Influence Of Polydispersity Research Articles

Effect of pore size polydispersity on the acoustic properties of high-porosity solid foams

This study investigates the influence of pore size polydispersity on the acoustic behavior of high-porosity solid foams using numerical simulations. The effect of the size of the periodic unit cell (PUC) on the transport parameters is first examined. It is found that the size of the PUC required for properly estimating the acoustic properties of random foams depends on both the analyzed transport parameter(s) and level of polydispersity. Assuming identical and constant aperture ratio of membranes, the results indicate that (i) the viscous permeability is a reliable indicator regarding the size of the PUC (a more constraining property than the other transport parameters), and (ii) high-polydispersity foams require a larger number of pores in the PUC to achieve convergence with respect to morphological characteristics and acoustic properties. The influence of polydispersity on dimensionless transport parameters is then analyzed. It is found that polydispersity has a negligible effect on the high-frequency tortuosity but induces substantial variations in the remaining macroscopic parameters. Simulations further show that the ratio of the dimensionless transport parameters does not depend on membrane aperture ratio. This important result allows us to propose a fast method to estimate the acoustic properties of a random foam from the transport parameters of monodisperse foams with different pore sizes, for each studied transport parameter. The proposed method is finally employed to characterize the pore size and polydispersity in two real foams (with and without membranes), solving an inverse problem.

Influence of polydispersity on the relaxation mechanisms of glassy liquids

Influence of polydispersity on the relaxation mechanisms of glassy liquids

Effect of polydispersity in concentrated magnetorheological fluids

Magnetorheological fluids (MRF) are smart materials of increasing interest due to their great versatility in mechanical and mechatronic systems. As main rheological features, MRFs must present low viscosity in the absence of magnetic field (0.1–1.0 Pa.s) and high yield stress (50–100 kPa) when magnetized, in order to optimize the magnetorheological effect. Such properties, in turn, are directly influenced by the composition, volume fraction, size, and size distribution (polydispersity) of the particles, the latter being an important piece in the improvement of these main properties. In this context, the present work aims to analyze, through experiments and simulations, the influence of polydispersity on the maximum packing fraction, on the yield stress under field (on-state) and on the plastic viscosity in the absence of field (off-state) of concentrated MRF (φ = 48.5 vol.%). Three blends of carbonyl iron powder (CIP) in polyalphaolefin oil were prepared. These blends have the same mode, but different polydispersity indexes (α), ranging from 0.46 to 1.44. Separate simulations show that the random close packing fraction increases from about 68% to 80% as the polydispersity indexes increase over this range. The on-state yield stress, in turn, is raised from 30 ± 0.5 kPa to 42 ± 2 kPa (B ≈ 0.57 T) and the off-state plastic viscosity, is reduced from 4.8 Pa.s to 0.5 Pa.s. Widening the size distributions, as is well known in the literature, increases packing efficiency and reduces the viscosity of concentrated dispersions, but beyond that, it proved to be a viable way to increase the magnetorheological effect of concentrated MRF. The Brouwers model, which considers the void fraction in suspensions of particles with lognormal distribution, was proposed as a possible hypothesis to explain the increase in yield stress under magnetic field.

Influence of polydispersity and breakage on stochastic simulations of spray fluidized bed agglomeration

Monte Carlo (MC) model is a stochastic and discrete method to enhance the understating of spray fluidized bed (SFB) agglomeration in the field of food, chemical and pharmaceutical industry. Previous studies focused on agglomerates composed of monodisperse primary particles. Size dispersity of primary particles is, though, an important aspect to fully assess the morphological features of an agglomerate. In the current work, a polydisperse tunable aggregation model is therefore developed. The radius of gyration, porosity, surface area and agglomeration rate increase with primary particle dispersity. Furthermore, the breakage of already formed agglomerates is introduced in the MC model. The influence of breakage decreases the overall growth rate and the arithmetic mean diameter of the particle size distribution by around 11%. The overall growth rate and the diameter of agglomerates with a similar number of primary particles increase with decreasing temperature of fluidization gas and increasing mass fraction of binder.

Polycarboxylate ester adsorption on cement grains: Influence of polydispersity

Although in academic and industrial practice polymers are typically described by their average molecular parameters, most often they display a polydispersity both in size and in properties. In this paper, we focus on the influence of polydispersity on the adsorption of polycarboxylate ester on cement grains and on its influence on the definition of a so-called affinity of the polymer to the surface. We first show that a constant fraction of a polydisperse polycarboxylate ester always adsorbs no matter the availability of adsorption sites. We moreover suggest from our measurements and from scaling laws from literature that the degree of polydispersity in the structure of polycarboxylate ester should affect adsorption at both low and intermediate dosages and hydrodynamic radii in solution. However, it shall not have a major influence on polymer layer thickness or saturation dosage.

The influence of polydispersity on the structural properties of the isotropic phase of magnetic nanoplatelets

By employing a combination of Molecular Dynamics simulations and experimental SAXS studies, we investigate low-concentration suspensions of polydisperse magnetic platelets with dipole moments perpendicular to the platelets' plane. Exploiting the precise control of platelet size and shape in simulation, we are also able to contrast these results with equivalent density monodisperse suspensions. We show how the polydispersity may lead to the reduction of the orientational and spatial correlations in the absence of an applied field, while simultaneously facilitating the field-induced transition into a nematic-like phase. Along with structural properties, we investigate the magnetic response. This allows us to confirm that the inter-platelet magnetic correlations have a negligible influence on the structure of the low-density suspensions.

Modeling the process of cohesive sediment settling and flocculation based on CFD–DEM approach

The settling process of cohesive sediment particles exists universally in nature and many engineering fields. Some of them have negative impacts, e.g., leading to the storage loss of reservoir, prolonging the duration of the reclamation project. Thus, understanding and quantifying cohesive sediments settling and flocculation processes are of great importance. In the present work, a three-dimensional model is applied to investigate the cohesive settling process numerically by computational fluid dynamics–discrete element method (CFD–DEM) approach. In the model, the cohesiveness of the sediment particle is modeled by implementing the van der Waals force. The simulation results are in good agreement with the experimental results, which demonstrate the ability of the current model to study the settling and flocculation process. For cohesive particles, the influence of polydispersity on structural density is discussed in two aspects: (a) the particle mean diameter d50 and (b) the geometric standard deviation d85/d15. Furthermore, the results show that the influence of these two parameters is more profound when a large Hamaker constant is applied. We also study the relationship between the maximum value of structural density and the Hamaker constant. The structure density is found to be significantly influenced by Hamaker constant when Hamaker constant is smaller than $$2.0\, \times \,10^{ - 20} \,{\text{J}}$$ . Besides, for the poly-dispersed system, different from non-cohesive particles, the segregation phenomenon is not obvious for poly-dispersed cohesive particles due to the flocculation phenomenon. Moreover, the excessive pore pressure in sediment bed does not dissipate instantaneously as the non-cohesive sediment bed. And with the increase of the Hamaker constant, the excessive pore pressure dissipation velocity of the sediment bed decreases. In this work, we study the flocculation phenomenon of cohesive particles. It’s found that the influence of cohesive force is more significant on small particles. Since with the reduction of the particle size, the inertial force decreases to a greater extent compared to the cohesive force, the particles’ motion is mainly determined by the cohesive force.

The stochastic effect of polydispersity on polymeric DNA delivery vectors

ABSTRACTThe molecular composition and architecture of polymeric DNA delivery reagents govern their transfection efficiency. One parameter that is understudied is the influence of polydispersity on transfection efficiency. Here we report the synthesis of two molecularly identical polymer series, but with different polydispersities (1.3 vs. 2.0) and quantify the effect polydispersity on transfection efficiency. The results show that the effect of polydispersity on transfection efficiency in cell culture is not predictable and is stochastic in nature. In general terms, polymers with high polydispersity mediated higher levels of transfection in vitro compared to low polydispersity polymers with the same side chain distribution and composition. However, at higher molecular weights, the effect of polydispersity was polymer specific, with enhanced transfection efficiency in some cases, but negligible in others. An interesting outcome is that the higher polydispersity polymers generally enhanced the stability of polymer:DNA complexes and this enhancement generally correlated with enhanced transfection efficiency. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45965.

Influence of polydispersity on the microstructure of frictionless disc packings under simple shear

By means of 2D Contact Dynamics simulations, we explored the effects of the shape and size span of the grain size distribution (GSD) on the microstructure of a sheared granular packing, in terms of its packing fraction and the connectivity of its contact network. We focused on GSDs that can be represented by a power law, which are widely used in several engineering and industrial contexts. The interest in power law GSDs originates in the works of Fuller and Thompson in 1907 and 1919, in which it was found that a maximum density is obtained for a power law GSD with an exponent of 0.5. This disagrees with recent DEM results where the densest packing is obtained for linear cumulative volume distributions. In order to explore this discrepancy, we performed systematic simulations in which we varied both the size span (the ratio between the largest and the smallest diameter) and the exponent (shape) of the distribution. We find that the exponent equal to 0.5 produces the highest density for all size spans. Furthermore, the proportion of rattlers and coordination were also analyzed, showing that the system’s connectivity is strongly affected by both the size span and the shape of the distribution.

Sensitivity analysis of Immersed Boundary Method simulations of fluid flow in dense polydisperse random grain packings

Polydisperse granular materials are ubiquitous in nature and industry. Despite this, knowledge of the momentum coupling between the fluid and solid phases in dense saturated grain packings comes almost exclusively from empirical correlations [2–4, 8] with monosized media. The Immersed Boundary Method (IBM) is a Computational Fluid Dynamics (CFD) modelling technique capable of resolving pore scale fluid flow and fluid-particle interaction forces in polydisperse media at the grain scale. Validation of the IBM in the low Reynolds number, high concentration limit was performed by comparing simulations of flow through ordered arrays of spheres with the boundary integral results of Zick and Homsy [10]. Random grain packings were studied with linearly graded particle size distributions with a range of coefficient of uniformity values (C u = 1.01, 1.50, and 2.00) at a range of concentrations (ϕ ∈ [0.396; 0.681]) in order to investigate the influence of polydispersity on drag and permeability. The sensitivity of the IBM results to the choice of radius retraction parameter [1] was investigated and a comparison was made between the predicted forces and the widely used Ergun correlation [3].

The effect of polydispersity on the magnetostatic properties of concentrated ferrofluids

A statistical model of highly concentrated polydisperse ferrocolloids is proposed. The study approach is based on the second-order modified mean-field theory (MMF2) [A.O. Ivanov, O.B. Kuznetsova, Magnetic properties of dense ferrofluids: an influence of interparticle correlations, Phys. Rev. E 64 (2001) 041405-1–12]. To increase the accuracy of the analytical expression of the magnetization we calculate the contribution of the dipole–dipole interaction energy up to the 2nd order in the pair distribution function for ferroparticles system. The obtained expression of magnetization corresponds to the theoretical expression of initial magnetic susceptibility proposed by the new polydisperse theory [A.O. Ivanov, E.A. Elfimova, Low-temperature magnetic susceptibility of concentrated ferrofluids: the influence of polydispersity, J. Magn. Magn. Matter. 374 (2015) 327–332] exactly. In conjunction it can be applied for magnetogranulometric analysis of polydisperse concentrated ferrofluids.

Influence of polydispersity on the isotropic-nematic boundary in melt of semiflexible diblock copolymer

The analytical expressions have been obtained to describe the dependence of spinodal curve at which isotropic state of polydisperse melt of semiflexible diblock copolymer becomes unstable with respect to formation of nematic state on the polydispersity indices of the blocks, parameters of anisotropic interactions, and flexibility of blocks. The flexibility of blocks is taken into account within discrete worm-like chain model, lengths of blocks are assumed to be distributed by the Schulz–Zimm distribution. It is shown that increase of degree of polydispersity of blocks yields the increase of nematic spinodal temperature.

Microscopic dynamics of an amorphous C60x /C70(1 − x) fullerene mixture

This paper presents the results of investigation of the propagation mechanism of collective excitations in amorphous C60x /C70(1 − x) fullerene mixtures (with equimolar concentration x = 0.50), which were obtained using molecular dynamics simulation. The critical glass-transition temperature of the system T c = 1548 K was determined from the change in the behavior of the Wendt-Abraham parameter. Spectral densities of the time correlation functions of the longitudinal $$\tilde C_L (k,\omega )$$ and transverse $$\tilde C_T (k,\omega )$$ currents for a wide region of wave numbers at temperatures below the glass-transition temperature were calculated. It was found that the dynamics of density fluctuations in amorphous C60x /C70(1 − x) fullerene mixtures is characterized by two dispersion acoustic-like branches of the longitudinal and transverse polarizations. The influence of poly-dispersity and form factor of the molecule of the mixture component on the microscopic dynamics of the density fluctuation in multicomponent systems was established.

Nanoparticle Polydispersity Can Strongly Affect In Vitro Dose

When nanomaterials meet the biological world, the cellular interaction of nanoparticles is routinely assessed in in vitro systems. Establishing dose–response relationships requires that the dose of nanoparticles delivered to the cell is accurate and precise. Nanoparticles as such or coated with high molecular‐weight compounds are rarely uniform and the influence of heterogeneity, including polydispersity both in size and mass density, on the delivered dose is never studied before. Furthermore, a probabilistic term describing particle adherence to cells is introduced and the importance is discussed. By tracing the movement of discrete particles via modeling, it is found that the influence of heterogeneity cannot be neglected when the average particle size promotes settling over diffusion. However, the influence of polydispersity on the delivered cellular dose is less critical for particulate systems whose mean size promotes diffusion. The influence of a non‐instantaneous particle association to the cell is negligible for particles whose motion is dominated by settling, but it is relevant for small particles whose motion is governed by diffusion.

Low-temperature magnetic susceptibility of concentrated ferrofluids: The influence of polydispersity

In this paper we address the question of theoretical explanation of extremely high low-temperature initial magnetic susceptibility of concentrated ferrofluids . These laboratory synthesized samples [A.F. Pshenichnikov, A.V. Lebedev, J. Chem. Phys. 121(11) (2004) 5455; Colloid J. 67(2) (2005) 189] demonstrated the record-breaking values χ ~ 120 – 150 at temperatures ~ 230–240 K. The existing models predict such high susceptibility only under the assumption of unreasonably large dipolar coupling constant, which is out of the range of applicability. Here we calculate the second virial contribution to susceptibility for polydisperse ferrofluid, modeled by the dipolar hard sphere fluid. In the resulting expression there exists the parameter, which plays a part of dipolar coupling constant and which is defined in a form of double averaging of high powers of particle sizes over the granulometric distribution. For real particle size distribution this effective parameter at least twice exceeds the commonly defined polydisperse dipolar coupling constant. We show that the low-temperature magnetic susceptibility of the record-breaking ferrofluids could be explained theoretically on the basis of the first terms of the polydisperse second virial contribution in combination with the second-order modified mean field model. • Record-breaking magnetic susceptibility of ferrofluids at low temperatures. • Second virial contribution to magnetic susceptibility of polydisperse ferrofluids. • Interparticle dipole correlations are more pronounced in dense ferrofluids. • Presented model describes the ferrofluid susceptibility χ ~ 120 at temperature 240 K.

Comparison between theory and simulations for the magnetization and the susceptibility of polydisperse ferrofluids

The influence of polydispersity on the magnetization of ferrofluids is studied based on a previously published magnetization equation of state (Szalai and Dietrich, 2011 J. Phys.: Condens. Matter 23 326004) and computer simulations. The polydispersity of the particle diameter is described by the gamma distribution function. Canonical ensemble Monte Carlo simulations have been performed in order to test these theoretical results for the initial susceptibility and the magnetization. The results for the magnetic properties of the polydisperse systems turn out to be in quantitative agreement with our present simulation data. In addition, we find good agreement between our theory and experimental data for magnetite-based ferrofluids.

Electro-induced orientational ordering of anisotropic pigment nanoparticles

The response of anisotropic pigment particle suspensions to externally applied electric fields has been explored for possible application in reflective display technologies. Three different types of pigment particle were suspended in dodecane, using a polymeric stabilizer, and showed Schlieren textures between crossed polarizers at high concentrations (greater than 25-30 wt%), indicating the formation of colloidal nematic phases. Orientational order parameters were determined by X-ray scattering, and the influence of polydispersity on the values is discussed. X-ray scattering measurements also demonstrated a change in the structure factor consistent with the onset of a colloidal nematic phase. In addition, the pigment particles were dispersed into various liquid crystal hosts at low concentrations (less than 5 wt%) with and without the presence of mesogenic mimic stabilizers. However, the influence of these stabilizers on orientational ordering could not be confirmed. The electro-induced ordering determined via scattering was related to the electro-optical response of each suspension using a simple model. The particles in nematic hosts not only showed a high degree of orientational ordering at lower electric field strengths, but also showed a reduction in stability. Although these systems have shown strong orientational ordering, the optical response has been limited by the intrinsic shape of the pigment particles and the distribution of the transition dipoles moments within them. Nevertheless, the feasibility of developing materials for display applications has been demonstrated.

Accounting for Polydispersion in the Eulerian Large Eddy Simulation of the Two-Phase Flow in an Aeronautical-type Burner

A major issue for the simulation of two-phase flows in engines concerns the modeling of the liquid disperse phase, either in the Lagrangian or the Eulerian approach. In the perspective of massively parallel computing, the Eulerian approach seems to be more suitable, as it uses the same algorithms as the gaseous phase solver. However taking into account the whole physics of a turbulent spray, especially in terms of polydispersity, requires an additional modeling effort. The Mesoscopic Eulerian Formalism (MEF) [13] accounts for the effect of turbulence on the disperse phase, and was extended to the Large Eddy Simulation framework [41], but is limited to monodisperse flows. In [38], the influence of polydispersity on resolved and unresolved turbulent motions of the disperse phase was highlighted, and a first model was proposed, based on size-conditioned statistics. Starting from this idea, a coupling between the MEF and the Multifluid Approach (MA) [30] is proposed. The MA decomposes the Eulerian phase into several fluid classes called sections, and corresponding to size intervals. Each section uses then size-conditioned closures. The original idea of this work is to use the MEF closures independently in each section, taking into account the mean droplet size of this section. This new approach, called Multifluid Mesoscopic Eulerian Formalism (MMEF), is then able to capture polydispersion with associated size-conditioned turbulent dynamics. First, the importance of polydispersity and the ability of MMEF to capture it are highlighted with a 0D evaporation case and a 2D vortex case, showing its impact on dynamics in both size and physical spaces. Then, the MMEF is applied to the MERCATO configuration of ONERA [18]. Results are compared to monodisperse Eulerian, Lagrangian and experimental results.

Influence of polydispersity on micromechanics of granular materials

We study the effect of polydispersity on the macroscopic physical properties of granular packings in two and three dimensions. A mean-field approach is developed to approximate the macroscale quantities as functions of the microscopic ones. We show that the trace of the fabric and stress tensors are proportional to the mean packing properties (e.g., packing fraction, average coordination number, and average normal force) and dimensionless correction factors, which depend only on the moments of the particle-size distribution. Similar results are obtained for the elements of the stiffness tensor of isotropic packings in the linear affine response regime. Our theoretical predictions are in good agreement with the simulation results.

Simulation of heterogeneous end-coupling reactions in polydisperse polymer blends

The influence of polydispersity on the interfacial kinetics of end-coupling and microstructure formation in the melt of immiscible polymers was studied using dissipative particle dynamics simulations. The irreversible reaction started at a flat interface between two layers, each of which contained polymer chains of two different lengths with functionalized or unreactive end groups. As in the case of fully functionalized monodisperse reactants [A. V. Berezkin and Y. V. Kudryavtsev, Macromolecules 44, 112 (2011)], four kinetic regimes were observed: linear (mean field coupling at the initial interface), saturation (decreasing the reaction rate due to the copolymer brush formation or reactant depletion near the interface), autocatalytic (loss of the initial interface stability and formation of a lamellar microstructure), and terminal (microstructure ripening under diffusion control). The interfacial instability is caused by overcrowding the interface with the reaction product, and it can be kinetically suppressed by increasing chain length of the reactants. Main effects of polydispersity are as follows: (i) the overall end-coupling rate is dominated by the shortest reactive chains; (ii) the copolymer concentration at the interface causing its instability can be not the same as in the lamellas formed afterwards; (iii) mean length of the copolymer product considerably changes with conversion passing through a minimum when a microstructure is just formed.