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IMA Newsletter #398

December 2009

2009-2010 Program

See http://www.ima.umn.edu/2009-2010/ for a full description of the 2009-2010 program on Complex Fluids and Complex Flows.

News and Notes

IMA Events

IMA Tutorial

Mathematics of Microfluidic Transport Phenomena

December 5-6, 2009

Organizers: Martin Z. Bazant (Massachusetts Institute of Technology), Sandip Ghosal (Northwestern University), Susan J. Muller (University of California), Ali Nadim (Claremont Graduate University), Todd Squires (University of California)

IMA Annual Program Year Workshop

Microfluidics: Electrokinetic and Interfacial Phenomena

December 7-11, 2009

Organizers: Martin Z. Bazant (Massachusetts Institute of Technology), Sandip Ghosal (Northwestern University), Susan J. Muller (University of California), Ali Nadim (Claremont Graduate University), Todd Squires (University of California)
Schedule

Tuesday, December 1

10:45am-11:15amCoffee breakLind Hall 400
11:15am-12:15pmVariational representations, small noise large deviations and applicationsVasileios Maroulas (University of Minnesota)Lind Hall 305 PS

Wednesday, December 2

10:45am-11:15amCoffee breakLind Hall 400
2:30pm-3:20pmTopics in the theory of the Navier-Stokes equationsVladimir Sverak (University of Minnesota)Lind Hall 305

Thursday, December 3

10:45am-11:15amCoffee breakLind Hall 400

Friday, December 4

10:45am-11:15amCoffee breakLind Hall 400
1:25pm-2:25pm Laser ribbon bond loop shape prediction and optimization J. Michael Gray (Medtronic)Vincent Hall 570 IPS

Saturday, December 5

8:15am-8:45amRegistration and coffeeEE/CS 3-176 T12.5-6.09
8:45am-9:00amWelcome to the IMAFadil Santosa (University of Minnesota)EE/CS 3-180 T12.5-6.09
9:00am-10:30amElectrokinetics of highly charged surfaces Todd Squires (University of California, Santa Barbara)EE/CS 3-180 T12.5-6.09
10:30am-10:45amCoffee breakEE/CS 3-176 T12.5-6.09
10:45am-12:15pmElectrokinetic phenomena in particulate suspensions: an introductionDavid Saintillan (University of Illinois at Urbana-Champaign)EE/CS 3-180 T12.5-6.09
12:15pm-2:00pmLunch T12.5-6.09
2:00pm-3:30pmElectroosmotic flow and dispersion in microfluidicsSandip Ghosal (Northwestern University)EE/CS 3-180 T12.5-6.09
3:30pm-4:00pmCoffee breakEE/CS 3-176 T12.5-6.09
4:00pm-5:30pmElectric double layer and concentration polarizationBoris Zaltzman (Jacob Blaustein Institute for Desert Research)EE/CS 3-180 T12.5-6.09

Sunday, December 6

8:30am-9:00amCoffeeEE/CS 3-176 T12.5-6.09
9:00am-10:30amElectrowetting and digital microfluidicsAli Nadim (Claremont Graduate University)EE/CS 3-180 T12.5-6.09
10:30am-10:45amCoffee breakEE/CS 3-176 T12.5-6.09
10:45am-12:15pmConfinement effects with macromoleculesSusan J. Muller (University of California, Berkeley)EE/CS 3-180 T12.5-6.09
12:15pm-2:00pmLunch T12.5-6.09
2:00pm-3:30pmAn Introduction to interfaces and multiphase flows in microfluidicsShelley L. Anna (Carnegie Mellon University)EE/CS 3-180 T12.5-6.09
3:30pm-4:00pmCoffee breakEE/CS 3-176 T12.5-6.09
4:00pm-5:30pmInduced-charge electrokinetics Martin Z. Bazant (Massachusetts Institute of Technology)EE/CS 3-180 T12.5-6.09

Monday, December 7

All DayChair: Sandip Ghosal (Northwestern, University) W12.7-11.09
8:15am-8:45amRegistration and coffeeEE/CS 3-176 W12.7-11.09
8:45am-9:00amWelcome to the IMAFadil Santosa (University of Minnesota)EE/CS 3-180 W12.7-11.09
9:00am-9:40amProgrammable soft matterManu Prakash (Harvard University)EE/CS 3-180 W12.7-11.09
9:40am-10:20amDNA electrophoresis in microfabricated arraysKevin D. Dorfman (University of Minnesota)EE/CS 3-180 W12.7-11.09
10:20am-10:50amCoffee breakEE/CS 3-176 W12.7-11.09
10:50am-11:30amElectrokinetics in planar nanofluidic channelsSumita Pennathur (University of California, Santa Barbara)EE/CS 3-180 W12.7-11.09
11:30am-1:30pmLunch W12.7-11.09
1:30pm-2:10pmWetting of structured substrates and flexible membranes Reinhard Lipowsky (Max Planck Institute for Colloids and Interfaces)EE/CS 3-180 W12.7-11.09
2:10pm-2:50pmMixing and internal flows in drops in AC electrowettingFrieder Mugele (Universiteit Twente)EE/CS 3-180 W12.7-11.09
2:50pm-3:00pmGroup Photo W12.7-11.09
3:00pm-3:30pmCoffee breakEE/CS 3-176 W12.7-11.09
3:30pm-4:00pmSecond chancesEE/CS 3-180 W12.7-11.09
4:00pm-6:00pmReception and Poster Session
Poster submissions welcome from all participants
Instructions
Lind Hall 400 W12.7-11.09
Numerical simulations of dynamic wettingShahriar Afkhami (New Jersey Institute of Technology)
Particle separation by capillary electrophoresis in nanochannelsPaul J. Atzberger ()
Strongly nonlinear dynamics of electrolytes in large ac voltagesHenrik Bruus (Technical University of Denmark)
Non-monotonic energy dissipation in microfluidic cantilever resonatorsThomas P. Burg (Max-Planck-Institut für Biophysikalische Chemie)
Capillary-driven thin-film flows on stationary and periodically-stretched substrates having isolated topographic features Greg P. Chini (University of New Hampshire)
Enhancement of charged macromolecule capture by nanopores in a salt gradient Tom Chou (University of California, Los Angeles)
Micro and nanoscale transport of biomolecules through poresA. Terrence Conlisk (Ohio State University)
Speed of KPP fronts with a cut-off: rigorous resultsM. Cristina Depassier (Pontificia Universidad Catolica de Chile)
Two-phase flow diffuse interface models for dynamic electrowettingMarco Antonio Fontelos (Consejo Superior de Investigaciones Científicas (CSIC))
Günther Grün (Friedrich-Alexander-Universität Erlangen-Nürnberg)
Dielectrophoretic deflection and rebound of continuous droplet streamsThomas B. Jones (University of Rochester)
Interfacial dynamics of colloidal particles in electrokinetically driven flows measured by multilayer nano-particle image velocimetry (MnPIV)Yutaka Kazoe (Georgia Institute of Technology)
Influence of ion sterics and hydrodynamic slip on electrophoresis of a colloidal particleAditya Satish Khair (University of California, Santa Barbara)
Stretch dependency of the electrophoretic mobility of DNARonald G. Larson (University of Michigan)
Wetting transition, drop impact, and microfow on hydrophobic microstructuresDetlef Lohse (Universiteit Twente)
A fluid mechanical origin of sheet ejection during droplet impacting a dry surfaceShreyas Mandre (Harvard University)
Surface charge measurement and control by gate voltage in electroosmotic flow Frieder Mugele (Universiteit Twente)
High order quadratures for the evaluation of interfacial velocities in axi-symmetric Stokes flows Monika Nitsche (University of New Mexico)
Locomotion of synthetic nanomotorsJonathan D. Posner (Arizona State University)
Traveling-wave electroosmosis and faradaic currents: the diffusion layerAntonio Ramos (University of Sevilla)
Multi-physics computational models for neuro-chip simulationRiccardo Sacco (Politecnico di Milano)
Hydrodynamic trap for single cells, particles and moleculesCharles M. Schroeder (University of Illinois at Urbana-Champaign)
Free energy landscaping: Nanotopographic control over DNA conformations and transportDerek Stein (Brown University)
A diffusive interface method of modeling mutli-phase flows Huan Sun (Pennsylvania State University)
Electric field gradient focusing in microchannels with embedded bipolar electrode Ulrich Tallarek (Philipps-Universität Marburg)
Dynamics of drops and vesicles in electric fieldsPetia M. Vlahovska (Dartmouth College)
Understanding electrokinetics at the nanoscale: Beyond the limiting currentGilad Yossifon (Technion-Israel Institute of Technology)

Tuesday, December 8

All DayChair: Martin Z. Bazant (Massachusetts Institute of Technology) W12.7-11.09
8:30am-9:00amCoffeeEE/CS 3-176 W12.7-11.09
9:00am-9:40amMigration of ion-exchange particles under the action of a uniformly applied electric fieldEhud Yariv (Technion-Israel Institute of Technology)EE/CS 3-180 W12.7-11.09
9:40am-10:20amMaking small thingsJens Eggers (University of Bristol)EE/CS 3-180 W12.7-11.09
10:20am-10:50amCoffee breakEE/CS 3-176 W12.7-11.09
10:50am-11:30amThe microfluidics of colloidal particle-vesicle-capsule mixtures with application to blood additivesEric S. G. Shaqfeh (Stanford University)EE/CS 3-180 W12.7-11.09
11:30am-1:30pmLunch W12.7-11.09
1:30pm-2:10pmDNA dynamics in confinement and complex electric fieldsPatrick S. Doyle (Massachusetts Institute of Technology)EE/CS 3-180 W12.7-11.09
2:10pm-2:50pm Nonuniform interfacial colloidal tracer distributions and implications for microscale PIVMinami Yoda (Georgia Institute of Technology)EE/CS 3-180 W12.7-11.09
2:50pm-3:20pmCoffee breakEE/CS 3-176 W12.7-11.09
3:20pm-4:00pmNematic liquid crystals in thin geometriesLinda J. Cummings (New Jersey Institute of Technology)EE/CS 3-180 W12.7-11.09
4:00pm-4:30pmSecond chancesEE/CS 3-180 W12.7-11.09

Wednesday, December 9

All DayChair: Todd Squires (University of California, Santa Barbara) W12.7-11.09
8:30am-9:00amCoffeeEE/CS 3-176 W12.7-11.09
9:00am-9:40amImpact figuresDavid Quéré (École Supérieure de Physique et de Chimie Industrielles de la Ville de Paris (ESPCI))EE/CS 3-180 W12.7-11.09
9:40am-10:20amHydrodynamics challenges in inkjet printing Detlef Lohse (Universiteit Twente)EE/CS 3-180 W12.7-11.09
10:20am-10:50amCoffee breakEE/CS 3-176 W12.7-11.09
10:50am-11:30amThe electromechanics of liquidsThomas B. Jones (University of Rochester)EE/CS 3-180 W12.7-11.09
11:30am-1:30pmLunch W12.7-11.09
1:30pm-2:10pmDynamics of lipid bilayer membranesMichael J. Miksis (Northwestern University)EE/CS 3-180 W12.7-11.09
2:10pm-2:50pmEnergetic variational approaches in calcium and sodium channelsChun Liu (University of Minnesota)EE/CS 3-180 W12.7-11.09
2:50pm-3:20pmCoffee breakEE/CS 3-176 W12.7-11.09
3:20pm-4:00pmElectrokinetic ion transport and liquid flux across nanochannelsHsueh-Chia Chang (University of Notre Dame)EE/CS 3-180 W12.7-11.09
4:00pm-4:30pmSecond chancesEE/CS 3-180 W12.7-11.09

Thursday, December 10

All DayChair: Ali Nadim (Claremont Graduate University) W12.7-11.09
8:30am-9:00amCoffeeEE/CS 3-176 W12.7-11.09
9:00am-9:40amElectrical streaming potential generated by 2-phase flow John D. Sherwood (University of Cambridge)EE/CS 3-180 W12.7-11.09
9:40am-10:20amVesicles and red blood cells under shear and Poiseuille flowChaouqi Misbah (Université de Grenoble I (Joseph Fourier))EE/CS 3-180 W12.7-11.09
10:20am-10:50amCoffee breakEE/CS 3-176 W12.7-11.09
10:50am-11:30amCountering capillarity with electrokinetics: from micro-manipulation to Debye-layer diagnostics Paul H. Steen (Cornell University)EE/CS 3-180 W12.7-11.09
11:30am-1:30pmLunch W12.7-11.09
1:30pm-2:10pmExtended space charge effects in concentration polarization Isaak Rubinstein (Ben Gurion University of the Negev)EE/CS 3-180 W12.7-11.09
2:10pm-2:40pmCoffee breakEE/CS 3-176 W12.7-11.09
2:40pm-3:20pmAdventures in self assemblyMichael P. Brenner (Harvard University)EE/CS 3-180 W12.7-11.09
3:20pm-3:50pmSecond chancesEE/CS 3-180 W12.7-11.09
6:30pm-8:30pmWorkshop Dinner at Caspian BistroCaspian Bistro
2418 University Ave SE
Minneapolis, MN 55414
612-623-1133
W12.7-11.09

Friday, December 11

All DayChair: Susan J. Muller (University of California, Berkeley) W12.7-11.09
8:30am-9:00amCoffeeEE/CS 3-176 W12.7-11.09
9:00am-9:40amScaling arguments for tipstreaming of submicron dropletsShelley L. Anna (Carnegie Mellon University)EE/CS 3-180 W12.7-11.09
9:40am-10:20amIon transport through nanopores: From living cells to diodes and transistors Zuzanna S. Siwy (University of California, Irvine)EE/CS 3-180 W12.7-11.09
10:20am-10:50amCoffee breakEE/CS 3-176 W12.7-11.09
10:50am-11:30amThe influence of boundaries on shear banding in complex fluids Peter D. Olmsted (University of Leeds)EE/CS 3-180 W12.7-11.09
11:30am-12:00pmSecond chances/closing remarksEE/CS 3-176 W12.7-11.09

Monday, December 14

2:30pm-3:20pmTopics in the theory of the Navier-Stokes equations Vladimir Sverak (University of Minnesota)Lind Hall 305

Tuesday, December 15

11:15am-12:15pmThe optimal size for space discretization in spatially nonuniform reaction-diffusion systemsHye-Won Kang (University of Minnesota)Lind Hall 305 PS

Wednesday, December 16

2:30pm-3:20pmTopics in the theory of the Navier-Stokes equations Vladimir Sverak (University of Minnesota)Lind Hall 305

Friday, December 18

1:25pm-2:25pmResearch in applied mathematics at SchlumbergerLalitha Venkataramanan (Schlumberger-Doll)Vincent Hall 570 IPS

Thursday, December 24

All DayFloating holiday. The IMA is closed.

Friday, December 25

All DayChristmas Day. The IMA is closed.
Abstracts
Second chances
Abstract: No Abstract
Second chances
Abstract: No Abstract
Second chances
Abstract: No Abstract
Second chances
Abstract: No Abstract
Second chances/closing remarks
Abstract: No Abstract
Shahriar Afkhami (New Jersey Institute of Technology) Numerical simulations of dynamic wetting
Abstract: With miniaturization of fluidic devices, small-scale effects such as the details of the flow near the contact line become important. We present a three-dimensional numerical model to simulate the dynamic behavior of moving contact line phenomena. The model consists of an adaptive mesh discretization of the time-dependent Navier-Stokes equations for incompressible two-phase flows with a volume-of-fluid technique for interface tracking. Equilibrium results of three-dimensional droplets with various contact angles are presented and compared with known solutions. The slip of a moving contact line on the solid surface and the dynamical contact angle are computationally investigated. Some numerical simulations of the model applied to electrowetting are presented.
Shelley L. Anna (Carnegie Mellon University) An Introduction to interfaces and multiphase flows in microfluidics
Abstract: No Abstract
Shelley L. Anna (Carnegie Mellon University) Scaling arguments for tipstreaming of submicron droplets
Abstract: Microfluidic devices are convenient for producing highly uniform droplets for precise emulsions and lab-on-a-chip devices. However, the minimum droplet size in a microfluidic process is determined by the smallest geometric feature size, typically on the order of tens of microns. Introducing additional physico-chemical effects can help overcome this fundamental limitation. For example, when dissolved surfactants are present in one of the liquid phases, a tipstreaming-like phenomenon occurs, leading to the formation of submicron droplets. We have characterized this phenomenon in detail as a function of fluid properties and flow kinematics. However, we still have only a phenomenological understanding of the role of surfactant in the tipstreaming process. Experiments and recent literature suggest that the adsorption and desorption of surfactants at the interface plays an important role. In this talk, we demonstrate the feasibility of this hypothesis via scaling arguments for the diffusion, adsorption, and desorption of soluble surfactants in micron-scale geometries.
Paul J. Atzberger Particle separation by capillary electrophoresis in nanochannels
Abstract: We discuss an on-going theoretical / experimental effort studying particle separation through capillary electropohoresis in nanochannels. Recent experimental results in the laboratory of Dr. Pennathur (UCSB, Dept. ME) indicate that increased fidelity in separating particles by size and charge can be achieved when using channels with cross sections of nanometer dimensions (100nm x 1000nm) as opposed to larger microchannels. For short double-strands of DNA (10 - 100 base pairs) it is found that separation in free solution produces only one lumped peak in the fluorescence signal for microchannels but several clearly distinct peaks in nanochannels. Many effects which are weak in microchannels are expected to play a strong role in nanochannels owing to the large surface area to volume ratio and steric restrictions imposed on particle configurations. Models are presented for separation which investigate the role of the particle-particle and particle-wall steric interactions, the hydrodynamic flow and coupling, the overlap of double layers, and the translational and rotational diffusion of particles. This work is also being carried out with Dr. Gibou (UCSB, Dept. ME) and with the graduate student David Boy.
Martin Z. Bazant (Massachusetts Institute of Technology) Induced-charge electrokinetics
Abstract: No Abstract
Michael P. Brenner (Harvard University) Adventures in self assembly
Abstract: Self assembly is the idea of creating a system whose component parts spontaneously assemble into a structure of interest. In this talk I will outline our research program aimed at creating self-assembled structures out of very small spheres, that bind to each other on sticking. The talk will focus on (i) some fundamental mathematical questions in finite sphere packings (e.g. how do the number of rigid packings grow with N, the number of spheres); (ii) algorithms for self assembly (e.g. suppose the spheres are not identical, so that every sphere does not stick to every other; how to design the system to promote particular structures); (iii) physical questions (e.g. what is the probability that a given packing with N particles forms for a system of colloidal nanospheres); (iv) comparisons with experiments on colloidal nanospheres. and (v) ways of using microfluidics to enable kinetically driven self assembly.
Henrik Bruus (Technical University of Denmark) Strongly nonlinear dynamics of electrolytes in large ac voltages
Abstract: Preprint (ArXiv) We study the response of a model micro-electrochemical cell to a large ac voltage of frequency comparable to the inverse cell relaxation time. To bring out the basic physics, we consider the simplest possible model of a symmetric binary electrolyte confined between parallel-plate blocking electrodes, ignoring any transverse instability or fluid flow.

We analyze the resulting one-dimensional problem by matched asymptotic expansions in the limit of thin double layers and extend previous work into the strongly nonlinear regime, which is characterized by two novel features (1) significant salt depletion in the electrolyte near the electrodes and (2), at very large voltage, the breakdown of the quasi-equilibrium structure of the double layers. The former leads to the prediction of "ac capacitive desalination", since there is a time-averaged transfer of salt from the bulk to the double layers, via oscillating diffusion layers. The latter is associated with transient diffusion limitation, which drives the formation and collapse of space-charge layers, even in the absence of any net Faradaic current through the cell.

We also predict that steric effects of finite ion sizes (going beyond dilute solution theory) act to suppress the strongly nonlinear regime in the limit of concentrated electrolytes, ionic liquids and molten salts. Beyond the model problem, our reduced equations for thin double layers, based on uniformly valid matched asymptotic expansions, provide a useful mathematical framework to describe additional nonlinear responses to large ac voltages, such as Faradaic reactions, electro-osmotic instabilities, and induced-charge electrokinetic phenomena.

Thomas P. Burg (Max-Planck-Institut für Biophysikalische Chemie) Non-monotonic energy dissipation in microfluidic cantilever resonators
Abstract: Nanomechanical resonators enable a range of precision measurements in air or vacuum, but strong viscous damping makes applications in liquid challenging. Recent experiments have shown that fluid damping can be greatly reduced by confining the sample to a fluidic channel embedded inside the resonator while the outside is under vacuum. Understanding fluid damping in such systems is critical for future applications to problems spanning a wide range of scales in nanoscience and biology. Measurements presented here reveal that energy dissipation in cantilevers with embedded fluidic channels is a non-monotonic function of viscosity, suggesting that the quality factor may actually be enhanced through miniaturization. These results are found to be consistent with a first-order hydrodynamic model of the fluid-filled vibrating cantilever beam. In the regime of low-viscosity, inertia dominates the fluid motion inside the cantilever, resulting in thin viscous boundary layers - this leads to an increase in energy dissipation with increasing viscosity. In the high-viscosity regime, the boundary layers on all surfaces merge, leading to a decrease in dissipation with increasing viscosity. Effects of fluid compressibility also become significant in this latter regime and lead to rich flow behaviour. Based on these results, we anticipate that scaling of current devices by more than ten-fold may be possible without significant degradation of the quality factor due to damping induced by the fluid.
Hsueh-Chia Chang (University of Notre Dame) Electrokinetic ion transport and liquid flux across nanochannels
Abstract: Keywords: electrokinetics, nanoscience, limiting current, Donnan potential, ion selectivity, Warburg Impedance Abstract: With the advent of nanofabrication technologies, nano-channels with dimensions smaller than the Debye screening layer can now be fabricated to allow scrutiny of the various anomalous DC and AC I-V characteristics of ion-selective membranes at the single-pore level — such knowledge is essential for rapid DNA sequencing, single-molecule sensing/identification and plasmonic imaging in nanoscience. Combining theoretical analyses of the underlying ion/solvent fluxes and confocal imaging of velocity and ion concentration fields, we explore the fundamental mechanisms behind non-ideal selectivity, Donnan potential, asymmetric depletion/enrichment layer formation, limiting and overlimiting-current, diode-like rectification, Warburg impedance response, inter-channel communication etc. Curiously, hydrodynamic effects at the depletion end of the channel is found to control many of the non-Ohmic behavior at higher voltages. Interfacial vortices created by an osmotic pressure driven instability (first predicted by I. Rubinstein) and induced charges at the corners of nanopores are found to specify the overlimiting current, the rectification factor and inter-pore communication. The intensity of these vortices and their influence on the ion-carried currents are found to be strongly dependent on the pore/reservoir geometries and can be described by limiting fundamental solutions of the Laplace and Stokes equations due to severe electric and flow field focusing into the nanochannel.
Greg P. Chini (University of New Hampshire) Capillary-driven thin-film flows on stationary and periodically-stretched substrates having isolated topographic features
Abstract: The capillary-driven readjustment of thin liquid films subject to sudden, localized changes in shape or to periodic stretching of adjacent solid surfaces is important in a variety of industrial and physiological flow configurations. To investigate this process, we perform a combination of finite-difference numerical simulations and matched and multiple-scale asymptotic analyses of several related, simplified models. Thin films readjusting near isolated interior corners or "large" humps generically attain an intermediate-asymptotic state consisting of a corner puddle, a "Jones--Wilson" (or "Hammond") draining region, through which fluid slowly drains into the puddle, and a far-field, propagating capillary wave. (For thin-film flows near "small" humps, the capillary wave attaches directly to the hump.) In the presence of distant lateral no-flux boundaries, the thin film ultimately reaches a quasi-steady configuration consisting of a droplet, a Jones--Wilson draining region, and a corner puddle, as has long been known. This quasi-steady film distribution is dramatically altered by the introduction of prescribed substrate stretching. At low frequencies, the pressure distribution becomes non-monotonic and the drainage region is rendered passive. A "Bretherton" region, which connects the corner puddle to a wedge-like region emerges, and drag-out and drag-in profiles are asymmetric. At high frequencies, the effects of the pressure oscillation are screened in a small neighborhood of the corner. This work is motivated by applications in pulmonary alveolar mechanics.
Tom Chou (University of California, Los Angeles) Enhancement of charged macromolecule capture by nanopores in a salt gradient
Abstract: An theoretical analysis is performed to explain recently observations that salt gradients across a nanopore can increase charged analyte capture rates.
A. Terrence Conlisk (Ohio State University) Micro and nanoscale transport of biomolecules through pores
Abstract: Computational and theoretical models are developed for the transport of biomolecules and electrostatic and electrokinetic phenomena in nanopore membranes. For the application of nanopore sequencing, the electrophoretic transport of double stranded DNA molecules through a converging nanopore is investigated. The forces that affect the DNA translocation are analyzed and the DNA translocation velocity is predicted. The computational model is validated by good agreement between the computational results and the experimental data. Motivated by the design requirements for a hemofilter in an implantable artificial kidney, the hindered transport of biomolecules through a nanopore membrane is studied, particularly for the selectivity of the charged membrane to charged biomolecules of biological interest, particularly human serum albumin. The developed theory is applied to the problem of choosing a hemofilter pore size that provides adequate retention/clearance of desirable/undesirable solutes from blood.
Linda J. Cummings (New Jersey Institute of Technology) Nematic liquid crystals in thin geometries
Abstract: Keywords: Nematic Liquid Crystal, non-Newtonian, lubrication theory, asymptotics, electric field effects, interfacial instability, free boundary problem, LCD Abstract: Nematic liquid crystals are materials intermediate between the liquid and solid states. They are typically composed of long, rod-like molecules, which have a tendency to align with their neighbors, imparting a short-range (but no long-range) orientational order - although nematics flow, like conventional liquids, they also retain some elastic character. This gives rise to complex behavior that does not arise in Newtonian liquids. Moreover, their response to an applied electric field gives nematics wide application in the electronic display industry. We consider mathematical models for three different problems. Two are classical fluid-dynamical setups: a small droplet spreading on a flat substrate; and a two-dimensional "liquid bridge" (or liquid sheet) under tension. These are free boundary problems, and the thin geometry in each case enables the use of "lubrication" analysis to systematically derive reduced mathematical models governing the free surface evolution. The spreading drop analysis leads to variants of the classical 4th order "thin film" equation, which can exhibit instability in certain regimes. The "liquid bridge" problem leads to new versions of the so-called Trouton model for Newtonian viscous sheets. The third problem arises in the display industry, and is concerned with manufacturing a "bistable" display device, that can exhibit two optically-distinct configurations in the absence of an electric field. Such a device has the potential for considerably reducing the power demands of a display, with accompanying benefits for battery lifetime and device portability.
M. Cristina Depassier (Pontificia Universidad Catolica de Chile) Speed of KPP fronts with a cut-off: rigorous results
Abstract: We study the reaction diffusion equation ut = uxx + f(u), with a cut-off ε in the reaction term. The reaction term without a cut-off is assumed to be of KPP type. The introduction of the cut-off on the reaction term has been shown to model the effect of noise and the finiteness of the number of diffusing particles. Rigorous bounds on the speed are given for arbitrary values of ε. For small cut-off the Brunet-Derrida value is recovered, the bounds from allow to determine its range of validity. In the opposite limit of large cut-off the speed tends to zero as the square root of (1-ε). The results are obtained making use of a variational characterization of the speed.
Kevin D. Dorfman (University of Minnesota) DNA electrophoresis in microfabricated arrays
Abstract: Keywords: Brownian dynamics, microfabrication, boundary element method, DNA electrophoresis, separations Abstract: I will present our recent results on the dynamics of long DNA as they move through a hexagonal arrays of microfabricated posts under the influence of an electric field. The first part of the talk focuses on the potential of using sparse, ordered post arrays to separate long DNA by molecular weight. In particular, I will focus on the crucial role of electric field gradients on the separation process and how we can use microfabrication tools to control these gradients. In the second part of the talk, I will demonstrate how we are using a combination of Brownian dynamics simulations and videomicroscopy to gain a detailed understanding of the separation process at the macromolecular level.
Patrick S. Doyle (Massachusetts Institute of Technology) DNA dynamics in confinement and complex electric fields
Abstract: Keywords: DNA, microfluidic, nanofluidic, electrophoresis Abstract: Large double stranded DNA are both a powerful system to study polymer dynamics at the single molecule level and also important molecules for genomic applications. While homogenous electric fields are routinely used to separate DNA in gels, DNA deformation in more complex fields has been less widely studied. We will demonstrate how micro/nanofluidic devices allow for the generation of electric fields with well-defined kinematics for trapping, stretching and then watching DNA relax back to equilibrium. The dimensions of the devices highly confine DNA and subsequently change both their conformation and dynamics. First, I will discuss how confinement changes the conformational relaxation time and introduces new relaxation regimes not seen in bulk. Next, I will show how these confinements effects change the coil-stretch transition of a DNA being electrophoretically stretched in a purely elongational electrical field.
Jens Eggers (University of Bristol) Making small things
Abstract: Keywords: Singularities, Free surface flows Abstract: Viscous flow is extremely effective in deforming a free surface into very sharp features such as tips or cups. Under increased driving such free surface singularities may turn unstable, and give way to secondary structures. In particular, this may be turned into a method to "manufacture" small things by using the nonlinear character of the equations of hydrodynamics.
Marco Antonio Fontelos (Consejo Superior de Investigaciones Científicas (CSIC)), Günther Grün (Friedrich-Alexander-Universität Erlangen-Nürnberg) Two-phase flow diffuse interface models for dynamic electrowetting
Abstract: We present thermodynamically consistent models for dynamic electrowetting and other electrokinetic phenomena involving conductive liquids or electrolyte solutions. They combine Navier-Stokes equations, evolution equations for ion/charge densities and for phase field with an elliptic transmission problem forthe electrostatic potential. We provide numerical and theoretical argumentsi ndicating that microscopically Young's contact angle persists in equilibrium configurations. Moreover, the models allow for contact-angle hysteresis. In addition, 2D and 3D numerical simulations on electric field induced droplet motion are presented. Finally, rigorous mathematical analysis shows global-in-time existence of solutions to the models under consideration.
Sandip Ghosal (Northwestern University) Electroosmotic flow and dispersion in microfluidics
Abstract: No Abstract
Thomas B. Jones (University of Rochester) The electromechanics of liquids
Abstract: Keywords: dielectrophoresis, electrowetting, electromechanics, microfluidics Abstract: When subjected to electric fields, liquids exhibit a large range of dynamic and kinematic phenomena. This lecture focuses on the liquid electromechanical effects commonly exploited to dispense, move, and manipulate small liquid masses (including droplets) in microfluidic applications. Irrespective of the fine details, the net, observable force interaction very often can be predicted in terms of an appealingly simple, lumped parameter model. In particular, as long as the capacitance of a microfluidic structure can be expressed in terms of a small number of mechanical variables that adequately describe liquid displacement and distortion, then an electromechanical system model is born. Because such models can describe the important fluid behavior of insulating and conductive liquids, microfluidic schemes based on either liquid dielectrophoresis, electrowetting-on-dielectric, or a combination of the two can be treated. The lumped parameter approach avoids issues associated with volume force densities and often circumvents the need for numerical electric field computations.
Thomas B. Jones (University of Rochester) Dielectrophoretic deflection and rebound of continuous droplet streams
Abstract: Joint work with Paul Chiarot (Department of Electrical and Computer Engineering, University of Rochester). In continuous ink jet systems, streams of ~10 picoliter liquid droplets (diameter ~30 microns) are ejected from an array of orifices at rates of up to 350,000 per second and velocities in excess of 20 m/s. Applications as diverse as printing, microfabrication, and microarraying benefit from this technology; however, reliable manipulation of the jet, including basic on/off control and steering of droplet streams and individual liquid droplets, remains difficult to achieve. We have developed a novel deflection scheme to manipulate the trajectories of droplets rebounding at shallow angles from a solid substrate based on the dielectrophoretic force exerted by patterned electrodes. Droplet rebound, key to the performance of this scheme, has been investigated for both fluorocarbon (Teflon) and superhydrophobic surface coatings. Our experiments reveal interesting droplet behavior, and at least two regimes of operation, that are dependent on the Weber number and on the properties of the solid surface with which the droplets collide and rebound. This work was supported by a grant from Eastman Kodak Co. in Rochester, NY (USA).
Hye-Won Kang (University of Minnesota) The optimal size for space discretization in spatially nonuniform reaction-diffusion systems
Abstract: In this talk, I will discuss how to discretize space to model stochastic reaction-diffusion systems. A system with chemical reactions and diffusion is modeled using a continuous time Markov jump process. Diffusion is described as a jump to the neighboring compartments with proper spatial discretization. Considering stationary mean and variance of each species in each compartment, the optimal size for spatial discretization will be suggested. Then, I will show criteria to discretize the corresponding deterministic reaction-diffusion equation for concentration of species. The optimal size for spatial discretization obtained from the deterministic case coincides with the result of the stochastic case. This is a joint work with Hans Othmer and Likun Zheng.
Yutaka Kazoe (Georgia Institute of Technology) Interfacial dynamics of colloidal particles in electrokinetically driven flows measured by multilayer nano-particle image velocimetry (MnPIV)
Abstract: The transport and dynamics of colloidal particles near a solid-liquid interface (i.e., the wall) is important in many microfluidic applications, including microscale particle-image velocimetry (PIV). Experimental studies using total internal reflection microscopy to study near-wall colloidal particle dynamics have for the most part only considered a single particle in a quiescent fluid. In contrast, our group has developed an evanescent wave-based technique that analyzes the dynamics of ensembles of up to O(105) near-wall colloidal tracers, multilayer nano-particle image velocimetry (MnPIV). The technique exploits the exponentially decaying intensity of evanescent-wave illumination, to extracts near-wall particle distributions and flow velocities at different distances from the wall, all within about 500 nm of the wall. The technique has already been validated for steady and creeping Poiseuille flow, where the shear rates were found to be within about 5% of analytical predictions. In this study, we use MnPIV to investigate electrokinetically driven flows through fused-silica microchannels about 40 microns deep. The results for 100 nm to 500 nm diameter tracers show that the flows are uniform with constant electroosmotic mobility, and that the Brownian diffusion coefficients for tangential fluctuations are within 7% of the Faxén relation. The particle distributions near the wall are, however, in all cases, highly nonuniform, with very few particles within 100 nm of the wall due to electrostatic and van der Waals effects. Finally, the near-wall distribution of the 500 nm tracers are shown to vary with applied electric field, due presumably to dielectrophoresis and perhaps induced-charge electroosmosis.
Aditya Satish Khair (University of California, Santa Barbara) Influence of ion sterics and hydrodynamic slip on electrophoresis of a colloidal particle
Abstract: The classical theory of a spherical colloids' electrophoretic mobility is founded on the Poisson-Nernst-Planck (PNP) equations and assumes the standard hydrodynamic no-slip boundary condition at the fluid/solid interface. In the (common) limit of thin double-layers, the mobility has long been known to exhibit a maximum at some zeta potential, then decrease and asymptote to a constant value. Dukhin, O'Brien, White and others showed this to result from the importance of excess ionic surface conductivity within the double-layer. The fundamental assumptions that underpin this result are, however, subject to challenge: in recent years, a finite liquid/solid slip has been measured over a variety of surfaces, and the PNP equations predict physically impossible ion concentrations precisely at the high zeta potentials where the mobility maximum occurs. Here, we discuss the dramatic effect that hydrodynamic slip and finite-ion-size steric effects in double-layers have upon the electrophoretic mobility of spherical colloids, and therefore upon the interpretation of electrophoretic mobility measurements.
Ronald G. Larson (University of Michigan) Stretch dependency of the electrophoretic mobility of DNA
Abstract: We develop a theory on DNA electrophoresis that shows stretch-dependent electrophoretic mobility in agreement with an experiment observation. In our theory, a DNA molecule is modeled as a freely-jointed-chain, each of whose segments consists of a collinear series of charged spheres, which we call a "shish-kebab" segment. First, by calculating the interaction between charged spheres in an electric field, we show that the electrophoretic mobility of a shish-kebab segment is dependent on the orientation relative to the direction of the electric field. Then, the electrophoretic mobility of the whole DNA chain is evaluated by taking an ensemble average over the orientation of the shish-kebab segments in the chain. The result shows an enhancement of the magnitude of the electrophoretic mobility under the stretch of the DNA molecule.
Reinhard Lipowsky (Max Planck Institute for Colloids and Interfaces) Wetting of structured substrates and flexible membranes
Abstract: Keywords: Wetting phenomena, surface domains, surface topography, contact line pinning, fluid membranes, vesicles, intrinsic contact angles Abstract: Two types of wetting phenomena will be discussed: (i) Morphological wetting transitions at chemically patterned or topographically structured substrates; and (ii) Wetting of flexible membranes such as lipid bilayers by aqueous phases. Morphological wetting transitions between different droplet shapes occur, e.g., as one varies the amount of liquid deposited on the structured substrate. [1,2] The basic mechanism underlying this polymorphism is the freedom of contact angles at pinned contact lines. [3] The second system consists of lipid vesicles containing aqueous solutions with two species of water-soluble polymers. When the polymer concentrations are raised by deflation, the aqueous solution forms two coexisting liquid phases that may undergo complete-to-partial wetting transitions at the vesicle membranes. [4] Partial wetting is characterized by effective contact angles that can be measured by optical microscopy and by an intrinsic contact angle that represents a 'hidden' material parameter. [5] [1] R. Seemann et al. PNAS 102, 1848 (2005)
[2] P. Blecua, M. Brinkmann, R. Lipowsky, and J. Kierfeld. Langmuir (in press)
[3] R. Lipowsky et al. J. Phys.: Condens. Matter 17, S2885 (2005)
[4] Y.-H. Li, R. Lipowsky, and R. Dimova. JACS 130, 12252 (2008)
[5] H. Kusumaatmaja, Y.-H. Li, R. Dimova, and R. Lipowsky. Phys. Rev. Lett. (submitted)
Chun Liu (University of Minnesota) Energetic variational approaches in calcium and sodium channels
Abstract: Keywords: Energetic Variational Approaches, ion channels, complex fluids Abstract: Ion channels are key components in a wide variety of biological processes, such as nerve impulse, cardiac and muscle contraction, regulating the secretion of hormones into the bloodstream. Ion channels are a frequent target in the search of new drugs. Ion channels, like enzymes, have their specific properties: potassium, sodium, calcium, and chloride channels allow only that type of ions to move through the pores. This selectivity is the key to all those biological process mentioned above. Selectivities in both calcium and sodium channels can be described by the reduced models, taking into consideration of dielectric coefficient and ion particle sizes, as well as their very different primary structure and properties. The side-chains are represented only as charged spheres (calcium channel EEEA/EEEE; sodium channel DEKA). These self-organized systems will be modeled and analyzed with energetic variational approaches (EnVarA) that were motivated by classical works of Rayleigh and Onsager. The resulting/derived multiphysics-multiscale systems automatically satisfy the Second Laws of Thermodynamics and the basic physics that are involved in the system, such as the microscopic diffusion, the electrostatics and the macroscopic conservation of momentum, as well as the physical boundary conditions. In this talk, I will discuss the some of the related biological, physics, chemistry and mathematical issues. This is a joint work with Bob Eisenberg (Rush) and Yunkyong Hyon (IMA).
Detlef Lohse (Universiteit Twente) Hydrodynamics challenges in inkjet printing
Abstract: Keywords: inkjet printing, bubbles, drop formation, air entrainment, impact Abstract: Piezo-acoustic inkjet printing has become a mature technique for high performance printing. Nevertheless, there are still various scientific challenges. In this overview talk I will cover some of them:
(i) Coupling between the fluid dynamics and the acoustics, in particular when a disturbing bubble has been entrained in the ink channel.
(ii) Optical and acoustical monitoring of the bubble.
(iii) Mechanisms of the bubble entrainment.
(iv) Droplet formation and pinch-off of droplets.
(v) Droplet impact on substrates. Main further contributors to the research: Jos de Jong, Roger Jeurissen, Arjan van der Bos, Michel Versluis, and the colleagues from Oce Technologies: Hans Reinten, Herman Wijshoff, and Marc van der Berg.
Detlef Lohse (Universiteit Twente) Wetting transition, drop impact, and microfow on hydrophobic microstructures
Abstract: Joint work with Peichun Amy Tsai1, Christophe Pirat1, Alisia M. Peters2, Rob Lammertink2, Matthias Wessling2, Sergio Pacheco3 and Leon Lefferts3. The poster presents several different wetting phenomena on structured and unstructured superhydrophobic surfaces, namely (i) an evaporation triggered wetting transition, at which a drop on a structured surface jumps from the Cassie-Baxter state to the Wenzel state, (ii) a drop impact on carbon nanofiber jungles, for which eithers droplet rebound or splashes are achieved, depending on the impact velocity, and (iii) the measurement of the effective slip-length over micro-grooves through micro-PIV. 1Physics of Fluids Group,
2Membrane Technology Group,
3Catalyst Materials and Process Group, University of Twente, the Netherlands
Shreyas Mandre (Harvard University) A fluid mechanical origin of sheet ejection during droplet impacting a dry surface
Abstract: No abstract
Vasileios Maroulas (University of Minnesota) Variational representations, small noise large deviations and applications
Abstract: Variational representations for infinite dimensional Brownian motions and Poisson random measures are considered in order to establish small noise (uniform) large deviations. Using this approach, a large deviation principle for a class of stochastic reaction-diffusion equations is established under conditions that are substantially weaker than those available in the literature, and large deviation estimates for a family of infinite dimensional stochastic flows of diffeomorphisms that arise in certain image analysis problems are demonstrated. The small noise large deviations results for the stochastic diffeomorphic flows are then applied to a stochastic Bayesian formulation of an image matching problem, and an approximate maximum likelihood property is shown for the solution of an optimization problem involving the large deviations rate function. This talk is based on joint works with A. Budhiraja and P. Dupuis.
Michael J. Miksis (Northwestern University) Dynamics of lipid bilayer membranes
Abstract: The dynamics of a lipid bilayer membrane is investigated in several different situations. Our model accounts for the transport of lipids along each monolayer, and intermonolayer friction, as well as the membrane fluidity and resistance to bending. First we consider a nearly-spherical vesicle in a shear flow. In this near-spherical limit we can reduce the model to a nonlinear coupled system of equations for the dynamics of the shape and the bilayer density difference. Multiple solution states are found as a function of viscosity ratio and the monolayer slip coefficient. Second, we investigate the stability of a planar membrane subjected to a DC electric pulse. The thin lipid membrane is impermeable to ions and thus acts as a capacitor. A linear stability analysis results in a time dependent system of equations for the growth rate as a function of wave number. Our theoretical findings are relevant to understanding the physical mechanisms of electroporation of biomembranes. Finally we discuss a novel computational method to determine the dynamics of a lipid bilayer vesicle in a viscous flow.
Chaouqi Misbah (Université de Grenoble I (Joseph Fourier)) Vesicles and red blood cells under shear and Poiseuille flow
Abstract: Keywords: Blood flow, microcirculation, modeling, rheology Abstract: Various rich dynamics of vesicles under linear and nonlinear flows will be discussed. We present analytical and numerical results on tank-treading motion, tumbling and vacillating-breathing (aka swinging, trembling). We then discuss the notion of transverse migration due to a wall and to a nonlinear flow. We show theoretical and exeprimental results on the law of transverse migration in a microfluidic device. Finally, we present very recent results on a longstadning puzzle of the blood microcirculatory research: why do red blood cells adopt a non symmetric shape (called slipper) in small blood vessels? A key result of our study is that the parachute symmetric shape is shown to be unstable, while the slipper shape is stable. That is, small flow disturbances–which are always present in real blood flows–cause RBCs to assume slipper shapes. It is further shown that the slipper shape offers a better transport efficiency to RBCs. In addition the slipper shape favors hemoglobin mixing in the cell, and thus enhances oxygen transport efficiency. Blood flow efficiency together with optimal oxygen supply seem to be determinant for natural selection of slipper shapes.
Frieder Mugele (Universiteit Twente) Mixing and internal flows in drops in AC electrowetting
Abstract: Keywords: Electrowetting, mixing, electrothermal flow Abstract: Mixing is a key issue in microfluidics, including droplet-based “digital” microfluidics. In electrowetting, internal flow patterns inside drops can be generated without any lateral translation if the drops are excited with AC voltage. Two regimes can be distinguished: at AC frequencies of the order of the eigenfrequency (typically O(1kHz) or less), the drops periodically oscillate between states of high and low contact angle. Despite the periodicity, there is a symmetry breaking in the drop shape between the spreading and the receding phase, which causes a time-averaged net flow inside the drop that promotes mixing. This process can be described using a model based on capillary wave-driven Stokes drift. For somewhat higher frequencies, this mechanism becomes progressively inefficient, because the liquid cannot follow the applied voltage anymore. At substantially higher AC frequencies (typically >>10kHz, depending on the salt concentration), however, a new driving mechanism for internal flows sets in, as reported by Nichols and Gardniers (Anal. Chem. 79, 8699 (2007) and by Ko et al. (Langmuir 24, 1094, 2008). Under these conditions, the liquid no longer acts as a perfect conductor. The electric field penetrates into the drop and generates local Ohmic currents. These currents produce Joule heating and ultimately giving rise to electro-thermal flows inside the drops. Solving numerically for the distribution of the electrostatic field, the flow field, and the temperature distribution, we show that the flow velocity scales with the fourth power over a wide range of both the applied voltage and the AC frequency – in good agreement with the experiments by Ko et al.
Frieder Mugele (Universiteit Twente) Surface charge measurement and control by gate voltage in electroosmotic flow
Abstract: We present a simple analytical model that allows for determining the surface charge in electro-osmotic flow channels using the so-called solution displacement method. In contrast to earlier techniques, which have either been limited to small ratios of salt concentration or required a numerical solution of the convection-diffusion equation, our method provide a simple functional form with merely two fit parameters and thus allow for more accurate measurements of surface charge. Moreover, we demonstrate flow reversal inside our microfluidic channels controlled by gate electrodes underneath insulating layers that allow for external tuning of the surface charges. We discuss possible applications as a rheometer for applying shear forces to ultrasoft complex fluids.
Susan J. Muller (University of California, Berkeley) Confinement effects with macromolecules
Abstract: No Abstract
Ali Nadim (Claremont Graduate University) Electrowetting and digital microfluidics
Abstract: In this tutorial, a number of approaches to mathematical modeling of electrowetting-on-dielectric (EWOD), also known as digital microfluidics (DMF) will be reviewed. EWOD refers to methods for causing droplets to move along solid surfaces or changing the shapes of attached drops (e.g., to actuate a liquid lens) by applying a potential difference between the drop and an underlying electrode, separated from the conducting drop via a thin dielectric layer. The main equation describing electrowetting is known as the Young-Lippmann (YL) equation, which provides a relationship between the local contact angle of the drop and the square of the potential difference. In this tutorial, a simple derivation of the YL equation is provided based on an energy minimization principle. We will then introduce both lumped and field models to characterize the electrostatic forces acting on a drop as a function of its position relative to the underlying electrodes. The lumped model is based simply on treating the dielectric layer as a parallel-plate capacitor and considering the changes in the energy of the system as a function of the location of the drop. The field model requires the use of concepts from electromechanics, including Maxwell's electric stress tensor. We will consider both DC and AC electric potentials and describe how to analyze the system in both cases.
Monika Nitsche (University of New Mexico) High order quadratures for the evaluation of interfacial velocities in axi-symmetric Stokes flows
Abstract: Boundary integral methods are computationally efficient in computing the evolution of interfaces in Stokes flow. For axisymmetric interfaces, they reduce to evaluating a 1d integral at each time step. We have performed a detailed analysis of the structure of the integrands and show that standard methods of integration present two difficulties. One arises from loss of precision due to cancellation, the other from singular behaviour of the integrands near the axis of symmetry. As a result, high order quadrature proposed previously for these types of integrals are not uniformly high order. Instead, the maximal errors are always of second order. We propose a remedy to both difficulties and present a uniformly accurate 5th order approximation. This new quadrature is implemented to evolve (1) an initially bar-belled bubble that pinches at a point in finite time, and (2) a sphere in a strain flow that approaches a steady state. We compare the results with commonly used second order approximations and show that significant improvement is obtained using 5th order rules. The examples also illustrate when the corrections needed for uniformity have an impact in practice.
Peter D. Olmsted (University of Leeds) The influence of boundaries on shear banding in complex fluids
Abstract: Keywords: shear banding, boundary conditions, flow instabilities, wormlike micelles Abstract: Shear banding fluids such as wormlike micelles, lamellar surfactant solutions, and emulsions, undergo "transitions" between fluids of different apparent viscosity as a function of applied flow conditions. This switching makes them appealing for use in microfluidic applications. Since their physics is controlled by the influence of flow on internal microstructure, which in turn is influenced by boundary effects, it is important to develop an understanding of how different kinds of boundary effects influence shear banding. In this talk I will discuss some of these issues, mainly using constitutive models inspired by experiments on wormlike micelles or polymer solutions. and explore the effects of different boundary conditions for the additional viscoelastic stress. These are needed because the equations of motion are inherently non-local and include “diffusive” or square-gradient terms. I will note some of the features expected to be important for microfluidic geometries. [Work done in collaboration with JM Adams and SM Fielding]
Sumita Pennathur (University of California, Santa Barbara) Electrokinetics in planar nanofluidic channels
Abstract: Keywords: electrokinetics, nanofluidics, possion-boltzmann, TIRFM Abstract: The advent of nanofabrication technologies allows for the development of robust nanoconfined fluidic channels. In this talk I will outline some recent advances and challenges in our research program aimed at elucidating linear and nonlinear electrokinetic phenomena within such channels. First, I will present a combined theoretical and experimental study of the dissolution of fused silica nanofluidic channels when subject to pressure driven flow of aqueous solutions. Time sensitive current measurements within these channels allow for determination of the dissolution rate from the classic linear Poisson-Boltzmann equations for fluid flow and Gouy-Chapman-Stern-Grahame charge regulation model for the surface boundary conditions. Next, I will describe a novel total internal reflectance microscopy (TIRFM) system we have developed and recent experimental results towards to the elucidation of coupled nanofluidic electrokinetic systems, namely, the addition of finite sized charged quantum dots and/or biomolecules on the order of the size of the channel. Finally, I will discuss some experimental nonlinear electric-field dependent phenomena observed around metal electrodes within a nanofluidic channel.
Jonathan D. Posner (Arizona State University) Locomotion of synthetic nanomotors
Abstract: At ASU, we are investigating locomotion of bimetallic synthetic nanomotors that, analogous to their biological counterparts, harvest chemical energy from their local environment and convert it to useful work. Bimetallic nanorods can autonomously propel themselves at a hundred body lengths per second through aqueous solutions by using hydrogen peroxide as a fuel. Magnetic fields and electrochemically induced chemical species are used to control the motion of Pt-Ni-Au nanorods. We use the magnetic properties of nickel-loaded nanomotors to control their motion through micron-scale structures as well as the loading, transport, and release of spherical cargo that have volumes two orders of magnitude larger than the nanomotors itself. Nanomotor locomotion forces are determined by measuring their velocity while towing spherical cargo that have Stokes drag eight times the nanomotors themselves. Several physical arguments have been proposed to describe the physics underlying chemically-powered locomotion, but there is no detailed theory on the propulsion mechanism. We are simulating the physics of rod-shaped nanoparticles with asymmetric surface fluxes. Our models show that locomotion is driven by electric body forces in the fluid that arise due to finite space charge and internally generated electric fields surrounding the rod. The electric fields and charge density are generated by dipolar cation fluxes, such as those generated by heterogeneous electrochemical reactions with broken symmetry. The scaling analysis and detailed simulations predict that the nanomotor velocity depends on the reaction flux, nanorod electrical surface potential, solvent viscosity, and rod geometry.
Manu Prakash (Harvard University) Programmable soft matter
Abstract: Our interests lie in exploiting physical fluidic mechanisms to program and control matter at small length scales. In the first part of the talk, I will describe a novel way to employ physical computation to build all-fluidic control circuits. I will introduce how to build both "analog" and "digital" circuits that can implement universal Boolean logic, feedback, cascadability, bistability and synchronization via exploiting purely hydrodynamic nonlinearities in low-Reynolds number multi-phase flow. These circuits provide a means to control sub-nanoliter droplets in fluidic channels up to KHz regime with no moving parts. In the second part of the talk, I will describe techniques for in-situ synthesis of morphologically diverse nanostructures via geometrical control. By physically coupling growth and transport dynamics of reactants in a continuous flow reactor, we demonstrate programmed synthesis of complex geometrical patterns of Zinc Oxide nanowires in microchannels. Time permitting, I will discuss some of our on-going work on development of new tools for stretching biomolecules.
David Quéré (École Supérieure de Physique et de Chimie Industrielles de la Ville de Paris (ESPCI)) Impact figures
Abstract: Since Worthington, many situations generated by impacts in liquids were documented and explored. In this spirit, we would like to present several recent observations related to the behavior of projectiles after they hit different kinds of liquids. We first discuss the impact on soap films, and naturally extend these observations to foams, focussing on the ability of such complex fluids to absorb the kinetic energy of the projectiles. We also consider impacts in a viscous liquid, and describe the particular kind of cavity generated by the shock. And we conclude by looking at the behaviour of revolving projectiles, discussing the characteristics of the trajectory induced by the rotation. Other contributors to this talk: Anne Le Goff, Guillaume Dupeux and Christophe Clanet.
Antonio Ramos (University of Sevilla) Traveling-wave electroosmosis and faradaic currents: the diffusion layer
Abstract: Pumping of electrolytes in microchannels can be achieved with arrays of microelectrodes subjected to AC potentials. Here we show experiments on electrolyte flow induced by microelectrodes subjected to traveling-wave potentials. For sufficiently high voltages, Faradaic currents are present, leading to changes in the liquid properties and, in particular, changes in pH. A remarkable feature of the observations is that at voltages above a threshold, the direction of the fluid flow is reversed. These observations motivate the theoretical study of Faradaic currents in electrokinetics for the general case of ionic species with different mobilities. We find, using a linear analysis, that the structure of the electrical double layer (EDL) has to be extended. The EDL consists of the compact and Debye layers, as in previous models, plus a diffusion layer that arises as a consequence of Faradaic currents. For the general case of different mobilities, there is a net electrical charge associated to the diffusion layer. As a particular result of this model, we show that traveling potentials generate flow in the reverse direction for the case of a thick compact layer and facile Faradaic reactions, if the reacting ions are the more mobile. This situation is consistent with the experimental observation of changes in pH due to proton reactions at the electrodes.
Isaak Rubinstein (Ben Gurion University of the Negev) Extended space charge effects in concentration polarization
Abstract: Keywords: Extended Space Charge, Concentration Polarization, Overlimiting Conductance, Nonequilibrium Electroosmotic Instability Abstract: Our talk is about ionic currents from an electrolyte solution into a charge selective solid, such as, an electrode, an ion exchange membrane or an array of nano-channels in a micro-fluidic system, and the related viscous fluid flows on the length scales varying from nanometers to millimeters. All systems of this kind have characteristic voltage-current curves with segments in which current nearly saturates at some plateau values due to concentration polarization – formation of solute concentration gradients under the passage of a DC current. We start by reviewing a few seemingly different phenomena occurring in that range. These are anomalous rectification in cathodic copper deposition from a copper sulfate solution, super-fast vortexes near an ion-exchange granule, over-limiting conductance in electrodialysis and the recently observed non equilibrium electroosmotic instability. All these phenomena result from formation of an additional extended space charge layer next to that of a classical electric double layer at the solid/liquid interface. We review the peculiar features the extended space charge and their relation to the mechanisms of the above mentioned phenomena.
Riccardo Sacco (Politecnico di Milano) Multi-physics computational models for neuro-chip simulation
Abstract: Neuro-chips (NCs) are bio-hybrid devices in which living brain cells and silicon circuits are coupled together. NCs are presently being used as a non-invasive technique to record cellular response to drugs, and are expected to be used in the cure of neurological disorders through the creation of sophisticated neural prostheses. The main technological challenge in the design of NCs is the efficient transduction of the input biological signal (ion current of the order of nA) into an output signal (electrical current) which is modulated by the effective driving voltage of the open Gate of the silicon device (of the order of mV). In order to devise a sound simulation tool of the I/O behavior of a NC device, we propose a multi-physics computational model including:
1) the Poisson-Nernst-Planck system, to account for intracellular and extracellular electrochemical ion transport;
2) the Hodgkin-Huxley system, to describe ion transport across membrane channels;
3) a nonlinear MOS capacitor approximation, to account for cell-to-chip coupling.
The nonlinear system arising from the coupled solution of 1)-3) is successively solved by a functional iteration procedure, and for each time level of the simulation, each obtained sub-problem is numerically solved using a stabilized mixed-hybridized finite element discretization scheme. In order to provide a successful validation of the computational procedure, we discuss preliminary results on two cases of physiological interest, namely, the Hodgkin-Huxley axon and the response of a field-effect transistor with metal-free gate oxide under an intracellular voltage depolarization stimulating impulse.
David Saintillan (University of Illinois at Urbana-Champaign) Electrokinetic phenomena in particulate suspensions: an introduction
Abstract: No Abstract
Charles M. Schroeder (University of Illinois at Urbana-Champaign) Hydrodynamic trap for single cells, particles and molecules
Abstract: The ability to trap individual particles, cells and macromolecules has revolutionized many fields of science during the last two decades. Several methods of particle trapping and micromanipulation have been developed based on optical, magnetic and electric fields. In this work, we describe an alternative trapping method, the hydrodynamic trap, based on the sole action of hydrodynamic forces in a microfluidic device. A microfluidic cross slot device is fabricated consisting of two perpendicular microchannels where opposing laminar flow streams converge. In this device, a purely extensional flow field is created at the microchannel junction, thereby resulting in a semi-stable potential well at the stagnation point which enables particle trapping. We implement an automated feedback-control mechanism to adjust the location of the stagnation point which facilitates active particle trapping. Using the hydrodynamic trap, we successfully demonstrate trapping and manipulation of single particles and cells for arbitrarily long observation times. This technique offers a new venue for observation of biological materials without surface immobilization, eliminates potentially perturbative optical, magnetic and electric fields, and provides the capability to change the surrounding medium conditions of the trapped object during observation.
Eric S. G. Shaqfeh (Stanford University) The microfluidics of colloidal particle-vesicle-capsule mixtures with application to blood additives
Abstract: Keywords: Brownian rods, surfboards, drug delivery, capsules, vesicles, margination Abstract: Many dispersions of colloidal particles with application in materials processing, biological assays, or medicine, contain elongated particles (e.g. ellipsoidal disks, rods, etc.) Recently these particles have been used in drug delivery applications because of the inability of leukocytes to easily rid them from the circulation. Moreover such particles are useful at the nanoscale for application in cancer therapies, either for detection of tumor vasculature or for the delivery of anti-cancer agents to tumor endothelial cells. Thus, the study of anisotropic particulate flows with adhesion in microchannels especially in mixtures with vesicle flows (i.e. red blood cells) has taken on a particularly important set of engineering applications. In order to understand the transport in these systems, a numerical simulation must include: a) a high fidelity representation of nonequilibrium dynamics of vesicles and capsules in microflows, b) the dynamic simulation of Brownian colloidal particles of general shape in microflows, and c) the combination of these in mixtures at finite concentration. Each of these transport processes brings in new physics which we will review. In discussing a) we will focus on the transition between tank-treading, tumbling, and trembling dynamics in flow and whether these transitions also happen at finite concentration in microfluidics. In b) we will discuss the particle concentration distribution of Brownian nonspherical particles in microfluidic flows and its relation to the nonequilibrium osmotic pressure. In c) we will examine how particle margination in mixtures occurs and how it is related to the concentration of vesicles/capsules in the microflow. Ultimately, we will look toward the virtual prototyping and engineering of these therapies.
John D. Sherwood (University of Cambridge) Electrical streaming potential generated by 2-phase flow
Abstract: Keywords: Streaming potential, multiphase flow, porous media Abstract: Streaming potentials generated by single phase flow are reasonably well-understood, but much less is known about the effects of multiphase flow. The introduction of a second fuid phase can either increase the wall shear rate (thereby increasing streaming currents caused by convection of ionic charge clouds), or can decrease it, depending on the ratio of the viscosities of the two phases and on the effect of interfacial tension. If the second phase is non-conducting (e.g. oil droplets in water), the effective conductivity of the mixture is decreased, and streaming potentials tend to increase. I shall review the few experimental results that are available, and describe recent theoretical work aimed at understanding the effect of a single particle or fluid droplet flowing through a capillary. J.D. Sherwood, Streaming potential generated by two-phase flow in a capillary. Phys. Fluids, 19 (2007) 053101. J.D. Sherwood, Streaming potential generated by a long viscous drop in a capillary. Langmuir, 24 (2008) 10011. E. Lac & J.D. Sherwood, Streaming potential generated by a drop moving along the centreline of a capillary. J. Fluid Mech. (in the press)
Zuzanna S. Siwy (University of California, Irvine) Ion transport through nanopores: From living cells to diodes and transistors
Abstract: Keywords: nanofluidics, channel, diode, ion current Abstract: Transport through nanopores and ion channels exists in virtually all biological cells and is important in such things as the regulation of heart function, nerve signals, and delivery of nutrients to the cell. Nanopores have also started to play a major role in contemporary biotechnology, because many separation and sensing processes require pores with nanometer-sized openings. My scientific interests have been focused on fabricating synthetic single nanopores with applications in biophysics and nanotechnology. The nanopores that we fabricate by the track-etching technique have diameters as small as 1 nanometer, they have controlled geometry and surface chemistry. I will show application of these nanopores as devices for controlling the flow of ions and charged molecules in a solution, functioning as ionic bipolar and unipolar diodes as well as ionic transistors. These functions are achieved by patterning the surface charge of the pore walls. Our systems will be applicable in nanofluidic, lab-on-the-chip, and biosensing systems. An example for application of ionic diodes in building sensors for anthrax will be discussed. I will also show how to induce ion current oscillations in time with frequencies between tens of Hz and fractions of Hz.
Todd Squires (University of California, Santa Barbara) Electrokinetics of highly charged surfaces
Abstract: No Abstract
Paul H. Steen (Cornell University) Countering capillarity with electrokinetics: from micro-manipulation to Debye-layer diagnostics
Abstract: Electroosmosis, originating in the Debye-layer near the solid/liquid boundary within a fully-saturated porous substrate, can pump successfully against the capillary pressure arising from the surface tension of a droplet placed in series with the pump. As droplet size diminishes, the voltage required to pump electroosmotically down-scales favorably. The technological implication is that electromechanical transducers made of large arrays of small droplets, so-called 'droplet micro-manipulators', and Debye-layer 'diagnostic machines', inferring zeta-potential by measuring interface deflection of a droplet-pump-droplet configuration, become feasible. These applications will be illustrated and we will describe the current modeling of such multi-scale interfacial systems, highlighting open questions that might benefit from an applied mathematical approach.
Derek Stein (Brown University) Free energy landscaping: Nanotopographic control over DNA conformations and transport
Abstract: Nanofluidic devices with an embedded nanotopography direct the self-organization and transport of long DNA molecules by influencing the free energy landscape. We studied the pressure-driven transport of DNA in slit-like nanochannels containing linear arrays of nanopits. We imaged individual DNA molecules moving single-file down the nanopit array, undergoing sequential pit-to-pit hops using fluorescence video microscopy. Distinct transport dynamics were observed depending on whether a molecule could occupy a single pit, or was forced to subtend multiple pits. We interpret these results in terms of a scaling theory of the free energy of polymer chains in a linear array of pits. Molecules contained within a single pit are predicted to face an entropic free energy barrier, and to hop between pits stochastically by thermally activated transport. Molecules that subtend multiple pits, on the other hand, can transfer DNA contour from upstream to downstream pits in response to an applied fluid flow, which lowers the energy barrier. When the trailing pit completely empties, or when the leading pit reaches its capacity, the energy barrier is predicted to vanish, and the low-pressure, thermally activated transport regime gives way to a high-pressure, deterministic transport regime. These results contribute to our understanding of polymers in nanoconfined environments, and can guide the design of nanoscale lab-on-a-chip applications for DNA analysis.
Huan Sun (Pennsylvania State University) A diffusive interface method of modeling mutli-phase flows
Abstract: We present an diffusive interface approach to modeling multi-phase flows. A modified interfacial energy functional is employed to describe diffusive interfaces of (im)miscible phases. A fluid system where the Stokes equations are coupled with convection-diffusion equations are derived from the energy functional via the Energetic Variational Approaches (EVA). A particular case with slip boundary conditions on the interfaces were studied. In the numerical simulations we applied the Pressure Schur Complement (PSC) method to the hydrodynamical system. A Krylov subspace method with an Algebraic Mutligrid (AMG) preconditioner was used to solve the resulted linear system.
Vladimir Sverak (University of Minnesota) Topics in the theory of the Navier-Stokes equations
Abstract: The course will cover certain selected topics in the theory of the Navier-Stokes equations. After a brief overview of the main issues of the general theory we will focus on problems in the theory of the steady-state solutions. There are many open problems concerning the steady-state solutions. These problems are presumably easier than the main open questions about the time-dependent equations. Nevertheless, some of them have remained unsolved since their first explicit formulation in the pioneering works of Jean Leray in the 1930s. There is a certain indirect similarity (or "duality") between the mathematical issues raised by these steady-state problems and the issues which come up in connection with the more well-known open problems about the time-dependent equations. In the lectures I hope to cover some of the important results about the steady-state solutions and discuss some of the open problems. The course will be accessible to postdocs and to graduate students with some knowledge of PDEs. For example, an introductory graduate PDE course should be a sufficient prerequisite.
Ulrich Tallarek (Philipps-Universität Marburg) Electric field gradient focusing in microchannels with embedded bipolar electrode
Abstract: The complex interplay of electrophoretic, electroosmotic, bulk convective, and diffusive mass/charge transport in a hybrid poly(dimethylsiloxane) (PDMS)/glass microchannel with embedded floating electrode is analyzed. The thin floating electrode attached locally to the wall of the straight microchannel results in a redistribution of local field strength after the application of an external electric field. Together with faradaic reactions taking place at the bipolar electrode and buffer reactions, as well as bulk convection based on cathodic electroosmotic flow, an extended field gradient is formed in the anodic microchannel segment. It imparts a spatially dependent electrophoretic force on charged analytes and, in combination with the bulk convection, results in an electric field gradient focusing at analyte-specific positions. Analyte concentration in the enriched zone approaches a maximum value which is independent of its concentration in the supplying reservoirs. A simple approach is shown to unify the temporal behavior of the concentration factors under general conditions.
Lalitha Venkataramanan (Schlumberger-Doll) Research in applied mathematics at Schlumberger
Abstract: The search for oil and gas has three objectives: to identify and evaluate hydrocarbon-bearing reservoirs; to bring hydrocarbons to the surface safely and cost-effectively, without harming the environment; and to maximize the yield from each discovery. This talk will focus on some aspects of research in applied mathematics in the area of nuclear magnetic resonance and its application to the oilfield at Schlumberger.
Petia M. Vlahovska (Dartmouth College) Dynamics of drops and vesicles in electric fields
Abstract: Drop deformation in uniform electric fields is a classic problem. The pioneering work of G.I.Taylor demonstrated that for weakly conducting media, the drop fluid undergoes a toroidal flow and the drop adopts a prolate or oblate spheroidal shape, the flow and shape being axisymmetrically aligned with the applied field. However, recent studies have revealed a nonaxisymmetric rotational mode for drops of lower conductivity than the surrounding medium, similar to the rotation of solid dielectric spheres observed by Quincke in the 19th century. I will present an experimental and theoretical study of this phenomenon in DC fields. The critical electric field, drop inclination angle, and rate of rotation are measured. For small, high viscosity drops, the threshold field strength is well approximated by the Quincke rotation criterion. Reducing the viscosity ratio shifts the onset for rotation to stronger fields. The drop inclination angle increases with field strength. The rotation rate is approximately given by the inverse Maxwell-Wagner polarization time. We also observe a hysteresis in the tilt angle for low-viscosity drops. I will also discuss our work on drops encapsulated by complex interfaces such as lipid bilayer membranes. A comparison between the behavior of drops and giant vesicles (cell-size lipid membrane sacs) highlights new features due to the membrane electromechanics. This work is in collaboration with Paul Salipante (Dartmouth) and Dr. Rumiana Dimova’s group (Max Planck Institute of Colloids and Interfaces).
Ehud Yariv (Technion-Israel Institute of Technology) Migration of ion-exchange particles under the action of a uniformly applied electric field
Abstract: An ideally polarizable cation-selective solid particle is suspended in an electrolyte solution and is exposed to a uniformly applied ambient electric field. The electrokinetic transport processes are described in a closed mathematical model, consisting of differential equations, representing the physical balance laws, as well as boundary conditions and integral constraints, representing the physicochemical condition on the particle boundary and at large distances away from it. Solving this model would in principle provide the electro-kinetic flow about the particle and the concomitant particle drift relative to the otherwise quiescent fluid. Using matched asymptotic expansions, the model is analyzed in the thin-Debye-layer limit. An effective `macroscale' description is extracted, whereby effective boundary conditions represent appropriate asymptotic matching with the Debye-scale fields. The macroscale description significantly differs from that corresponding to a chemically inert ideally polarizable particle. Thus, ion selectivity on the particle surface results in a macroscale salt concentration polarization, whereby the electric potential is rendered non-harmonic. Moreover, the uniform Dirichlet condition governing this potential on the particle surface is transformed into a non-uniform Dirichlet condition on the macroscale particle boundary. The Dukhin--Derjaguin slip formula still holds, but with a non-uniform zeta potential that depends upon the salt concentration distribution. For weakly applied fields, an approximate solution is obtained as a perturbation to an equilibrium state. The linearized solution corresponds to a uniform zeta potential; it predicts a particle velocity which is proportional to the applied field. The associated electrokinetic flow differs however from that in the comparable electrophoresis of an inert particle surface, since it is driven by two different agents, electric field and salinity gradients, which are of comparable magnitude. The velocity field, specifically, is rotational.
Minami Yoda (Georgia Institute of Technology) Nonuniform interfacial colloidal tracer distributions and implications for microscale PIV
Abstract: Keywords: Interfacial particle-image velocimetry, colloidal particles, microfluidics, electrokinetically driven flows Abstract: Interfacial effects are important in many cases for microscale transport. One of the few experimental techniques that can resolve interfacial transport with sub-micron spatial resolution is evanescent wave-based, or nano-, particle-image velocimetry (PIV), which determines fluid velocities over the first 500 nm next to the wall from the displacements of 100-500 nm neutrally buoyant tracers. The wall-normal spatial resolution of nano-PIV is further improved by multilayer nano-PIV (MnPIV), which exploits the exponentially decaying intensity of evanescent-wave illumination to obtain velocities at different distances from the fluid-solid interface within about 500 nm of the wall. In agreement with DLVO theory, the distribution of the colloidal tracers within a particle diameter of the wall measured by MnPIV is highly nonnuniform due to repulsive electric double layer interactions and van der Waals effects. Nevertheless, the MnPIV results for steady creeping Poiseuille flow are in good agreement with analytical predictions once the velocities have been corrected for this nonuniform distribution. This talk describes velocity and Brownian diffusion coefficient measurements obtained from tracers with diameters ranging from 100 nm to 500 nm for Poiseuille flow through hydrophilic and hydrophobically coated fused-silica microchannels and for electrokinetically driven flows through fused-silica microchannels with a minimum cross-sectional dimension of about 40 microns. The near-wall particle distributions for 500 nm tracers are shown to vary with electric field for the electrokinetically driven flows, due presumably to electrophoresis and induced charge electroosmosis.
Gilad Yossifon (Technion-Israel Institute of Technology) Understanding electrokinetics at the nanoscale: Beyond the limiting current
Abstract: We examined the important over-limiting ionic current phenomenon, occurring at ion-permselective nanoporous membrane or nanochannel, and suggested a modified theoretical description of the entire nonlinear current-voltage curve based on the instability selected concentration-polarization layer thickness. In the process we discovered several curious and non-intuitive behaviors: 1) a nanoslot array with a uniform surface charge and height but with asymmetric slot entrances is shown to exhibit strong rectification, gating type current-voltage characteristics and a total current higher than the sum of isolated slots at a large voltage; 2) the vanishing of the limiting resistance voltage window with increased geometrical field focusing effect obtained by varying the nanoslot width. Hence, suggesting that an optimal pore radius/separation ratio exists for maximum current density across a membrane; 3) strong nanocolloid-nanoslot interaction that leads to an additional transition region (or critical voltage) prior to the overlimiting region.
Boris Zaltzman (Jacob Blaustein Institute for Desert Research) Electric double layer and concentration polarization
Abstract: No Abstract
Visitors in Residence
Shahriar Afkhami New Jersey Institute of Technology 12/7/2009 - 12/11/2009
Shelley L. Anna Carnegie Mellon University 12/5/2009 - 12/11/2009
Noritoshi Araki University of Minnesota 12/7/2009 - 12/11/2009
Noritoshi Araki University of Minnesota 12/5/2009 - 12/6/2009
Paul J. Atzberger University of California, Santa Barbara 12/8/2009 - 12/11/2009
Nusret Balci University of Minnesota 9/1/2009 - 8/31/2010
Jaydeep P. Bardhan Argonne National Laboratory 12/5/2009 - 12/11/2009
Jaydeep P. Bardhan Argonne National Laboratory 12/1/2009 - 12/4/2009
Martin Z. Bazant Massachusetts Institute of Technology 12/6/2009 - 12/8/2009
Jennifer Beichman University of Michigan 9/1/2009 - 5/31/2010
Olus N. Boratav Corning Incorporated 12/5/2009 - 12/11/2009
John F. Brady California Institute of Technology 12/4/2009 - 12/11/2009
Richard J. Braun University of Delaware 9/1/2009 - 12/15/2009
Michael P. Brenner Harvard University 12/9/2009 - 12/10/2009
Henrik Bruus Technical University of Denmark 12/5/2009 - 12/11/2009
Thomas P. Burg Max-Planck-Institut für Biophysikalische Chemie 12/6/2009 - 12/11/2009
Wei Cai University of North Carolina - Charlotte 12/7/2009 - 12/10/2009
Maria-Carme T. Calderer University of Minnesota 9/1/2009 - 6/30/2010
Chi Hin Chan University of Minnesota 9/1/2009 - 8/31/2010
Hsueh-Chia Chang University of Notre Dame 12/6/2009 - 12/11/2009
Xianjin Chen University of Minnesota 9/1/2008 - 8/31/2010
Zhen Chen Northwestern University 12/4/2009 - 12/12/2009
Greg P. Chini University of New Hampshire 12/4/2009 - 12/11/2009
Tom Chou University of California, Los Angeles 12/6/2009 - 12/11/2009
A. Terrence Conlisk Ohio State University 12/6/2009 - 12/11/2009
L. Pamela Cook University of Delaware 9/6/2009 - 12/12/2009
Michael Earl Cromer Jr University of Delaware 9/1/2009 - 12/20/2009
Darren G. Crowdy Imperial College London 12/4/2009 - 12/9/2009
Linda J. Cummings New Jersey Institute of Technology 12/8/2009 - 12/11/2009
M. Cristina Depassier Pontificia Universidad Catolica de Chile 12/4/2009 - 12/13/2009
Shu Ding University of Minnesota 12/7/2009 - 12/11/2009
Charles Doering University of Michigan 8/15/2009 - 6/15/2010
Kevin D. Dorfman University of Minnesota 12/6/2009 - 12/11/2009
Patrick S. Doyle Massachusetts Institute of Technology 12/6/2009 - 12/9/2009
Jens Eggers University of Bristol 12/5/2009 - 12/12/2009
Robert S. Eisenberg Rush University Medical Center 12/4/2009 - 12/10/2009
Randy H. Ewoldt University of Minnesota 9/1/2009 - 8/31/2010
Marco Antonio Fontelos Consejo Superior de Investigaciones Científicas (CSIC) 12/2/2009 - 12/12/2009
Sandip Ghosal Northwestern University 9/21/2009 - 12/12/2009
Michael D. Graham University of Wisconsin 9/1/2009 - 12/17/2009
J. Michael Gray Medtronic 12/4/2009 - 12/4/2009
Günther Grün Friedrich-Alexander-Universität Erlangen-Nürnberg 12/5/2009 - 12/12/2009
Thomas C. Hagen University of Memphis 9/1/2009 - 12/23/2009
Yunkyong Hyon University of Minnesota 9/1/2008 - 8/31/2010
Mark Iwen University of Minnesota 9/1/2008 - 8/31/2010
Srividhya Jeyaraman University of Minnesota 9/1/2008 - 8/31/2010
Lijian Jiang University of Minnesota 9/10/2008 - 8/31/2010
Thomas B. Jones University of Rochester 12/6/2009 - 12/11/2009
Mihailo Jovanovic University of Minnesota 9/11/2009 - 6/10/2010
Hye-Won Kang University of Minnesota 12/15/2009 - 12/15/2009
Dmitry Karpeev Argonne National Laboratory 12/1/2009 - 12/4/2009
Yutaka Kazoe Georgia Institute of Technology 12/6/2009 - 12/11/2009
Markus Keel University of Minnesota 7/21/2008 - 6/30/2010
Aditya Satish Khair University of California, Santa Barbara 12/6/2009 - 12/11/2009
Hyejin Kim University of Minnesota 9/1/2009 - 8/31/2010
Scott King University of Minnesota 12/7/2009 - 12/11/2009
Matthew Gregg Knepley Argonne National Laboratory 12/1/2009 - 12/4/2009
Pawel Konieczny University of Minnesota 9/1/2009 - 8/31/2010
Satish Kumar University of Minnesota 12/6/2009 - 12/11/2009
Nabil Laachi University of Minnesota 12/7/2009 - 12/11/2009
Nabil Laachi University of Minnesota 12/5/2009 - 12/6/2009
Ronald G. Larson University of Michigan 9/12/2009 - 12/18/2009
Eric Lauga University of California, San Diego 12/6/2009 - 12/10/2009
Chiun-Chang Lee National Taiwan University 10/22/2009 - 6/30/2010
Young-Ju Lee Rutgers University 9/11/2009 - 12/14/2009
Marta Lewicka University of Minnesota 9/1/2009 - 6/30/2010
Yi Li Stevens Institute of Technology 9/16/2009 - 12/17/2009
Yongfeng Li University of Minnesota 9/1/2008 - 8/31/2010
Tai-Chia Lin National Taiwan University 11/29/2009 - 12/10/2009
Zhi (George) Lin University of Minnesota 9/1/2009 - 8/31/2010
Maggie Linak University of Minnesota 12/7/2009 - 12/11/2009
Reinhard Lipowsky Max Planck Institute for Colloids and Interfaces 12/5/2009 - 12/10/2009
Chun Liu University of Minnesota 9/1/2008 - 8/31/2010
Detlef Lohse Universiteit Twente 12/6/2009 - 12/10/2009
Ellen K. Longmire University of Minnesota 9/1/2009 - 6/30/2010
Yasunori Maekawa Kobe University 9/7/2009 - 3/1/2010
Krishnan Mahesh University of Minnesota 9/1/2009 - 6/30/2010
Kara Lee Maki University of Minnesota 9/1/2009 - 8/31/2010
Shreyas Mandre Harvard University 12/4/2009 - 12/12/2009
Vasileios Maroulas University of Minnesota 9/1/2008 - 8/31/2010
Michael J. Miksis Northwestern University 12/6/2009 - 12/11/2009
Chaouqi Misbah Université de Grenoble I (Joseph Fourier) 12/8/2009 - 12/11/2009
Yoichiro Mori University of Minnesota 9/1/2009 - 6/30/2010
Frieder Mugele Universiteit Twente 12/6/2009 - 12/11/2009
Susan J. Muller University of California, Berkeley 12/5/2009 - 12/11/2009
Ali Nadim Claremont Graduate University 12/4/2009 - 12/11/2009
Monika Nitsche University of New Mexico 9/1/2009 - 12/18/2009
Peter D. Olmsted University of Leeds 12/6/2009 - 12/11/2009
Daniel W Olson University of Minnesota 12/7/2009 - 12/11/2009
Cecilia Ortiz-Duenas University of Minnesota 9/1/2009 - 8/31/2010
Hans G. Othmer University of Minnesota 9/1/2009 - 6/30/2010
Jia Ou University of Minnesota 12/7/2009 - 12/11/2009
Sumita Pennathur University of California, Santa Barbara 12/6/2009 - 12/11/2009
Jonathan D. Posner Arizona State University 12/6/2009 - 12/11/2009
Manu Prakash Harvard University 12/6/2009 - 12/11/2009
David Quéré École Supérieure de Physique et de Chimie Industrielles de la Ville de Paris (ESPCI) 12/5/2009 - 12/11/2009
Antonio Ramos University of Sevilla 12/6/2009 - 12/11/2009
Michael Renardy Virginia Polytechnic Institute and State University 9/1/2009 - 12/12/2009
Yuriko Renardy Virginia Polytechnic Institute and State University 9/1/2009 - 12/12/2009
Juan Mario Restrepo University of Arizona 8/11/2009 - 6/15/2010
Scott Alan Roberts University of Minnesota 12/7/2009 - 12/11/2009
Isaak Rubinstein Ben Gurion University of the Negev 12/6/2009 - 12/11/2009
Rolf Ryham Rice University 12/4/2009 - 12/11/2009
Riccardo Sacco Politecnico di Milano 12/4/2009 - 12/11/2009
David Saintillan University of Illinois at Urbana-Champaign 12/4/2009 - 12/11/2009
Fadil Santosa University of Minnesota 7/1/2008 - 6/30/2010
Arnd Scheel University of Minnesota 9/1/2009 - 6/30/2010
Charles M. Schroeder University of Illinois at Urbana-Champaign 12/6/2009 - 12/11/2009
George R Sell University of Minnesota 9/1/2009 - 6/30/2010
Tsvetanka Sendova University of Minnesota 9/1/2008 - 8/31/2010
Shuanglin Shao University of Minnesota 9/1/2009 - 8/31/2010
Eric S. G. Shaqfeh Stanford University 12/6/2009 - 12/11/2009
Amy Shen University of Washington 12/6/2009 - 12/11/2009
John D. Sherwood University of Cambridge 12/5/2009 - 12/11/2009
Zuzanna S. Siwy University of California, Irvine 12/8/2009 - 12/11/2009
Daniel Spirn University of Minnesota 9/8/2009 - 6/1/2010
Todd Squires University of California, Santa Barbara 12/4/2009 - 12/10/2009
Paul H. Steen Cornell University 10/15/2009 - 12/15/2009
Derek Stein Brown University 12/6/2009 - 12/11/2009
Panagiotis Stinis University of Minnesota 9/1/2009 - 6/30/2010
Brian D. Storey Franklin W. Olin College of Engineering 12/6/2009 - 12/11/2009
Huan Sun Pennsylvania State University 8/16/2009 - 12/15/2009
Vladimir Sverak University of Minnesota 9/1/2009 - 6/30/2010
Ulrich Tallarek Philipps-Universität Marburg 12/5/2009 - 12/11/2009
Mark Taylor Sandia National Laboratories 9/1/2009 - 12/18/2009
Jean-Luc Thiffeault University of Wisconsin 9/1/2009 - 6/30/2010
Joel Thomas University of Minnesota 12/7/2009 - 12/11/2009
Burt S. Tilley Worcester Polytechnic Institute 12/6/2009 - 12/9/2009
Chad Michael Topaz Macalester College 9/1/2009 - 6/30/2010
Nathan Totz University of Michigan 12/8/2009 - 12/12/2009
Lalitha Venkataramanan Schlumberger-Doll 12/17/2009 - 12/18/2009
Petia M. Vlahovska Dartmouth College 12/4/2009 - 12/11/2009
Changyou Wang University of Kentucky 9/1/2009 - 6/15/2010
Sijue Wu University of Michigan 9/1/2009 - 6/5/2010
Wei Xiong University of Minnesota 9/1/2008 - 8/31/2010
Jin Xu Shanghai University of Traditional Chinese Medicine 12/9/2009 - 6/9/2010
Xiaochuan Yang Massachusetts Institute of Technology 12/5/2009 - 12/11/2009
Ehud Yariv Technion-Israel Institute of Technology 12/6/2009 - 12/12/2009
Minami Yoda Georgia Institute of Technology 12/7/2009 - 12/11/2009
Tsuyoshi Yoneda University of Minnesota 9/4/2009 - 8/31/2010
Gilad Yossifon Technion-Israel Institute of Technology 12/6/2009 - 12/10/2009
Boris Zaltzman Jacob Blaustein Institute for Desert Research 12/4/2009 - 12/11/2009
Weigang Zhong University of Minnesota 9/8/2008 - 8/31/2010
Yongcheng Zhou Colorado State University 12/6/2009 - 12/11/2009
Legend: Postdoc or Industrial Postdoc Long-term Visitor

IMA Affiliates:
Arizona State University, Boeing, Corning Incorporated, ExxonMobil, Ford, General Motors, Georgia Institute of Technology, Honeywell, IBM, Indiana University, Iowa State University, Kent State University, Korea Advanced Institute of Science and Technology (KAIST), Lawrence Livermore National Laboratory, Lockheed Martin, Los Alamos National Laboratory, Medtronic, Michigan State University, Michigan Technological University, Microsoft Research, Mississippi State University, Motorola, Northern Illinois University, Ohio State University, Pennsylvania State University, Portland State University, Purdue University, Rice University, Rutgers University, Sandia National Laboratories, Schlumberger Cambridge Research, Schlumberger-Doll, Seoul National University, Siemens, Telcordia, Texas A & M University, University of Central Florida, University of Chicago, University of Cincinnati, University of Delaware, University of Houston, University of Illinois at Urbana-Champaign, University of Iowa, University of Kentucky, University of Maryland, University of Michigan, University of Minnesota, University of Notre Dame, University of Pennsylvania, University of Pittsburgh, University of Tennessee, University of Wisconsin, University of Wyoming, US Air Force Research Laboratory, Wayne State University, Worcester Polytechnic Institute