Ideal Packing Research Articles

Polyelectrolyte Microgels at a Liquid-Liquid Interface: Swelling and Long-Range Ordering.

In this work, we studied the behavior of charged microgels at a liquid-liquid interface by means of dissipative particle dynamics simulations with explicit electrostatic interactions; the liquids represent polar and nonpolar solvents like water and oil. The effect of the fraction of charged groups and both solvents qualities on the microgel size, shape, degree of immersion into different liquids, and 2D ordering of the microgels at the interface is studied. For the case of both athermal solvents, we demonstrated that increasing the fraction of charged units results in significant swelling of the microgel inside the polar liquid and a dramatic drop in the number of adsorbed monomer units. For the case of a bad nonpolar solvent for the polyelectrolyte microgels, they easily get detached from the surface into the polar solvent. When the opposite case of a bad polar solvent is considered (like high temperatures for thermosensitive PNIPAM- or PVCL-based microgels), the microgels demonstrate a decrease of the swelling perpendicular to the interface at low χ-values, and they start to swell into the nonpolar liquid at high χ-values. Two approaches for accounting for different dielectric permittivity of the liquids were considered: implicit and explicit ones; we obtained that the results of the two approaches were always in qualitative agreement. However, the explicit model is necessary to correctly reproduce the physics of the phenomena in certain regimes, in particular, when the charged molecules move through the interface of two liquids. Finally, the microgels ordering was studied at the liquid-liquid interface. We found that even at rather low fraction of charged monomer units the microgels exhibit an almost ideal hexagonal packing even though the average distance between the microgels centers is significantly larger than the microgel diameter, while uncharged microgels positions were completely random. This implies that the interfacial ordering can be controlled by using pH-sensitive monomer units in the microgel structure.

A study of packing parameters that influence the fresh properties of self-compacting concrete

Abstract Some known self-compacting concrete (SCC) mix-designs are based on the lowest void content as a purpose of an ideal packing. However, a composition with a lower void content is not a guarantee of good synergy between the largest and smallest grain in the fresh state. The purpose of this study was to identify and evaluate different packing parameters in the aggregates gradations that influence on the self-compactability. Nine aggregates combinations (4 binaries, 4 ternaries and 1 quaternary) were used for determination of nine gradations. Tests as slump-flow, L-box and V-funnel were used. The distribution coefficient (q) was determined by the Alfred model. The results showed that not all values of q (between 0.201 and 0.253) attended the values given for SCC, and the gradations with the lowest difference among the coarse and fine particles, higher void content, continuous distributions and 50% of coarse aggregates had better performance.

Enhancement of Plastering Effect on Strengthening Wellbore by Optimizing Particle Size Distribution of Wellbore Strengthening Materials

Wellbore strengthening materials (WSMs) have been widely used to strengthen the wellbore stability and integrity, especially those lost circulation materials (LCMs) used for mud loss impairment. To enhance the wellbore strengthening effect rather than a loss impairment, plastering effect can be used to increase the fracture gradient of the wall and minimize the probability of inducing new fractures. This is done by smearing the mudcake and pores and forming an internal cake inside the rock matrix using WSMs (or LCMs). Until now, the particle size distribution (PSD) of LCMs have been widely studied for the minimization on the mud loss (e.g., Abran’s rule, ideal packing theory, D90 rule, Halliburton D50 rule, etc.). However, there are few empirical rules focused on the maximum wellbore strengthening effect. This study attempts to find the desired PSD of plastering materials to enhance wellbore stability. In this research, the Brazilian test was used to quantify tensile strength. Meanwhile, the filtration characteristics of WSMs through the rock matrix were observed using a scanning electron microscope (SEM) and an energy-dispersive system (EDS). Finally, this paper adopts D50 of WSMs to be the mean pore throat size for a maximum improvement on the rock tensile strength. We have observed that the closer the D50 of WSMs in the WSMs to the mean pore throat size, the stronger the saturated rock matrix.

Determining random packing density and equivalent packing size of superballs via binary mixtures with spheres

We propose a new approach to determining the random packing densities of superballs via binary mixtures with spheres. The main idea of the approach is to suppress order formations in non-spherical particle packings via the polydispersity of particle shapes, which avoids using order metrics. The packing density of superballs in a mixture can be segregated using a linear fitting method with the concept of equivalent packing size (or size ratio with unit spheres) which represents the effective size (or volume) of a non-spherical particle in a binary mixture with spheres. We systemically study the packing properties of binary mixtures consisting of spheres and superballs and obtain the equivalent packing sizes of superballs. Our results show that the equivalent packing size ratio always corresponds to the minimal packing density or specific volume (reciprocal of packing densities) variation, and is independent of the solid volume fraction. The specific volumes of mixtures with the equivalent packing size ratio are always the upper bound for all the solid volume fractions. The linear relationship between the specific volume and solid volume fraction is only observed in the mixtures with superballs of small surface shape parameters (shapes close to a sphere), which results from the highly disordered nature in the mixtures. Moreover, the ideal random packing densities of mono-sized superballs obtained via the linear fitting method are surprisingly close to those of the MDRPs (maximally dense random packings), further verifying that the MDRPs of non-spherical particles correspond to the ideal random packings whose degrees of order are at the same level with that of the random close packing of spheres. Our work leads to a better understanding towards the random and binary packings and sheds new light on the essence of the MDRP. Our work also guides the optimal particle size distributions of powders in chemical engineering process.

Towards fabrication of high-performance Al2O3 ceramics by indirect selective laser sintering based on particle packing optimization

Abstract A novel method to fabricate high-performance Al2O3 Ceramics by indirect Selective Laser Sintering (idSLS) based on particle packing optimization was reported. Al2O3 ceramics with the particle size distribution (PSD) being adjusted based on a particle packing model was prepared with the idSLS method, and the effects of PSD on the macro-performance and microstructure of the idSLSed ceramics part was investigated. Results show that an appropriate PSD of raw material is not only essential to the good SLS formability of powder bed but also contribute to the favorable sintering characteristics of the SLSed green body through an ideal particle packing. The improvement of overall properties including mechanic strength, dimensional accuracy, and surface flatness of the SLSed green body and the final parts were achieved with a fine-tuned PSD exponent. When the raw material has a PSD exponent of 0.5–0.6, the final ceramic parts showed relatively balanced comprehensive properties of bulk density >2.0 g cm−3, linear change 3.97 MPa, compressive strength >5.25 MPa and surface altitude difference

A Module Layout Method of Emergency Rescue Equipment Box Based on Layer Space

Module layout of emergency rescue equipment box is a special three-dimensional (3D) bin-packing problem, whose mathematical description is that under the condition of fixed capacity, the corresponding value of equipment in the box is maximized. Through the analysis of the characteristics of the emergency rescue equipment box, three evaluation indexes, including the average height of centroid, the average distance of access and the functional distance of equipment, were proposed first. In order to obtain a more ideal 3D packing scheme, a module layout method based on layer space using genetic algorithm was also proposed. These equipments to be arranged were encoded in decimal. According to the fitness function and the objective function, the selection, crossover and mutation operations of decimal sequence were conducted. After the iteration, the value of objective function gradually approached to the optimal solution. To evaluate the performance of the proposed method, some simulations under the MATLAB were performed. Finally, the experimental results show that the proposed method can achieve a better optimization effect, proving its effectiveness and feasibility.

The Use of Zeolites for VOCs Abatement by Combining Non-Thermal Plasma, Adsorption, and/or Catalysis: A Review

Non-thermal plasma technique can be easily integrated with catalysis and adsorption for environmental applications such as volatile organic compound (VOC) abatement to overcome the shortcomings of individual techniques. This review attempts to give an overview of the literature about the application of zeolite as adsorbent and catalyst in combination with non-thermal plasma for VOC abatement in flue gas. The superior surface properties of zeolites in combination with its excellent catalytic properties obtained by metal loading make it an ideal packing material for adsorption plasma catalytic removal of VOCs. This work highlights the use of zeolites for cyclic adsorption plasma catalysis in order to reduce the energy cost to decompose per VOC molecule and to regenerate zeolites via plasma.

Accurate In Silico Modeling of Asymmetric Bilayers Based on Biophysical Principles

Technological advances in the last decade have enabled the study of ever more complex and physiologically relevant model membranes to help dispel the mystery surrounding the role of plasma membrane asymmetry in various cellular processes. The slowly accumulating body of experimental data is fueling renewed interest in and the need for computational methods to support interpretations and address a wide range of problems that are still not amenable to direct experimental study. The specific appeal of molecular dynamics simulations for this purpose lies in their ability to access information at atomic resolution, which is useful for the formulation of testable mechanistic hypotheses. But, the range of questions that can be addressed reliably with such simulations is determined by the appropriate construction and simulation of asymmetric bilayer models. One essential way to achieve this goal is to follow rigorous biophysical criteria and principles. In this context, we show that the requirement for a robust comparison between the properties of simulated asymmetric and symmetric model membranes is for the tension in each bilayer leaflet to be zero. Commonly used methods for constructing asymmetric bilayers, including matching the average areas of the leaflets from the corresponding symmetric systems, do not ensure zero leaflet tension, thus precluding physically realistic changes in the areas of the two leaflets. We present, to our knowledge, a new method for identifying the ideal lipid packing in bilayers with different leaflet compositions that achieves the zero-tension goal, and discuss the basic principles underlying the biophysically correct computational study of asymmetric membranes.

Setting, rheology and packing density of biomass fly ash/Portland cement mixtures

Paper deals with rheological properties and packing density of fresh mixtures of Portland cement and biomass fly ash. Water demand of paste of normal consistency increases with increase of replacement level of biomass fly ash for Portland cement. Up to 5 wt. % contents of biomass fly ash yield stress and plastic viscosity values decrease, while at contents higher than 5 wt. %, the opposite trend was revealed. Biomass fly ash compared to Portland cement has proportionally lower content of particles with size of tens and first single digit numbers of microns. Deficiency in this region at higher contents of biomass fly ash in cement mixtures results in deflection from ideal packing density curve.

Clay, Water, and Salt: Controls on the Permeability of Fine-Grained Sedimentary Rocks.

The ability to predict the permeability of fine-grained soils, sediments, and sedimentary rocks is a fundamental challenge in the geosciences with potentially transformative implications in subsurface hydrology. In particular, fine-grained sedimentary rocks (shale, mudstone) constitute about two-thirds of the sedimentary rock mass and play important roles in three energy technologies: petroleum geology, geologic carbon sequestration, and radioactive waste management. The problem is a challenging one that requires understanding the properties of complex natural porous media on several length scales. One inherent length scale, referred to hereafter as the mesoscale, is associated with the assemblages of large grains of quartz, feldspar, and carbonates over distances of tens of micrometers. Its importance is highlighted by the existence of a threshold in the core scale mechanical properties and regional scale energy uses of shale formations at a clay content Xclay ≈ 1/3, as predicted by an ideal packing model where a fine-grained clay matrix fills the gaps between the larger grains. A second important length scale, referred to hereafter as the nanoscale, is associated with the aggregation and swelling of clay particles (in particular, smectite clay minerals) over distances of tens of nanometers. Mesoscale phenomena that influence permeability are primarily mechanical and include, for example, the ability of contacts between large grains to prevent the compaction of the clay matrix. Nanoscale phenomena that influence permeability tend to be chemomechanical in nature, because they involve strong impacts of aqueous chemistry on clay swelling. The second length scale remains much less well characterized than the first, because of the inherent challenges associated with the study of strongly coupled nanoscale phenomena. Advanced models of the nanoscale properties of fine-grained media rely predominantly on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, a mean field theory of colloidal interactions that accurately predicts clay swelling in a narrow range of conditions (low salinity, low compaction, Na+ counterion). An important feature of clay swelling that is not predicted by these models is the coexistence, in most conditions of aqueous chemistry and dry bulk density, of two types of pores between parallel smectite particles: mesopores with a pore width of >3 nm that are controlled by long-range interactions (the osmotic swelling regime) and nanopores with a pore width <1 nm that are controlled by short-range interactions (the crystalline swelling regime). Nanogeochemical characterization and simulation techniques, including coarse-grained and all-atom molecular dynamics simulations, hold significant promise for the development of advanced constitutive relations that predict this coexistence and its dependence on aqueous chemistry.

The damage mechanism of oil-based drilling fluid for tight sandstone gas reservoir and its optimization

The B block is a typical tight sandstone gas reservoir in Tarim basin in the Xinjiang Uygur Autonomous Region, China. In this block, the skin factors of each well drilled by oil-based drilling fluids were high and the reservoir damage was serious. The permeability recovery rates of two kinds of oil-based drilling fluids used in site were both less than 60%. To investigate the damage mechanism, the particle size distribution was tested to analyze solids damage incorporating the pore throat radius and micro-fracture width in this block. The contact angles of deionized water on reservoir cores before and after polluted by oil-based filtrate were measured to analyze the wettability alteration. Core flow experiment was applied to evaluate oil phase trapping, and the emulsion droplets formed by mixing oil-based filtrate with formation water were observed to analyze emulsion plugging damage. Based on the test results, the factors causing damage to the tight sandstone gas reservoir included solid phase invasion to fractures, wettability alteration, oil phase trapping and emulsion plugging.Therefore, the oil-based drilling fluids were optimized from aspects of reduction of the filtration loss, improvement of the sealing ability of the micro-fractures and reduction of the oil-water interfacial tension. A temporary plugging agent was compounded by using the Ideal Packing Theory, which could effectively plug the micro-fractures. The surfactant was optimized, and it could destroy the oil-based filtrate cake effectively and break emulsion in a short time. The permeability recovery rate of optimized oil-based drilling fluids was evaluated and the results showed that permeability recovery rate was 87.40% and 86.74%. Furthermore, cores early contaminated by oil-based drilling fluid were treated by optimized surfactant, and the tested permeability recovery rate reached more than 100%.

Extending thermal stability of calcium carbonate pills using sepiolite drilling fluid

Abstract The aim is to investigate the plugging ability of sepiolite clay water base drilling fluids over a wide range of high permeable zones at high temperature and high pressure conditions. The special emphasis of this study is to extend the usage of loss preventer material (LPM) as a component of fresh water sepiolite base mud that has never been investigated for this purpose before. The rheology and loss tests at 27−204 °C and 2070 or 6895 kPa revealed that the sepiolite drilling mud shows good rheology and high solid suspension capability at all temperatures except 149 °C, and low loss circulation at high temperature and high pressure. The Permeability Plugging Apparatus (PPA) experiment, in which the 10−90 µm permeable ceramic plate was simulated as formation, showed that the sepiolite drilling mud without CaCO 3 can not plug the pores, while the sepiolite drilling mud with CaCO 3 can plug the pores quickly and keep the CaCO 3 particles suspended even at high temperature (up to 193 °C). The PPA experiment results were proved by the analysis using SEM and ideal packing theory.

Porosity of bimodal sediment mixture with particle filling

The porosity of a bimodal sediment mixture is affected by the filling of fine particles in the voids of coarse particles when the particle size range is wide. The classical ideal packing models tend to overestimate the filling, and, thus, underestimate the porosity of the mixture. In this study, an existing random filling model is improved by considering a three-dimensional packing configuration, and a new model is developed by considering how many fine particles are required and how many are available to cover the surface of coarse particles in the sediment mixture. The developed models are validated using measured data and compared with existing models. The new model can reproduce well the variation trend of the mixture porosity as the fraction of fine particles varies.

The effect of boron powder on the microstructure of MgB2 filaments prepared by the modified internal magnesium diffusion technique

We have analyzed the microstructure of MgB2 prepared by the modified internal magnesium diffusion technique resulting in filaments without a central hole. Three different amorphous boron powders with a nominal purity of 98.5%–99.0% and a different particle size were used. It was shown that the real purity of the powders was different from the nominal purity, and the microstructure as well as the critical current densities of the MgB2 were affected by using boron. Larger B particles with a size of 400–500 nm led to the presence of large B-rich grains inside the MgB2 matrix. For one wire series, boron powder containing residual chlorine from the boron preparation process was used. It was found that just a small quantity of chlorine in the B powder caused significant MgB2 filament inhomogeneity, an apparent decrease in the critical current density and high reactivity with air. We estimated the ideal packing density for achieving a large volume of dense MgB2.

ДЕФОРМАЦИОННЫЕ СВОЙСТВА НАСЫПНОГО СЛОЯ ИЗ СВИНЦОВЫХ ШАРИКОВ

The results of a static investigation of the compression of granular layers from metal balls are presented. Metal balls are a promising damping element of the protective structures from explosive and impulse actions. With intensive actions, the granular layers deform irreversibly. Static compression of a filling medium was done at the Zwick Amsler HA 100 test machine. An experimental deformation diagram was obtained for uniaxial compression of a granulated layer of lead balls under static loading in a wide range of loading values up to the liquidation of free porosity. The diagram has a nonlinear and irreversible character. Loading of symmetric fragments of the layer has been numerically modeled for two versions of regular packing of the balls - tetrahedral and cubic. In both versions developed plastic flow of the material, filling the pores up to complete compaction, is observed. The numerical deformation diagrams, similar to the experimental ones, are strongly nonlinear and irreversible. The behavior of the experimental curve qualitatively corresponds to that of the numerical curves. This curve in the range between the deformation curve of the filling layer with tetrahedral and cubic ideal packing of the balls. Numerical modeling revealed that the zones of abrupt increase of resistance of the porous material are connected with liquidation of free porosity. Keywords: layer of balls, porous medium, experiment, static deformation, compression, nonlinearity, irreversibility, numerical modeling.

Optimum particle size distribution design for lost circulation control and wellbore strengthening

In this paper, we have experimentally studied the impact of particle size distribution (PSD) on the fracture sealing capability of lost circulation material (LCM) blends. Our primary aim was to determine the PSD which maximizes the Wellbore Strengthening (WBS) benefits obtained from fracture sealing. High-pressure borehole fracturing experiments were conducted on Berea sandstone samples under atmospheric pore pressure and various confining pressures to investigate the WBS effects of several LCM blends. Post-fracturing methods such as Computerized Axial Tomography (CAT) scan and thin-section imaging were used to investigate the geometry of induced fractures and formed seals within them. Based on the conducted experiments and post-fracturing analyses, we have evaluated and re-assessed well-known theories applicable to the design of LCM blends, such as the one-third rule, the ideal packing theory, and the Vickers criteria. Our experiments indicate that for any rock with a given set of rock strength and failure parameters, there exists an optimum PSD to maximize WBS benefits. Optimum PSD appears to be of primary importance, almost independent of LCM type. In addition, we have shown that the optimum PSD should have a bimodal structure, with sufficient concentrations of properly sized fine and coarse particles. Although the one-third rule, the ideal packing theory, and the Vickers criteria may provide some basic PSD guidelines, these theories are mainly empirical relationships based on conventional particle plugging experiments. As shown here, they do not properly represent the physics of fracture sealing. To remedy this situation, we are introducing a new family of design curves for optimum PSD, based on the underlying physics of fracture sealing observed in the WBS experiments.

Critical slowing down and hyperuniformity on approach to jamming.

Hyperuniformity characterizes a state of matter that is poised at a critical point at which density or volume-fraction fluctuations are anomalously suppressed at infinite wavelengths. Recently, much attention has been given to the link between strict jamming (mechanical rigidity) and (effective or exact) hyperuniformity in frictionless hard-particle packings. However, in doing so, one must necessarily study very large packings in order to access the long-ranged behavior and to ensure that the packings are truly jammed. We modify the rigorous linear programming method of Donev etal. [J. Comput. Phys. 197, 139 (2004)JCTPAH0021-999110.1016/j.jcp.2003.11.022] in order to test for jamming in putatively collectively and strictly jammed packings of hard disks in two dimensions. We show that this rigorous jamming test is superior to standard ways to ascertain jamming, including the so-called "pressure-leak" test. We find that various standard packing protocols struggle to reliably create packings that are jammed for even modest system sizes of N≈10^{3} bidisperse disks in two dimensions; importantly, these packings have a high reduced pressure that persists over extended amounts of time, meaning that they appear to be jammed by conventional tests, though rigorous jamming tests reveal that they are not. We present evidence that suggests that deviations from hyperuniformity in putative maximally random jammed (MRJ) packings can in part be explained by a shortcoming of the numerical protocols to generate exactly jammed configurations as a result of a type of "critical slowing down" as the packing's collective rearrangements in configuration space become locally confined by high-dimensional "bottlenecks" from which escape is a rare event. Additionally, various protocols are able to produce packings exhibiting hyperuniformity to different extents, but this is because certain protocols are better able to approach exactly jammed configurations. Nonetheless, while one should not generally expect exact hyperuniformity for disordered packings with rattlers, we find that when jamming is ensured, our packings are very nearly hyperuniform, and deviations from hyperuniformity correlate with an inability to ensure jamming, suggesting that strict jamming and hyperuniformity are indeed linked. This raises the possibility that the ideal MRJ packings have no rattlers. Our work provides the impetus for the development of packing algorithms that produce large disordered strictly jammed packings that are rattler free, which is an outstanding, challenging task.

Wastewater-nitrogen removal using polylactic acid/starch as carbon source: Optimization of operating parameters using response surface methodology

Nitrogen removal from ammonium-containing wastewater was conducted using polylactic acid (PLA)/starch blends as carbon source and carrier for functional bacteria. The exclusive and interactive influences of operating parameters (i.e., temperature, pH, stirring rate, and PLA-to-starch ratio (PLA proportion)) on nitrification (Y 1), denitrification (Y 2), and COD release rates (Y 3) were investigated through response surface methodology. Experimental results indicated that nitrogen removal could be successfully achieved in the PLA/starch blends through simultaneous nitrification and denitrification. The carbon release rate of the blends was controllable. The sensitivity of Y 1, Y 2, and Y 3 to different operating parameters also differed. The sequence for each response was as follows: for Y 1, pH>stirring rate>PLA proportion>temperature; for Y 2, pH>PLA proportion>temperature> stirring rate; and for Y 3, stirring rate>pH>PLA proportion>temperature. In this study, the following optimum conditions were observed: temperature, 32.0°C; pH 7.7; stirring rate, 200.0 r ∙min–1; and PLA proportion, 0.4. Under these conditions, Y 1, Y 2, and Y 3 were 134.0 μg-N∙gblend–1∙h–1, 160.9 μg-N∙g-blend–1∙h–1, and 7.6 × 103 μg-O∙g-blend–1∙h–1, respectively. These results suggested that the PLA/starch blends may be an ideal packing material for nitrogen removal.

Side chain effects in the packing structure and stiffness of redox-responsive ferrocene-containing polymer brushes

This paper describes the preparation of ferrocene-containing polymer brushes with different side chain lengths by surface-initiated atom transfer radical polymerization (SI-ATRP). The polymer brushes are characterized by cyclic voltammetry to determine the surface coverage of the ferrocene (Fc) units, their thickness in air by atomic force microscopy (AFM) and ellipsometry, and their mechanical properties by AFM-based nanoindentation. The results are compared against an ideal packing model and we conclude that brushes with short linkers between the Fc units and the polymer back bone are stiff and stand up in air up to 40nm tall. In contrast, polymers with long linkers collapse and do not stand up in air. Our results indicate that the stiffness and packing structure of Fc-containing polymer brushes are affected by the length of the linkers between the Fc and polymer back bone.

The crystal chemistry of inorganic metal borohydrides and their relation to metal oxides

The crystal structures of inorganic homoleptic metal borohydrides are analysed with respect to their structural prototypes found amongst metal oxides in the inorganic databases such as Pearson's Crystal Data [Villars & Cenzual (2015). Pearson's Crystal Data. Crystal Structure Database for Inorganic Compounds, Release 2014/2015, ASM International, Materials Park, Ohio, USA]. The coordination polyhedra around the cations and the borohydride anion are determined, and constitute the basis of the structural systematics underlying metal borohydride chemistry in various frameworks and variants of ionic packing, including complex anions and the packing of neutral molecules in the crystal. Underlying nets are determined by topology analysis using the program TOPOS [Blatov (2006). IUCr CompComm. Newsl. 7, 4-38]. It is found that the Pauling rules for ionic crystals apply to all non-molecular borohydride crystal structures, and that the latter can often be derived by simple deformation of the close-packed anionic lattices c.c.p. and h.c.p., by partially removing anions and filling tetrahedral or octahedral sites. The deviation from an ideal close packing is facilitated in metal borohydrides with respect to the oxide due to geometrical and electronic considerations of the BH4(-) anion (tetrahedral shape, polarizability). This review on crystal chemistry of borohydrides and their similarity to oxides is a contribution which should serve materials engineers as a roadmap to design new materials, synthetic chemists in their search for promising compounds to be prepared, and materials scientists in understanding the properties of novel materials.