Effect Of Particle Interactions Research Articles

Multiscale damage modeling with the “Morphological Approach” to highlight particle size and interaction effects in highly-filled particulate composites

Abstract This paper concerns the modeling of interfacial damage in highly-filled particulate composites (e.g. solid propellants), thanks to a specific multi-scale approach recently developed, called “Morphological Approach”. This approach was shown to provide both the homogenized and local responses of the composite taking into account heterogeneity of the strain field within the matrix. In this paper, the M.A. ability to deal with particle size and complex interaction effects expected in highly-filled composites is studied. Considering for simplicity the constituents (particles and matrix) as linear elastic, numerical computations are performed on simple periodic microstructures, monomodal random microstructures and finally a bimodal random microstructure. Particle/matrix debonding chronology is analyzed with respect to the particle size as well as the influence of interactions between particles. The role of interfaces orientation is also addressed. The M.A. is shown to account for preferential damage on the largest particles. Moreover, M.A. estimates show that the more important the particle volume fraction, the earlier the first nucleations. Results are in accordance with experimental studies and full-field simulations available in the literature.

Electrophoretic mobility and electric conductivity in suspensions of charge-regulating porous particles

The electrophoresis and electric conduction in a homogeneous suspension of charge-regulating porous spheres such as polyelectrolytes with uniformly distributed ionogenic functional groups and hydrodynamic resistance segments in an arbitrary electrolyte solution are analyzed. The charge regulation relationship between the local fixed-charge density and electric potential because of association and dissociation reactions of the functional groups is linearized and a unit cell model allowing the overlap of the electric double layers of adjacent particles is employed to take account of the effect of particle interactions under an applied electric field. The equilibrium and perturbed electric potential distributions are ascertained by solving the linearized Poisson-Boltzmann equation, whereas the external and internal fluid velocity fields are determined by solving the modified Stokes and Brinkman equations, respectively. Explicit formulas for the mean electrophoretic mobility of the particles and the effective electric conductivity of the suspension are obtained. The variation in the concentration of the charge-determining ions in the bulk solution can cause a reversal in the direction of the electrophoretic velocity and in the difference of the electric conductivity from its reference value for a suspension of neutral porous particles. The magnitude of the electrophoretic mobility decreases with increases in the volume fraction and resistance parameter of the porous particles, but the electric conductivity in general is not a monotonic function of the particle volume fraction.

Diffusiophoresis in suspensions of charged porous particles.

An analysis of the diffusiophoretic motion in a suspension of charged porous spheres in an electrolytic solution with a macroscopic concentration gradient is presented. Each porous particle can be a solvent-permeable and ion-penetrable charged floc or polyelectrolyte molecule, in which the densities of the fixed charges and frictional segments are constant, surrounded by an arbitrary electric double layer. The multiparticle interaction effects are considered through the use of a unit cell model, which allows the overlap of adjacent double layers. The differential equations governing the electric potential, ionic concentration, and fluid velocity distributions inside and outside the porous particle in a unit cell are linearized by assuming that the system is only slightly deviated from equilibrium and then solved as power expansions in its dimensionless fixed-charge density. A closed-form expression for the diffusiophoretic velocity of the porous particle correct to the second order of the fixed charge density is obtained from a balance between the electrostatic and hydrodynamic forces acting on it. Detailed comparisons of the results for the multiparticle diffusiophoresis obtained from the cell model with various boundary conditions are made. The effect of particle interactions on the diffusiophoresis, which is a linear combination of electrophoresis and chemiphoresis, can be significant and complicated in typical situations. Although the electrophoretic mobility of the particles decreases with an increase in the particle volume fraction, their chemiphoretic mobility is not necessarily a monotonic function of it.

Effects of particle size and particle interactions on scheelite flotation

Effects of size distribution (particle size and content of fine fraction (<10 μm)) on scheelite flotation were studied using flotation tests and theoretical calculations. The results show that particle size influences the scheelite recovery and the performance of combined reagents. The scheelite recovery is lowered by adding fine particles (<10 μm) into the pulp containing coarse particles. Extended DLVO (EDLVO) theory confirms that the fine fractions (<10 μm) could interface with the coarse fractions. The interaction energy and fluid forces are relative to the particle size, which might explain why the fine fractions influence the scheelite flotation. The highest recovery of scheelite using combined reagents as collector and optimum ratio of combined reagents were determined by scheelite particle size and reagent performance. However, the optimum adding order was only determined by reagent performance, which has nothing to do with particle size.

Making sense of Brownian motion: colloid characterization by dynamic light scattering.

Dynamic light scattering (DLS) has evolved as a fast, convenient tool for particle size analysis of noninteracting spherical colloids. In this historical review, we discuss the basic principle, data analysis, and important precautions to be taken while analyzing colloids using DLS. The effect of particle interaction, polydispersity, anisotropy, light absorption, and so forth, on measured diffusion coefficient is discussed. New developments in this area such as diffusing wave spectroscopy, particle tracking analysis, microrheological studies using DLS, and so forth, are discussed in a manner that can be understood by a beginner.

Theoretical and experimental examination of particle–particle interaction effects on induced dipole moments and dielectrophoretic responses of multiple particle chains

Dielectrophoresis (DEP), an electrokinetic phenomenon based on particle polarizations in nonuniform electric fields, is increasingly employed for particle and cell characterizations and manipulations in microdevices. However, particle number densities are rarely varied and particle-particle interactions are largely overlooked, but both affect particle's effective polarizations by changing the local electric field, which directly impacts particle assembly into chains. This work examines theoretical and experimental particle-particle interactions and dielectrophoretic responses in nonuniform electric fields, then presents individual and chain velocities of spherical polystyrene microparticles and red blood cells (RBCs) under DEP forces in a modified quadruple electrode microdevice. Velocities are independently compared between 1, 2, 3, and 4 polystyrene beads and RBCs assembled into chains aligned with the electric field. Simulations compared induced dipole moments for particles experiencing the same (single point) and changing (multiple points) electric fields. Experiments and simulations are compared by plotting DEP velocities versus applied signal frequency from 1 kHz to 80 MHz. Simulations indicate differences in the DEP force exerted on each particle according to chain position. Simulations and experiments show excellent qualitative agreement; chains with more particles experienced a decrease in the DEP response for both polystyrene beads and RBCs. These results advance understanding of the extent that induced dipole polarizations with multiple particle chains affect observed behaviors in electrokinetic cellular diagnostic systems.

Simulated study of plasmonic coupling in noble bimetallic alloy nanosphere arrays

The plasmonic coupling between the interacting noble metal nanoparticles plays an important role to influence the optical properties of arrays. In this work, we have extended the Mie theory results of our recent communication to include the effect of particle interactions between the alloy nanoparticles by varying interparticle distance and number of particles. The localized surface plasmon resonance (LSPR) peak position, full width at half maxima (FWHM) and scattering efficiency of one dimensional (1D) bimetallic alloy nanosphere (BANS) arrays of earlier optimized compositions i.e. Ag0.75Au0.25, Au0.25Cu0.75 and Ag0.50Cu0.50 have been studied presently by using discrete dipole approximation (DDA) simulations. Studies have been made to optimize size of the nanosphere, number of spheres in the arrays, material and the interparticle distance. It has been found that both the scattering efficiency and FWHM (bandwidth) can be controlled in the large region of the electromagnetic (EM) spectrum by varying the number of interacting particles and interparticle distance. In comparison to other alloy arrays, Ag0.50Cu0.50 BANS arrays (each of particle radius 50 nm) shows larger tunability of LSPR with wide bandwidth (essential condition for plasmonic solar cells).

On the consistency of results arising from different techniques concerning the nature of supported metal oxide (nano)particles. The case of NiO/Al2O3

It is shown that different techniques (XRD, TPR, FE-SEM, IR, visible and UV spectroscopies) reveal the presence of bulk NiO particles in NiO/Al2O3 catalyst precursors at different loadings. This is explained considering both the different properties revealed by the different techniques and the likely different effect of particle size, shape and interaction with the support on these properties. Oxide-like supported particles revealed by XRD and FE-SEM in these and maybe similar catalyst systems may have well different electronic and chemical properties with respect to unsupported bulk particles. Different Ni oxide surface species may give rise to different catalytic behaviors in CO2 methanation and steam reforming of ethanol–phenol mixture.

Particle image velocimetry in viscoelastic fluids and particle interaction effects

Two main assumptions in laser doppler velocimetry and particle image velocimetry (PIV) are that tracer particles are following the flow faithfully and that they are not interacting hydrodynamically or affecting the flow field. It has been shown, however, that particles in polymeric fluids even in low volumetric concentrations (ϕ < 1 % v/v) can interact profoundly because of the viscoelastic nature of the background fluid, leading even to particle chain or string formation. The objective of this study is to determine how these interactions can affect the flow conclusions drawn from PIV measurements. We chose a highly viscoelastic and shear thinning fluid and confirmed that particle string formation does occur rapidly in a simple shear flow of this fluid. Then, we measured via PIV, the fully developed velocity profile in the mid-plane of a square channel over a wide range of particle loadings 0.005–0.2 % v/v. The measurements confirm that despite the chaining process, there is no discernible effect of particle interaction on PIV velocity measurements.

Thermal Treatment of Al2O3, MgO, and CeO2 Granulated Powders by Induction Thermal Plasma: A Numerical Approach

A plasma–particle interactive flow model has been developed for the investigation of plasma temperature, velocity, particle temperature, diameter, and flight path during in-fight thermal treatment of granulated powders – Al2O3, MgO, and CeO2 in induction thermal plasma, taking into account of plasma particle interaction and particle loading effects. In this model, the conservative equations are solved to investigate the influence of feed-rate and particle diameter on the melting behavior of granulated powders and to predict particle trajectories, temperature histories etc. In this paper attention is given to the effects of carrier gas flow-rate, powder feed-rate and secondary gas (oxygen) flow-rate on the particles' final diameter and trajectory for Al2O3, MgO, and CeO2 powders. Results show that the particles diameter after thermal treatment is strongly dependent on the powder feed-rate, oxygen gas flow-rate and carrier gas flow-rate. Among the three types of powders, particle diameter decrement is significant in case of MgO and less significant in case of Al2O3; and the effect of oxygen flow-rate on the particle diameter decrement is significant in case of MgO. Particles trajectories are wider for smaller particles than that of larger particles. Particle temperature is lowest for MgO and highest for Al2O3 particles.

Quantum transport in bipartite lattices via Landau-Zener tunneling

A scheme for directed transport of quantum particles in a static bipartite lattice driven by an ac force, based on a sequence of Landau-Zener transitions, is proposed theoretically. As compared to directed transport in bipartite lattices exploiting the phenomenon of coherent destruction of tunneling recently suggested by Creffield [Phys. Rev. Lett. 99, 110501 (2007)], the present scheme realizes a robust quantum state transport owing to the adiabaticity of the particle transfer. The transport is realized by an external force with a sawtooth profile and does not require modulation of lattice parameters (intersite couplings and energy levels). The effects of lattice disorder and particle interaction on the directed quantum transport are discussed.

Flow of power-law fluids in fixed beds of cylinders or spheres

AbstractAn ensemble average of the equations of motion for a Newtonian fluid over particle configurations in a dilute fixed bed of spheres or cylinders yields Brinkman’s equations of motion, where the disturbance velocity produced by a test particle is influenced by the Newtonian fluid stress and a body force representing the linear drag on the surrounding particles. We consider a similar analysis for a power-law fluid where the stress $\boldsymbol{\tau} $ is related to the rate of strain $ \mathbisf{e} $ by $\boldsymbol{\tau} = 2m \mathop{ \vert \mathbisf{e} \vert }\nolimits ^{n\ensuremath{-} 1} \mathbisf{e} $, where $m$ and $n$ are constants. In this case, the ensemble-averaged momentum equation includes a body force resulting from the nonlinear drag exerted on the surrounding particles, a power-law stress associated with the disturbance velocity of the test particle, and a stress term that is linear with respect to the test particle’s disturbance velocity. The latter term results from the interaction of the test particle’s velocity disturbance with the random straining motions produced by the neighbouring particles and is important only in shear-thickening fluids where the velocity disturbances of the particles are long-ranged. The solutions to these equations using scaling analyses for dilute beds and numerical simulations using the finite element method are presented. We show that the drag force acting on a particle in a fixed bed can be written as a function of a particle-concentration-dependent length scale at which the fluid velocity disturbance produced by a particle is modified by hydrodynamic interactions with its neighbours. This is also true of the drag on a particle in a periodic array where the length scale is the lattice spacing. The effects of particle interactions on the drag in dilute arrays (periodic or random) of cylinders and spheres in shear-thickening fluids is dramatic, where it arrests the algebraic growth of the disturbance velocity with radial position when $n\geq 1$ for cylinders and $n\geq 2$ for spheres. For concentrated random arrays of particles, we adopt an effective medium theory in which the drag force per unit volume in the medium surrounding a test particle is assumed to be proportional to the local volume fraction of the neighbouring particles, which is derived from the hard-particle packing. The predictions of the averaged equations of motion are validated by comparison with simulations of randomly distributed hydrodynamically interacting cylinders.

Direct particle motion and interaction modeling method applied to simulate propellant burn

A direct particle motion and particle interaction modeling method was developed to provide an alternative means of capturing the fundamental phenomena occurring during the burning of propellant grains. Individual propellant grains and other moving components are directly incorporated into the computational domain, removing the need for correlations for particle drag and interaction effects. The motion of the individual particles is calculated from the locally acting fluid induced and collision effect forces and moments. Particle/object interactions are handled through a soft particle collision algorithm. Localized mass and energy sources, accompanied by a shrinking particle size, simulate the effects of the combustion process.The method is applied to the burning of propellant in a two-dimensional planar gun type system. Parametric studies were performed varying the parameters related to the propellant and projectile to explore the capabilities of the current modeling method and to determine the sensitivity of the gas, propellant, and projectile conditions. The model captured the local pressure waves moving between the breech and the bullet base not observed using a bulk effect model. The results also indicated that the conditions in the system that are most sensitive to the burn rate exponent where a 24% increase in the exponent produced a 200% increase in the peak pressure at the breech. The study demonstrated the utility of this new model in exploring in particular the localized phenomena and conditions that develop during the burning of propellant.

Sedimentation velocity and potential in a concentrated suspension of charged soft spheres

An analytical study of sedimentation in a suspension of charged spherical soft particles, each with the structure of a rigid core surrounded by a porous shell, in an electrolyte solution is presented. The porous shell of the particle is treated as a solvent-permeable and ion-penetrable surface layer of finite thickness, in which hydrodynamic frictional segments with fixed charges distribute uniformly. A unit cell model that allows the overlap of the electric double layers of adjacent particles is employed to account for the effect of particle interactions. When the system is slightly distorted from equilibrium, the electrokinetic equations governing the electric potential, ion concentration, and fluid velocity distributions are linearized and solved using a perturbation method with the fixed charge densities of the core surface and porous layer of each soft sphere as the small parameters. Explicit formulas for the sedimentation velocity and potential in the suspension are obtained to the second orders of these fixed charge densities with the relaxation effect of the double layers included. The sedimentation velocity and potential are not necessarily monotonic functions of the volume fraction of the particles; the particle concentration effects are significant, even in dilute suspensions. In the limiting cases, the analytical solutions of the sedimentation velocity and potential for charged soft spheres reduce to those for charged rigid spheres and charged porous spheres. It is shown that a suspension of charged but neutral soft spheres can produce sedimentation potential, and their sedimentation velocity differs from that of the uncharged soft spheres.

A computational and theoretical analysis of falling frequency VLF emissions

Recently much progress has been made in the simulation and theoretical understanding of rising frequency triggered emissions and rising chorus. Both PIC and Vlasov VHS codes produce risers in the region downstream from the equator toward which the VLF waves are traveling. The VHS code only produces fallers or downward hooks with difficulty due to the coherent nature of wave particle interaction across the equator. With the VHS code we now confine the interaction region to be the region upstream from the equator, where inhomogeneity factor S is positive. This suppresses correlated wave particle interaction effects across the equator and the tendency of the code to trigger risers, and permits the formation of a proper falling tone generation region. The VHS code now easily and reproducibly triggers falling tones. The evolution of resonant particle current JE in space and time shows a generation point at −5224 km and the wavefield undergoes amplification of some 25 dB in traversing the nonlinear generation region. The current component parallel to wave magnetic field (JB) is positive, whereas it is negative for risers. The resonant particle trap shows an enhanced distribution function or ‘hill’, whereas risers have a ‘hole’. According to recent theory (Omura et al., 2008, 2009) sweeping frequency is due primarily to the advective term. The nonlinear frequency shift term is now negative (∼−12 Hz) and the sweep rate of −800 Hz/s is approximately nonlinear frequency shift divided by TN, the transition time, of the order of a trapping time.

Achieving high molecular conversion efficiency via a magnetic field pulse train

We investigate the process of production of ultracold molecules in an ultracold bosonic system with particle interaction via designing a magnetic field pulse train near a Feshbach resonance. This technique offers a high conversion efficiency up to 100% by tuning the pulse durations appropriately. The molecular conversion efficiency is related to the duration of each pulse, which can be derived analytically. It is found that the conversion efficiency is insensitive to the first pulse, highly sensitive to the second one, and very insensitive to the third one. The effects of particle interaction on conversion process are discussed as well.

Autostratification in Drying Colloidal Dispersions: Effect of Particle Interactions

When particles differing in size or charge are mixed and cast, vertical segregation is an inevitable phenomenon in the produced films. Apart from the Peclet number, which is the ratio of evaporation to diffusion rates, particle interactions play a crucial role in determining the distribution of particles in the dried films. Trueman et al. (1) developed a model for vertical segregation of particles during drying. Their numerical solution assumed that the chemical potentials were determined entirely by entropy. We report the effect of particle interactions in various systems: (i) charged particles with different Peclet numbers and (ii) charged particles with the same Peclet numbers. An experimental study has also been carried out for particles with Peclet numbers straddling unity; the experimental results conform with the behavior predicted theoretically.

Combined effects of particle interaction and nonlinear sweep on Landau–Zener transition

We investigate the Landau–Zener transition (LZT) of a two-level system with two types of nonlinearity: particle interaction and nonlinear time-dependent energy sweep, both numerically and analytically. Due to the interplay between these two types of nonlinearity, many interesting phenomena in different parameter regions occur, including breakdown of adiabaticity, fade-out of interference phenomenon, and asymmetry of transition probability. The potential experimental observation of transition dynamics in this system is suggested.

Majorana fermions in strongly interacting helical liquids

Majorana fermions were proposed to occur at edges and interfaces of gapped one-dimensional systems where phases with different topological character meet due to an interplay of spin-orbit coupling, proximity-induced superconductivity and external magnetic fields. Here we investigate the effect of strong particle interactions, and show that the helical liquid offers a mechanism that protects the very existence of Majorana edge states: whereas moderate interactions close the proximity gap which supports the edge states, in helical liquids the gap re-opens due to two-particle processes. However, gapless fermionic excitations occur at spatial proximity to the Majorana states at interfaces and may jeopardize their long term Majorana coherence.

Effect of surface particle interactions during pool boiling of nanofluids

The pool boiling characteristics of nanofluids is affected by the relative magnitudes of the average surface roughness and the average particle diameter. In the present work, an attempt has been made to study the interactions between the nanoparticles and the heater surface. The experimental methodology accounts for the transient nature of the boiling phenomena. The boiling curves of electro-stabilized Al 2O 3 water-based nanofluids at different concentrations on smooth and rough heaters and the burn-out heat flux have been obtained experimentally. Extensive surface profile characterization has been done using non-intrusive optical measurements and atomic force microscopy. A measure of the surface wettability has been obtained by determining the advancing contact angle. These results give an insight into the relative magnitudes of dominance of the prevalent mechanisms under different experimental conditions. Boiling on nanoparticle coated heaters has been investigated and presented as an effective solution to counter the disadvantageous transient boiling behavior of nanofluids.