that the evolution of the stream can be predicted by the behaviour of the local pairs of droplets, as seen in the previous step. The main outcome of that study is the total destruction of an emulsion above a critical volume fraction for a given amplitude of electric field. [Preview Abstract] |
Monday, March 15, 2010 9:36AM - 9:48AM |
A12.00009: Broadband Dielectric Response of Insulin and Bovine Serum Albumin in Solution J. Booth, N. Orloff, Y. Wang, J. Dennis, I. Takeuchi We report on quantitative frequency-dependent permittivity measurements of nanoliter volumes of bovine serum albumin and insulin in solution, using microfluidic channels integrated with planar microwave frequency transmission lines. Our measurements yield quantitative values for the solution permittivity as a function of frequency for different values of protein concentration, over the broad freqeuncy range 45 MHz to 40 GHz. Analysis of these data based on dielectric mixing models allows us to extract quantitative values for the effective molecular permittivity of the aqueous proteins, as a function of frequency. [Preview Abstract] |
Monday, March 15, 2010 9:48AM - 10:00AM |
A12.00010: Single-Molecule Denaturation Mapping of DNA in Nanofluidic Channels Walter Reisner, Niels Larsen, Asli Silahtaroglu, Anders Kristensen, Niels Tommerup, Jonas O. Tegenfeldt, Henrik Flyvbjerg Nanochannel based DNA stretching can serve as a platform for a new optical mapping technique based on measuring the pattern of partial melting along the extended molecules. We partially melt DNA extended in nanofluidic channels via a combination of local heating and added chemical denaturants. The melted molecules, imaged via a standard fluorescence videomicroscopy setup, exhibit a nonuniform fluorescence profile corresponding to a series of local dips and peaks in the intensity trace along the stretched molecule. We show that this barcode is consistent with the presence of locally melted regions along the molecule and can be explained by calculations of sequence-dependent melting probability. Specifically, we obtain experimental melting profiles for T4, T7, lambda-phage and bacterial artificial chromosome DNA (from human chromosome 12) and compare these profiles to theory. In addition, we demonstrate that the BAC melting profile can be used to align the BAC to its correct position on chromosome 12. [Preview Abstract] |
Monday, March 15, 2010 10:00AM - 10:12AM |
A12.00011: Channeling of DNA during Electrophoresis in a Sparse Ordered Post Array Jia Ou, Jaseol Cho, Sam Carpenter, Dan Olson, Kevin Dorfman Microfabricated post arrays are a promising approach to separate long DNA by size. Simulation data suggest that, if the post array is ordered and sparse, then long DNA will move through the array with very few collisions and the separation will be lost. We tested this ``channeling hypothesis'' using 1 $\mu$m diameter post arrays with two different pitches: 3 $\mu$m and 7 $\mu$m. The mobility, dispersivity and videomicroscopy data for $\lambda$-DNA in a 3$\mu$m pitch array indicate that the DNA frequently collide with the posts over a wide range of electric fields. We demonstrate via simulations that the frequent collisions are due to the curved electric field lines. To detect the onset of channeling in the 7$\mu$m pitch array, which has a more uniform field, we compared the electrophoretic mobility of $\lambda$-DNA and a smaller plasmid, pUC19 (2,383 bp), that cannot make a rope-over-pulley collision. At low electric fields, these DNA are separated because the $\lambda$-DNA collides with the posts. The resolution is lost as the electric field increases due to the onset of channeling by the $\lambda$-DNA. [Preview Abstract] |
Monday, March 15, 2010 10:12AM - 10:24AM |
A12.00012: DNA mobility in nanofluidic systems Alena Karpusenko, Shuang Fang Lim, Robert Riehn Nano-scale devices are attractive candidates for rapid and inexpensive biological analysis. Particular focus has been the analysis of DNA, studied in both nano-pores and nanofluidic channels. DNA is linearized and stretched to about 60 \% of its contour length by confinement to channels with a cross-section of 100$\times$100 nm$^2$ and hundreds of microns long. Here we study the motion of dsDNA through mazes of nanofluidic channels, and in particular the dependence of average drift velocities on the size and shape of the molecules. We find interesting relationships by comparing the average displacement for different molecules when driven by electric fields. We propose separation techniques for DNA molecules with different topologies using specific fluidic systems and driving schemes. [Preview Abstract] |
Monday, March 15, 2010 10:24AM - 10:36AM |
A12.00013: Tube-like motion of ds-DNA in a nanoslit post array Po-Keng Lin, Chen-Hsiang Hung, Chia-Fu Chou, Yeng-Long Chen Polymer reptation motion has been observed in polymer trapped in a porous network with pore size smaller than the chain Kuhn length. In this study, we directly observe the tube-like motion of DNA confined in nano-height hexagonal micropost arrays, where the post spacing is much larger than the Kuhn length. The chain length $N $dependence of DNA diffusivity $D$ exhibits the two-dimensional reptation scaling D $\sim \quad N^{-1.5}$. The tube-like motion results from confinement-induced attraction between DNA and the microposts. We also systematically investigate the transition of DNA-wall interaction from repulsion to attraction. [Preview Abstract] |
Monday, March 15, 2010 10:36AM - 10:48AM |
A12.00014: Bubble length affects bubble speed in a rough microfluidic channel Quan Zhang, Konstantin Turitsyn, Tom Witten We discuss the creeping motion of bubbles of different length in rough capillary tubes filled with carrier fluids. This extends the results of Bretherton\footnote{F.P.Bretherton, 1961, J. Fluid Mech., 10, 166.} for an infinite-length bubble at small capillary number $Ca$ in a circular tube. We first derive the asymptotic corrections to the speed owing to finite length. This dependence on length is exponentially small, with a decay length much shorter than the tube radius $R$. Then we discuss the effect of azimuthal roughness of the tube on the bubble speed. Tube roughness leads to a carrier fluid flow in the azimuthal plane; this flow controls the relaxation of the bubble shape to its infinite length limit. For long-wavelength roughness, we find that the above decay length becomes much longer and even comparable to $R$. This implies a much-enhanced dependence of the bubble velocity on length. A shorter bubble should then catch up with a longer bubble ahead of it in the same channel. This mechanism may explain catch-up effects seen experimentally.\footnote{R.Ismagilov, private communication.} [Preview Abstract] |
Monday, March 15, 2010 10:48AM - 11:00AM |
A12.00015: Vesicle extrusion in nanopores B\'ela Jo\'os, Martin Bertrand, S\'ebastien Ouellet Monodisperse vesicles of nearly circular shape or liposomes are used as drug delivery systems. Their fabrication involves repeated passage of large vesicles through small pores. At each passage the vesicle ruptures and the fragments reform into smaller vesicles. We report on the last stages of the process where small liposomes are pushed by pressure differences into nano-sized pores, and we study the stress distribution along the lipid bilayer to determine the rupture lines. This is done by performing coarse grained Molecular Dynamics simulations. We have developed a technique to measure the stress in the membrane based on a tessellation of the surface which allows us to monitor the local area per lipid fluctuations. The results show subtle and complex flow phenomena. We can predict the final size distribution after many passages. Comparisons will be made with existing experimental data. [Preview Abstract] |
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