Effect Of Particle Volume Fraction Research Articles

A theoretical hydrodynamic modification on the soil texture analyses obtained from the hydrometer test

The hydrometer test is one of the most reliable approaches to estimate the particle size distribution of fine-grained soil. The general approach neglects the particle hydrodynamic interactions which are known to hinder the settling rate of particles, and, as such, generally leads to an underestimation of the particle diameters. In this study, a theoretical hydrodynamic correction of the hydrometer test is proposed to account for the hindered velocity of particles settling through a suspension of monomodal spherical or non-spherical particles. The polydisperse nature of soil samples is then taken into consideration by introducing an effective volume fraction of particles for each partially sorted monomodal layer of particles. Using this approach, a model to correct for particle hydrodynamic interactions in conventional hydrometer tests is provided and tested successfully against results from laser diffraction measurements.

Theoretical Insight into Dispersion of Silica Nanoparticles in Polymer Melts.

Silica nanoparticles dispersed in polystyrene, poly(methyl methacrylate), and poly(ethylene oxide) melts have been investigated using a density functional approach. The polymers are regarded as coarse-grained semiflexible chains, and the segment sizes are represented by their Kuhn lengths. The particle-particle and particle-polymer interactions are calculated with the Hamaker theory to reflect the relationship between particles and polymer melts. The effects of particle volume fraction and size on the particle dispersion have been quantitatively determined to evaluate their dispersion/aggregation behavior in these polymer melts. It is shown that theoretical predictions are generally in good agreement with the corresponding experimental results, providing the reasonable verification of particle dispersion/agglomeration and polymer depletion.

Breakdown of deterministic lateral displacement efficiency for non-dilute suspensions: A numerical study

We investigate the effect of particle volume fraction on the efficiency of deterministic lateral displacement (DLD) devices. DLD is a popular passive sorting technique for microfluidic applications. Yet, it has been designed for treating dilute suspensions, and its efficiency for denser samples is not well known. We perform 3D simulations based on the immersed-boundary, lattice-Boltzmann and finite-element methods to model the flow of red blood cells (RBCs) in different DLD devices. We quantify the DLD efficiency in terms of appropriate “failure” probabilities and RBC counts in designated device outlets. Our main result is that the displacement mode breaks down upon an increase of RBC volume fraction, while the zigzag mode remains relatively robust. This suggests that the separation of larger particles (such as white blood cells) from a dense RBC background is simpler than separating smaller particles (such as platelets) from the same background. The observed breakdown stems from non-deterministic particle collisions interfering with the designed deterministic nature of DLD devices. Therefore, we postulate that dense suspension effects generally hamper efficient particle separation in devices based on deterministic principles.

A physically-based plastic constitutive model considering nanoparticle cluster effect for metal matrix nanocomposites

As a type of emerging nanomaterials, lightweight metal matrix nanocomposites (MMNCs) with enhanced strength are becoming more and more attractive in recent years. However, nano-sized ceramic particles tend to form clusters during processing. In this paper, we established a physically-based plastic constitutive model to consider the detrimental effect of nanoparticle clusters on strength of MMNCs. We amended the particle size in the constitutive model with an equivalent size of both dispersed and clustered nanoparticles, which was deduced by introducing a probability density function of random distribution and a clustering extent function of nanoparticles. The model was validated by the data from literatures. The model was applied to determine important variables to improve the mechanical properties of MMNCs, including the effects of particle volume fraction, particle size, temperature, and strain rate sensitivities on the strength and flow stress of MMNCs. The model suggests that there exists a maximum strength in MMNCs versus the volume fraction of nanoparticles due to the cluster effect since it is very difficult for current processing techniques to achieve a perfectly uniform dispersion of nanoparticles in MMNCs.

Study of the effect of particle volume fraction on the microstructure of magnetorheological fluids using ultrasound: Transition between the strong-link to the weak-link regimes

The effect of particle volume fraction on the microstructure of magnetorheological (MR) fluids has been studied using ultrasonic techniques. When no magnetic field is applied, they behave as slurry. However, when magnetic field is applied, important features regarding the change of the microstructure have been found with the help of ultrasonic waves propagating in the direction of the magnetic field. As the volume fraction increases, a rearrangement of particles which decrease the compressibility of the system is detected; nevertheless, the material behaves as a non-consolidated material. Three different particle volume fraction regions are found identifying a critical particle volume fraction predicted in the literature. Ultrasounds are confirmed as an interesting tool to study MR fluids in static conditions.

Analysis of multiaxial properties of carbon nanotubes/polypropylene and nanocrystalline cellulose/polypropylene composites

Using the beam element to simulate single wall carbon nanotube (SWCNT) and nanocrystalline cellulose (NCC), finite element method is adopted to perform multi‐axial numerical tests to compare SWCNT and NCC reinforced polypropylene (PP). As a first step, SWCNT and NCC are assumed to be isotropic and linear elastic materials, while PP is assumed to be linear elastic or elastic–plastic. Using the same reinforcement volume fraction, the elastic and elastic–plastic properties of the nanocomposites are compared under biaxial and triaxial loading conditions. Then, the effect of particle volume fraction and particle size is presented. When NCC and SWCNT have equal particle length and number but different particle diameter, both can produce similar improvement on biaxial mechanical properties. Finally, NCC and SWCNT are compared from an economic point of view to get similar mechanical performance (biaxial properties). The results show that NCC is about 646 times cheaper than SWCNT and is an interesting prospect for future work. POLYM. COMPOS., 37:1180–1189, 2016. © 2014 Society of Plastics Engineers

Formation of Soft NanoparticlesviaPolyelectrolyte Complexation: A Viscometric Study

This paper describes the formation of soft nanoparticles resulting from electrostatically driven complexation of oppositely charged polyelectrolytes. The system was composed of a strong polyanion (polystyrene sulfonate, PSS) and a weak polycation (poly(allylamine) hydrochloride, PAH) in large excess. Soft nanoparticles were obtained by pouring a PSS solution into a PAH one under constant stirring. The polyelectrolyte complexes (PEC) were characterized through a viscometric study complemented by Dynamic Light Scattering (DLS), electrophoretic mobility and suspension turbidity measurements. PEC suspensions were centrifuged and by measuring the viscosity of the supernatant, we were able to estimate the free polycation concentration and hence the percentage of complexed polycation. We also measured the relative viscosity of the suspensions; from the estimated contribution of the PEC particles and of the polycation in excess, the average particle volume fraction was estimated. From all viscometric data, we could derive the evolution of the binding stoichiometry in PEC and of the effective particle volume fraction as a function of the mixing ratio (ratio of the cationic to anionic groups) and of the pH. Our results emphasize the importance of charge accessibility in controlling both the stoichiometry and packing density of the complexes.

Simulated and actual micro-structure models on the indentation behaviors of particle reinforced metal matrix composites

This study investigates effects of particle volume fraction and size on the indentation behavior of Al 1080/SiC particle reinforced metal matrix composites based on both 2D simulated and actual micro-structure models using the non-linear finite element method. A simulated micro-structure model assumes randomly distributed square-shaped reinforcements through a matrix while the actual micro-structure model has a reinforcement distribution similar to an actual micro-structure taken from the section of a produced specimen. The equivalent stress and strain distributions as well as the indentation depths were compared based on both micro-structure models and experiments. Simulated and actual micro-structure models exhibited different stress and strain distributions, especially underneath the indenter. The actual micro-structure resulted in discontinuous equivalent stress and strain distributions underneath the indenter whereas the simulated micro-structure exhibited more continuous distributions. Experimental and predicted indentation depths exhibit similar trends. However, the actual micro-structure model provided an apparent improvement to predict indentation depths by decreasing differences between the experimental and predicted indentation depths as both size and especially volume fraction of the reinforced particles were increased. In general, the indentation depth was increased with decreasing volume fraction of reinforcement and increasing reinforcement particle size. The randomness of reinforcement distribution and actual micro-structure affected permanent indentation surface profiles and depths. The actual micro-structure indicated that irregular particle shape and size and randomness of particle distribution were effective parameters for predicting and understanding the indentation behavior of particle reinforced metal matrix composites.

Wavelength Dependent Haze of Transparent Glass-Particle Filled Poly(Methyl Methacrylate) Composites

Glass particles as filler were incorporated in a poly(methyl methacrylate) matrix. The refractive indexes of both materials match at a wavelength of about 400 nm. The effect of particle volume fraction on the light transmittance and light scattering (haze) in dependence of the refractive index difference was studied. The curve shape of the haze in dependence of the wavelength is comparable to that of the refractive index difference, but the base line of the haze increases with the filling grade. This indicates that there are other scattering or absorbing mechanisms, like defects in the filler binding.

Experimental study on the rheology of anisotropic, flocculated and low volume fraction colloids

In this work, we have investigated rheological behavior of colloids with a low particle volume fraction, and anisotropic and flocculated microstructures through measuring their viscosity and electrical resistance under varying shear rates together with utilizing several relevant characterization methods (i.e., Dynamic Light Scattering, Transmission Electron Microscopy, Atomic Force Microscopy, and Capacitance and Electrical resistance measurements). The colloids are formed through the suspension of hydrophilic/phobic fumed silica particle with attractive/repulsive interaction in polyethylene glycol and/or ethylene oxide-propylene oxide copolymer. It is observed that studied suspensions display shear thickening/thinning flow behavior depending on their microstructure (the spatial distribution and arrangements of particles in continuous media) and associated changes in cluster sizes, which are controlled by the break down of densified clusters (due to the shear induced mechanical and hydrodynamical forces) and the interaction forces among particleparticle and particles-polymers (owing to physicochemical effects). The detailed evaluation of the experimental results indicates that the shear thickening phenomena in low volume fraction, anisotropic and flocculated systems can be mainly attributed to the increase in the effective volume fraction of particles due to both hydrodynamic and physicochemical forces.

Dynamic viscoelastic modeling of magnetorheological elastomers

A micromechanics-based viscoelastic constitutive model is proposed to estimate the zero-magnetic-field- and magnetic-field-dependent dynamic shear stiffness and damping behavior for magnetorheological elastomers (MREs). The effect of imperfect interfacial condition between the ferromagnetic particles and the elastomeric matrix on those properties is incorporated in the proposed model. A concept of effective volume fraction of particles is introduced to take into account the particle agglomeration in MREs. The magnetic dipole interaction is further employed to evaluate the magnetic-field-induced increase in shear stiffness of MREs. Numerical simulations are conducted and compared with experimental data to verify the proposed model.

An Improved Efficient Network Model for Determining the Effective Thermal Conductivity of Particulate Thermal Interface Materials

Thermal interface materials (TIMs) are particulate composite materials widely used in the microelectronics industry to reduce the thermal resistance between the device and heat sink. Predictive modeling using fundamental physical principles is critical to developing new TIMs since it can be used to quantify the effect of particle volume fraction and arrangements on the effective thermal conductivity. The existing analytical descriptions of thermal transport in particulate systems do not accurately account for the effect of interparticle interactions, especially in the intermediate volume fractions of 30–80%. An efficient random network model (RNM) that captures the near-percolation transport in these particle-filled systems, taking into account the interparticle interactions and random size distributions, was previously developed by Kanuparthi et al. The RNM approach uses a cylindrical region to approximate the thermal transport within the filler particles and to capture the interparticle interactions. However, this approximation is less accurate when the polydispersivity of the particulate system increases. In addition, the accuracy of the RNM is dependent on the parameters inherent in an analytical description of thermal transport between two spherical particles and their numerical approximation into the network model. In the current paper, a novel semispherical approximation to the conductance of the fillers is presented as an alternative to the cylindrical region approximation used earlier. Compared with the cylindrical model, the thermal conductivities of the semispherical model are more closely to the finite element (FE) results. Based on the FE analysis, the network model is improved by developing an approximation of the critical cylindrical region between two spherical particles over which energy is transported. Comparing the RNM results with FE results and experimental data, a linear relationship of the critical parameter with the thermal conductivity ratio and the volume fraction was found that provides a more accurate prediction of the effective thermal conductivity of the particulate TIMs.

Kappa carrageenan fluid gel material properties. Part 2: Tribology

Semi-solid and liquid food thickeners typically take the form of either polymeric or particulate structures. These structures are known to control flow properties and mixing efficiency which can influence performance, texture and the perception of tastants and aromas. However, their structural influence on thin-film rheology (tribology), which is also relevant for texture perception, is not so well understood. In this investigation, the tribology in a boundary regime of lubrication is tested using kappa carrageenan lubricants formulated both in solution and as gelled particles in suspension (fluid gels) to provide new insights into the structural influence of thickener type on tribology. Polymeric lubricated systems were shown to be dominated by elastic deformation of the tribo surfaces and particulate suspensions were dominated by particles acting as contacting asperities of the mating surfaces. The tribology of gelled particles was shown to depend strongly on particle elasticity where less deformable (stiffer) particles reduce surface–surface contact and therefore reduce friction coefficients. The effect of particle volume fraction on friction coefficient is related to the number of particles entraining the contact and not particle–particle interactions or bulk rheological behaviour.

Slow Motion of a Porous Cylindrical Shell in a concentric cylindrical cavity

This paper concerns the Slow Motion of a Porous Cylindrical Shell in a concentric cylindrical cavity using particle-in-cell method. The Brinkman’s equation in the porous region and the Stokes equation for clear fluid in their stream function formulations are used. The hydrodynamic drag force acting on each porous cylindrical particle in a cell and permeability of membrane built up by cylindrical particles with a porous shell are evaluated. Four known boundary conditions on the hypothetical surface are considered and compared: Happel’s, Kuwabara’s, Kvashnin’s and Cunningham’s (Mehta-Morse’s condition). Some previous results for hydrodynamic drag force and dimensionless hydrodynamic permeability have been verified. Variation of the drag coefficient and dimensionless hydrodynamic permeability with permeability parameter σ, particle volume fraction γ has been studied and some new results are reported. The flow patterns through the regions have been analyzed by stream lines. Effect of particle volume fraction γ and permeability parameter σ on flow pattern is also discussed. In our opinion, these results will have significant contributions in studying, Stokes flow through cylindrical swarms.

Effects of Particle Volume Fraction and Surface Modifiers on Narrow Gap Filling by Liquid Epoxy Resins Containing Silica Particles

Effects of Particle Volume Fraction and Surface Modifiers on Narrow Gap Filling by Liquid Epoxy Resins Containing Silica Particles

Interaction of a planar shock wave with a dense particle curtain: Modeling and experiments

The interaction of a planar shock wave with a dense particle curtain is investigated through modeling and experiments. The physics in the interaction between a shock wave with a dense gas-particle mixture is markedly differently from that with a dilute mixture. Following the passage of the shock wave, the dense particle curtain expands rapidly as it propagates downstream and pressures equilibrate throughout the flow field. In the simulations, the particles are viewed as point-particles and are traced in a Lagrangian framework. A physics-based model is then developed to account for interphase coupling. Compared to the standard drag law, four major improvements are made in the present interphase coupling model to take into account: (1) unsteady force contributions to particle force; (2) effect of compressibility on hydrodynamic forces; (3) effect of particle volume fraction on hydrodynamic forces; (4) effect of inter-particle collision. The complex behavior of the dense particle curtain is due to the interplay between two-way coupling, finite particle inertia, and unsteady forces. Incorporation of these effects through significant modeling improvements is essential for the simulation results to agree well with the experimental data. As a result of the large pressure gradient inside the particle curtain, the unsteady forces remain significant for a long time compared to the quasi-steady force and greatly influence the particle curtain motion.

Characterisation of Al–B4C composite microstructures and their effect on fluidity

Microstructural variables such as particle volume fraction, distribution and agglomeration significantly affect the properties of Al–B4C metal matrix composites. The aim of the investigation was to study the quantitative characterisation of the microstructural variables and their effects on the fluidity of the composites. The results showed that the particle volume fraction, homogeneity of particle distribution, and volume fraction of agglomerates could be quantitatively analysed by the imaging analysis technique. It was found that the amounts of the particle clusters and networks, as well as the effective volume fraction of total particles augmented with the increase in the holding time. In addition, the longer holding time was, the less homogeneous the particle distribution became. Moreover, the particle agglomerates have a tendency to migrate to the flow end which results in an accelerated stopping of the flow. The increase in the effective particle volume fraction corresponded well with the fluidity deterioration of the composites during the melt holding.Les paramètres microstructuraux, tels que la fraction volumique, la distribution et l’agglomération des particules affectent de manière significative les propriétés du composite à matrice métallique Al–B4C. Ce travail porte sur la caractérisation quantitative des propriétés microstructurales ainsi que leurs effets sur la fluidité des matériaux composites. La fraction volumique des particules, l’homogénéité de leur distribution et la fraction volumique des agrégats ont été analysées quantitativement à l’aide de la technique d’analyse d’images. Les résultats montrent une augmentation de la quantité d’agrégats et de la fraction volumique effective des particules avec l’augmentation du temps de maintien. De plus, plus le temps de maintien est long, moins grande est l’homogénéité de la distribution des particules. Par ailleurs, les agglomérats ont tendance à migrer vers l’aval de l’écoulement, ce qui accélère l’arrêt de l’écoulement. L’augmentation de la fraction volumique effective des particules correspond parfaitement à la dégradation de la fluidité des matériaux composites.

Three-dimensional simulation of microstructure evolution for three-phase nano-composite ceramic tool materials

It is believed that adding particles can improve mechanical properties of ceramic tool materials. So far, two-phase composites materials have been widely investigated. However, materials with two-kinds of particles are seldom researched. In this paper, microstructure evolution of two-phase and three-phase nano-ceramic materials are simulated and compared. The effects of particle volume fraction, radius, distributions and grain boundary energy ratios on microstructure evolution are analyzed respectively. It shows that adding two kinds of particles can receive better grain refinement than just adding one kind of particles. The higher volume fraction and smaller-sized nano-particles have stronger pinning force on matrix grain growth. The nano-particles located around grain boundaries have better inhibition effect than those distributed randomly on matrix grain growth. Grain boundary energy ratio has significant influence on pinning effect of particles. The nano-particles not only restrain grain boundary migration, but also prevent the elimination of small grains and refine matrix grains.

Combined numerical/experimental investigation of particle diameter and interphase effects on coefficient of thermal expansion and young's modulus of SiO2/epoxy nanocomposites

AbstractA combined numerical/experimental approach is used to study the effects of the particle/matrix interphase on the coefficient of thermal expansion (CTE) and Young's modulus of SiO2/epoxy nanocomposites having nanoparticle reinforcements of different sizes. Our experiments showed that the composite CTE decreases and composite Young's modulus increases with decreasing nanoparticle diameter at the same volume fraction, but our finite element (FE) model predictions did not match the expected trends when the interphase was not accounted for. The new models include an interphase region around the nanoparticle which results in an “effective particle volume fraction” that is larger than the actual particle volume fraction. The results from the models are compared with the experimental results and the new models are accurately fitted to the experimental results using the interphase thickness as a curve‐fitting parameter. We believe that this is the first published report on the use of combined numerical/experimental investigations of both elastic stiffness and thermal expansion characteristics to demonstrate the existence of a particle size‐dependent “effective particle volume fraction” due to the particle/matrix interphase region in a nanoparticle‐reinforced composite. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Thermal conductivity of carbon nanotube nanofluid—Experimental and theoretical study

AbstractIn this work, thermal conductivity of carbon nanotubes' (CNTs) nanofluid is studied both experimentally and theoretically. CNT nanofluids were stabilized using gum arabic (GA). The concentration of CNTs was varied from 0.01–0.1 wt% while the concentration of GA was varied from 1–2.5 wt%, respectively. The effect of particle volume fraction and temperature on the thermal conductivity enhancement of the nanofluids was also studied. A simple thermal conductivity model which demonstrates the effect of diameter and aspect ratio of the CNTs and takes into account the effect of temperature on thermal conductivity enhancement is presented. Good agreement between experimental and estimated values proves that the proposed model can provide precise prediction of the thermal conductivity of fluid containing CNTs. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.20405