Stabilization of Ion Concentration Polarization Using a Heterogeneous Nanoporous Junction

We demonstrate a recycled ion-flux through heterogeneous nanoporous junctions, which induce stable ion concentration polarization with an electric field. The nanoporous junctions are based on integration of ionic hydrogels whose surfaces are negatively or positively charged for cationic or anionic selectivity, respectively. Such heterogeneous junctions can be matched up in a way to achieve continuous ion-flux operation for stable concentration gradient or ionic conductance. Furthermore, the combined junctions can be used to accumulate ions on a specific region of the device.Korea Research Foundation (Grant MOEHRD: KRF-2007-331-D00040)Korean Science and Engineering Foundation (Grant MOST: R01-2007-000-20675-0)Korea Research Foundation (Grant MOEHRD: KRF-J03000)National Research Foundation of Korea (Grant NRF-2009- 352-D00034)National Institutes of Health (U.S.) (EB005743)National Science Foundation (U.S.). (CBET-0347348

Numerical Simulation of Fluid Flow and Mass Transport in (Electro)Chromatographic Systems

The main goal of this Ph.D. thesis was the development of an advanced numerical approach to simulate mass transport in microfluidic electrokinetic systems. Understanding of the electrokinetic aspects of mass transport in microfluidic systems has a great importance for a relatively new technique in separation science: capillary and microchip electrochromatography. This technique combines the advantages of high-performance liquid chromatography and capillary electrophoresis. Capillary electrochromatography uses the electroosmotic flow generated by a high, external voltage applied to drive the liquid phase through a porous medium. The general mathematical formulation of the problem of the electroosmotic flow includes the description of various phenomena of different nature: hydrodynamics, electrostatics, ion transport, adsorption and dissociation. In addition, actual microfluidic systems employed in electrochromatography demonstrate frequently the extremely intricate morphology associated with their porous structure impeding the numerical treatment. In this work, the electroosmotic flow is modelled by the iterative numerical solution of the coupled Poisson, Nernst-Planck, and Navier-Stokes equations. In order to realize a computational time required for large-scale simulations of mass transport in actual electrochromatographic systems, the developed numerical model was implemented at a parallel high-performance computer and then used to simulate various electrokinetic problems. Chapter 2 contains a brief general theoretical description of mass transport problems in polar liquids, which are typical for applications in electrochromatographic analysis. The behaviour of such liquids can drastically change when an external electric field is applied due to the presence of the electrical double layer at the solid-liquid interface. Chapter 3 describes mainly the lattice-Boltzmann formalism, an alternative approach in computational fluid dynamics, which allows easily to treat geometrically complex boundaries and which is inherently parallel. In this approach the fluid is modelled by particles moving on a regular lattice. At each time step the particles propagate to neighbouring lattice points and re-distribute their velocities in a local collision phase. This method is extended to electrohydrodynamic problems by incorporating in the model the Lorentz force arising from the interaction of electrical charges in the liquid with the applied electric field. In Chapter 4 the results of a number of simulations concerning various aspects of microfluidic electrokinetics are presented and discussed. They follow the description of the algorithm employed for the computer generation of confined random packings of spherical particles. That algorithm is based on an improved Jodrey-Tory procedure and allows to generate fixed beds of spheres with an arbitrary size distribution confined by an arbitrary container, as well as with periodic boundaries. The random sphere packings are further used as a model of particulate packed chromatographic columns. The presented numerical approach allows to obtain complete information concerning the spatial distribution in a modelled system of the flow velocity, electrical potential and species concentrations. In particular, the developed approach permits to evaluate the error related to the application of the apparent slip velocity boundary conditions to quantify differences between velocity fields obtained under different approximations concerning electrical boundary conditions, to study the effect of local variations in the chemical environment (caused by convection) on the surface charge density and final flow velocity field, to investigate the relation between the electroosmotic flow velocity and parameters of an electrokinetic system, such as the zeta-potential, solution concentration and applied electric field. In addition, the presented approach can be used to investigate the transient behaviour of simulated systems, such as the transient hydrodynamic dispersion in packed beds

Int. J. Numer. Meth. Fluids

In this article we are concerned with an extension of the lattice-Boltzmann method for the numerical simulation of three-dimensional electroosmotic flow problems in porous media. Our description is evaluated using simple geometries as those encountered in open-channel microfluidic devices. In particular, we consider electroosmosis in straight cylindrical capillaries with a (non)uniform zeta-potential distribution for ratios of the capillary inner radius to the thickness of the electrical double layer from 10 to 100. The general case of hetergeneous zeta-potential distributions at the surface of a capillary requires solution of the following coupled equations in three dimensions: Navier-Stokes equation for liquid flow, Poisson equation for electrical potential distribution, and the Nernst-Planck equation for distribution of ionic species. The hydrodynamic problem has been treated with high efficiency by code parallelization through the lattice-Boltzmann method. For validation velocity fields were simulated in several microcapillary systems and good agreement with results predicted either theoretically or obtained by alternative numerical methods could be established. Results are also discussed with respect to the use of a slip boundary condition for the velocity field at the surface. Copyright © 2004 John Wiley & Sons, Ltd. [accessed 2013 November 27th

Indications du thalidomide en 2005 et applications dans le traitement de l'érythème noueux lépreux

PARIS-BIUP (751062107) / SudocSudocFranceF

Effective diffusion coefficients in random packings of polydisperse hard spheres from two-point and three-point correlation functions

We evaluate the effective diffusion coefficient Deff in random packings of polydisperse hard spheres with an analytical formula involving the three-point microstructural parameter ζ2. Bulk packings with solid volume fraction between ϕ = 0.54 and ϕ = 0.634 were computer-generated using experimentally determined particle size distributions characterized by different mean particle diameter and associated standard deviation. The parameter ζ2 was calculated from two- and three-point correlation functions S2 and S3, respectively, via an approach based on sampling templates. Results of the asymptotic analysis for S2 and S3 compare favorably with theoretical predictions. Effective diffusivities calculated by the approximate analytical formula are close to those obtained from simulations using a random-walk particle-tracking technique. The values of Deff are affected by the packings' solid volume fraction, the spatial positions of the spheres, and to a far lesser extent by the particles' polydispersity. The proposed numerical approach can be applied to evaluate effective diffusive transport properties of general two-phase materials just from the geometrical information embodied in ϕ and ζ2