A numerical method based on the distributed Lagrange multiplier method (DLM) is developed for the direct simulation of electrorheological (ER) liquids subjected to spatially nonuniform electric field. The flow inside particle boundaries is constrained to be rigid body motion by the distributed Lagrange multiplier method and the electrostatic forces acting on the particles are obtained using the point-dipole approximation. The numerical scheme is verified by performing a convergence study which shows that the results are independent of mesh and time step sizes. The dynamical behavior of ER suspensions subjected to nonuniform electric field depends on the solids fraction, the ratio of the domain size and particle radius, and four additional dimensionless parameters which respectively determine the importance of inertia, viscous, electrostatic particle-particle interaction and dielectrophoretic forces. For inertia less flows a parameter defined by the ratio of the dielectrophoretic and viscous forces, determines the time duration in which the particles collect near either the local maximums or local minimums of the electric field magnitude, depending on the sign of the real part of the Clausius-Mossotti factor. In a channel subjected to a given nonuniform electric field, when the applied pressure gradient is smaller than a critical value, the flow assists in the collection of particles at the electrodes, but when the pressure gradient is above this critical value the particles are swept away by the flow.

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We experimentally study the transient clustering behavior of viable yeast cells in a dilute suspension suddenly subjected to a nonuniform alternating current (AC) electric field of a microelectrode device. The frequency of the applied electric field is varied to identify two distinct regimes of positive dielectrophoresis. In both regimes, the yeast cells eventually cluster at electrodes' edges, but their transient behavior as well as their final arrangement is quite different. Specifically, when the frequency is much smaller than the cross-over frequency, the nearby yeast cells quickly rearrange in well-defined chains which then move toward the electrodes' edges and remain aligned as elongated chains at their final location. However, when the frequency is close to the cross-over frequency, cells move individually toward the regions of collection and simply agglomerate along the electrodes' edges. Our analysis shows that in the first regime both the dielectrophoretic (DEP) force and the mutual DEP force, which arises due to the electrostatic particle-particle interactions, are important. In the second regime, on the other hand, the DEP force dominates.

A numerical scheme based on the distributed Lagrange multiplier (DLM) method is used to simulate the process of separation of particles with different dielectric properties suspended in an electrorheological (ER) fluid and subjected to a nonuniform electric field. The dielectrophoresis induced separation of particles is possible only when the sign of Clausius-Mossoti factor for the particles is different, as in this case the dielectrophoretic force moves them to different regions of the device. The time required for separation of particle in simulations is larger than that given by an order or magnitude analysis because of the formation of particle chains which arise due to the dipole-dipole interactions among the particles and move much more slowly than isolated particles.

In recent years, it has been demonstrated that nanoparticles can be detached and removed from substrates using laserinduced plasma (LIP) shockwaves. While it was experimentally established the effectiveness of the LIP technique for removing nanoparticles in the sub-100nm range, the removal mechanisms were not well-understood. In this article, we introduce a set of particle removal mechanisms based on moment resistance of the particle-substrate bond and discuss their effectiveness and applicability in laser-induced plasma shock nanoparticle removal. The mechanical interactions between nanoparticles and shockwaves are studied by utilizing molecular dynamic simulation approach. The forces and moments acting on nanoparticles are calculated and are related to the detachment mechanisms. It is demonstrated that sub-100nm particles can be detached from various substrates. Experiments and simulations are performed to study the effect of LIP on optical and EUVL/LTEM substrates in terms of substrate damage. Initial experiments and simulations reveal the window of safe operation of LIP and the mechanisms responsible for material alterations if any at close distances of operation of LIP above the substrate.