Sodium salicylate (NaSal) is added to aqueous solutions of cetyl trimethylammonium bromide (CTAB) to convert spherical micelles to wormlike micelles, thus producing an effective drag-reducing agent. A theoretical understanding of why NaSal is so effective at causing this transformation has not been developed at this time. Using a model that combines aspects of free energy models with simulations, we show change in ordering of the amphiphiles within the micelles of different curvatures. The way NaSal transforms the spherical micelles to wormlike micelles is by insertion of the salicylate ion into the surfactant shell, which reduces the preferred mean curvature of the surfactant shell and thus causes the transformation. This mechanism is different from that of a counterion shell formed in the presence of electrolytes. These models help us to understand the interactions between amphiphiles and additives in the micellar headgroups. The results of this model agree with some experimentally observed trends and help to account for others. Comparisons of our models with predictions based only on free energy models highlight the significance of accounting for intramicellar ordering in calculating micelle free energies. In general, such a model can predict the effect of the inclusion of other organic additives into micellar structures.

This paper provides an overview on separation of micron and submicron sized biological (cells, yeast, virus, bacteria, etc.) and nonbiological particles (latex, polystyrene, CNTs, metals, etc.) by dielectrophoresis (DEP), which finds wide applications in the field of medical and environmental science. Mathematical models to predict the electric field, flow profile, and concentration profiles of the particles under the influence of DEP force have also been covered in this review. In addition, advancements made primarily in the last decade, in the area of electrode design (shape and arrangement), new materials for electrode (carbon, silicon, polymers), and geometry of the microdevice, for efficient DEP separation of particles have been highlighted.

This paper presents a numerical study of flow through static random assemblies of monodisperse, spherical particles. A lattice Boltzmann approach based on a two relaxation time collision operator is used to obtain reliable predictions of the particle drag by direct numerical simulation. From these predictions a closure law F (Re p , ϕ) of the drag force relationship to the bed density ϕ and the particle Reynolds number Re p is derived. The present study includes densities ϕ ranging from 0.01 to 0.35 with Re p ranging up to 300, that is compiled into a single drag correlation valid for the whole range. The corelation has a more compact expression compared to others previously reported in literature. At low particle densities, the new correlation is close to the widely-used Wen & Yu -correlation.Recently, there has been reported a discrepancy between results obtained using different numerical methods, namely the comprehensive lattice Boltzmann study of Beetstra et al. (2007) and the predictions based on an immersed boundary -pseudo-spectral Navier-Stokes approach (Tenneti et al., 2011). The present study excludes significant finite resolution effects, which have been suspected to cause the reported deviations, but does not coincide exactly with either of the previous studies. This indicates the need for yet more accurate simulation methods in the future.

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