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The present study uses the dielectrophoresis (DEP) and electrothermal (ET) forces to develop on-chip micromixers and microconcentrators. A microchannel with rectangular array of microelectrodes, patterned either on its bottom surface only or on both the top and the bottom surfaces, is considered for the analysis. A mathematical model to compute electrical field, temperature field, the fluid velocity, and the concentration distributions is developed. Both analytical and numerical solutions of standing wave DEP (SWDEP), traveling wave DEP (TWDEP), standing wave ET (SWET), and traveling wave ET (TWET) forces along the length and the height of the channel are compared. The effects of electrode size and their placement in the microsystem on micromixing and microconcentrating performance are studied and compared to velocity and concentration profiles. SWDEP forces can be used to collect the particles at different locations in the microchannel. Under positive and negative DEP effect, the particles are collected at electrode edges and away from the electrodes, respectively, irrespective of the position, size, and number of electrodes. The location of the concentration region can be shifted by changing the electrode position. SWET and TWET forces are used for mixing and producing concentration regions by circulating the fluid at a given location. The effect of forces can be changed with the applied voltage. The TWDEP method is the better method for mixing along the length of the channels among the four options explored in the present work. If two layers of particle suspension are placed side by side in the channel, triangular electrode configuration can be used to mix the suspensions. Triangular and rectangular electrode configurations can efficiently mix two layers of particle suspension placed side-by-side and one-atop-the-other, respectively. Hence, SWDEP forces can be successfully used to create microconcentrators, whereas TWDEP, SWET, and TWET can be used to produce efficient micromixers in a microfluidic chip. [ABSTRACT FROM AUTHOR]

The effect of electrostatic force on the dynamics, morphologicalevolution,and drainage time of ultrathin liquid bilayers (<100 nm) are investigatedfor perfect dielectric–perfect dielectric (PD–PD) andionic liquid–perfect dielectric (IL–PD) bilayers. Theweakly nonlinear “thin film” equation is solved numericallyto obtain spatiotemporal evolution of the liquid–liquid interfaceresponses to transverse electric field. In order to predict the electrostaticcomponent of conjoining/disjoining pressure acting on the interfacefor IL–PD bilayers, an analytical model is developed usingthe nonlinear Poisson-Boltzmann equation. It is found that IL–PDbilayers with electric permittivity ratio of layers (lower to top),εr, greater than one remain stableunder an applied electric field. An extensive numerical study is carriedout to generate a map based on εrand the initial mean thickness of the lower layer. This map is usedto predict the formation of various structures on PD–PD bilayerinterface and provides a baseline for unstable IL–PD bilayers.The use of an ionic liquid (IL) layer is found to reduce the sizeof the structures, but results in polydispersed and disordered pillarsspread over the domain. The numerical predictions follow similar trendof experimental observation of Lau and Russel. (Lau, C. Y.; Russel,W. B. Fundamental Limitations on Ordered Electrohydrodynamic Patterning; Macromolecules2011, 44, 7746–7751). [ABSTRACT FROM AUTHOR]

Abstract: In this work, removal of naphthenic acid (NA) using micellar enhanced ultrafiltration has been reported using 10,000 cutoff polyethersulfone membrane. Sodium dodecyl sulfate (SDS) has been used as surfactant. Effects of various parameters like pH, surfactant concentration, transmembrane pressure drop, cross flow velocity and electrolyte concentration on the permeate flux and permeate quality have been investigated in detail. In order to increase the permeate flux, potential of external electric field has also been explored. The electric field has been applied in two modes. In mode 1, a step-wise electric field is applied, so that the operating field strength across the membrane increases stepwise. In mode 2, a fixed electric field is applied throughout the experiment. In second mode of operation, about 24% flux enhancement is achieved compared to 14% in mode 1. [Copyright &y& Elsevier]

Abstract: Deformation of a fluid drop, suspended in a second immiscible fluid, under the influence of an imposed electric field is a widely studied phenomenon. In this paper, the system is analyzed numerically to assess its dynamic behavior. The response of the system to a step change in the electric field is simulated for both perfect and leaky dielectric systems, exploring the influence of the fluid, interfacial, and electrical properties on the system dynamics. For the leaky dielectric case, the dynamic build up of the free charge at the interface, including the effects of convection along the interface due to electrohydrodynamic circulation, is investigated. The departure of the system from linear perturbation theory is explained using these dynamic simulations. The present simulations are compared with analytic solutions, as well as available experimental results, indicating that the predictions from the model are reliable even at considerably large deformations. [Copyright &y& Elsevier]

Abstract: Electrokinetic Phenomena in concentrated disperse and colloid systems have been studied employing Spherical Cell Approach for over three decades. The critical review of the advances in this area, which is conducted in the present paper, demonstrates a number of contradictions between the results reported by different authors. These contradictions are largely associated with imposition of boundary conditions at the outer boundary of the representative Spherical Cell. In order to establish a correct version of the Spherical Cell Approach, in the present paper, the theory of Electrokinetic Phenomena in concentrated suspensions is revisited by primarily focusing on the boundary conditions employed at the Spherical Cell outer boundary. To this end, a general mathematical problem is formulated for addressing the behavior of a planar layer of a macroscopically homogeneous disperse system under simultaneous influence of the pressure difference, gravitation and applied electric fields. On the basis of the general problem formulation, we present strict definitions of the kinetic coefficients which describe the system behavior. Making use of such definitions, some general relationships are rederived for the kinetic coefficients, namely, the Smoluchowski asymptotic expressions and the Onsager irreversible thermodynamic relationships. The general problem is reformulated for describing the electric, hydrodynamic and ion concentration fields inside the representative Spherical Cell. Using an original approach, a complete set of the boundary conditions is derived by employing the only assumption: the average over the disperse system volume is equal to the average over a representative Spherical Cell volume. A general method for predicting the kinetic coefficients is developed by employing the solution of the formulated problem. The developed method is combined with the method of small perturbation parameter using the normalized zeta potential. Final expressions for the kinetic coefficients are obtained while accounting for the terms proportional to zeta potential. The predictions are compared with results of other publications. On this basis, conclusions are made about the validity of different models proposed in the literature. [Copyright &y& Elsevier]