Bimodal Suspensions Research Articles

Bimodal suspensions: semi-empirical prediction of viscosity and linear viscoelastic response

Bimodal suspensions: semi-empirical prediction of viscosity and linear viscoelastic response

Enhanced Flowability and Slurry Characteristics of Limestone-water Suspensions Through the Integration of Coarse Particles and a Natural Additive

Mineral slurry preparation and pipeline transport require careful particle size distribution and additive selection to ensure cost-effective and reliable transportation. The research described here was aimed to better understand the flow behavior of a limestone sample by combining coarse and fine particles and a low-cost natural additive, Saponin, derived from Sapindus laurifolia. Four distinct bi-modal suspension samples were formed using various mixtures of limestone samples with sizes varying from 0–53 and 75–106 µm. The rheological characteristics of the suspension were investigated at shear rates of 50 to 500 s−1 for solid concentrations 40–70% by weight. The additive’s critical micelle concentration was found to be 1.8 weight percent. The Hershel-Bulkley model fits the experimental data the best. The appropriate proportion of coarse particles was discovered to be 30% based on critical factors such as apparent viscosity and pressure drop. The addition of the surfactant reduced the surface tension, increased the wettability, and decreased the particle-particle interaction to stabilize the limestone-water suspension.

Investigation of the Physicochemical Interactions and Modification Effects of Polyurethane on Asphalt Binder

Polyurethane (PU) is a synthetic polymeric material with excellent mechanical properties and chemical designability. An in-depth understanding of the synergetic effect between polyurethane and asphalt binder is needed to produce durable PU-modified asphalt paving materials. This study focuses on the physicochemical changes, the states of in situ synthesized PU, and the modification effects of PU after PU prepolymers and chain extenders are added into asphalt binder. Investigation methods involve the Fourier transform infrared (FTIR) spectroscopy, partial Corbett separation, confocal fluorescence microscopy, particle size distribution test, rheological test, and theoretical calculation. It was found that the incorporation of PU has no obvious chemical influence on the asphalt binder and the main working principle of PU modification is its physical dispersion in asphalt binder. In situ synthesized PU is uniformly dispersed in asphalt binder and the size distribution of PU particles follows a log-normal distribution. As PU content exceeds 15%, the formed PU particles in asphalt binder are noticeably enlarged. Moreover, PU modification leads to significant improvements in asphalt binder properties, including high-temperature rutting resistance, elastic recovery, and deformation resistance. Rheological experiments and theoretical calculations under the framework of suspension rheology indicate that PU-modified asphalt binder can be reasonably modeled as a bimodal solid particle suspension, and the dynamic viscosity of PU-modified asphalt binder is predominantly determined by the dynamic viscosity of the maltenes and the volume fractions of PU and asphaltenes.

Homogeneity verification of samples produced via Sandwich freeze-drying

Sandwich freeze-drying can provide dispersions of nanoparticles on a substrate with little aggregation, which is convenient for microscope imaging. We examined suspensions of spherical silica nanoparticles deposited on silicon substrates via sandwich freeze-drying. The substrates were imaged through atomic force microscopy (AFM) and the particle size distributions were computed. We corrected the distributions in light of the grid-based discrete nature of AFM. This preparation and measurement-computation scheme enabled us to analyze wide-ranging size distributions. For monomodal distributions with nominal diameters of 50nm and 100nm, the z-average diameters coincided with dynamic light scattering results with an accuracy of 1nm. Two monomodal suspensions were mixed to form a bimodal suspension and the size distribution was deduced. Despite the wide size distribution, we obtained a result consistent with the monomodal data. Furthermore, we observed Ostwald ripening in the bimodal suspension via successive measurements over five years. To check to see if the method produced a good representation of the nanoparticles, we performed a high-level analysis by deducing the actual size distribution of spherical nanoparticles from AFM data.

Sizing multimodal suspensions with differential dynamic microscopy.

Differential dynamic microscopy (DDM) can be used to extract the mean particle size from videos of suspensions. However, many suspensions have multimodal particle size distributions, for which a single 'mean' is not a sufficient description. After clarifying how different particle sizes contribute to the signal in DDM, we show that standard DDM analysis can extract the mean sizes of two populations in a bimodal suspension given prior knowledge of the sample's bimodality. Further, the use of the CONTIN algorithm obviates the need for such prior knowledge. Finally, we show that by selectively analysing portions of the DDM images, we can size a trimodal suspension where the large particles would otherwise dominate the signal, again without prior knowledge of the trimodality.

Fabrication of X-ray absorption gratings by centrifugal deposition of bimodal tungsten particles in high aspect ratio silicon templates

Grating-based X-ray imaging employs high aspect ratio absorption gratings to generate contrast induced by attenuating, phase-shifting, and small-angle scattering properties of the imaged object. The fabrication of the absorption gratings remains a crucial challenge of the method on its pathway to clinical applications. We explore a simple and fast centrifugal tungsten particle deposition process into silicon-etched grating templates, which has decisive advantages over conventional methods. For that, we use a bimodal tungsten particle suspension which is introduced into a custom designed grating holder and centrifuged at over 1000×g. Gratings with 45 µm period, 450 µm depth, and 170 mm × 38 mm active area are successfully processed reaching a homogeneous absorber filling. The effective absorbing tungsten thickness in the trenches is 207 µm resulting in a filling ratio of 46.6% compared to a voidless filling. The grating was tested in a Talbot–Lau interferometer designed for clinical X-ray dark-field computed tomography, where visibilities up to 33.6% at 60 kV were achieved.

Nonlinear Agglomeration of Bimodal Colloids under Microgravity

Abstract A study of like-charged, bimodal colloidal suspensions was conducted in microgravity aboard the International Space Station as part of NASA's Advanced Colloids Experiments-Heated-2 (ACE-H-2) experiments. Samples comprised of silsesquioxane microparticles (600 nm) and zirconia nanoparticles (5–15 nm) in 1.5 pH nitric acid were mixed and allowed to agglomerate over time while being imaged with NASA's Light Microscopy Module (LMM). The samples contained 1% of microparticles with varying concentrations of nanoparticles in 0.1%, 0.055%, and 0.01% by volume. Digital images were captured periodically by the LMM over 12 days. Image analysis, including cluster size and distribution, was performed in Python using the “Colloidspy” package. The study found that cluster size had increased over time in at least seven of nine samples, but two samples exhibited nonlinear growth rates, while others showed very slow growth with cluster sizes two orders of magnitude greater than the free microparticles. We hypothesize that all samples experienced nonlinear growth, but early transient effects after mixing were missed due to timing limitations in image acquisition. Transport limitations of clusters in these systems may have dominated agglomeration behavior in microgravity, despite the samples being thermodynamically unstable, but more study is required.

Determination of the Size Distribution of Metallic Colloids from Extinction Spectroscopy.

In this paper, we explore the ability of extinction spectroscopy to characterize colloidal suspensions of gold nanoparticles (Au NPs). We demonstrate that the Au NPs’ size distribution can be deduced by analyzing their extinction spectra using Mie theory. Our procedure, based on the non-negative least square algorithm, takes advantage of the high sensitivity of the plasmon band to the Au NP size. In addition, this procedure does not require any a priori information on the Au NP size distribution. The Au NPs’ size distribution of monomodal or bimodal suspensions can be satisfactorily determined from their extinction spectra. Finally, we show that this characterization tool is compatible with in situ measurement and allows following the change in NPs’ radii during laser exposure.

Rheology of Highly Concentrated Suspensions with a Bimodal Size Distribution of Solid Particles for Powder Injection Molding.

Powder injection molding (PIM) is one of the modern and prospective technologies in processing different materials. We proposed to use bimodal compositions of particles for increasing their content in the final products. A set of model suspension of Al with low-molecular-weight poly (ethylene glycol) as a binder based on theoretical arguments concerning the filling capacity of bimodal suspensions was prepared. Studying the rheological properties of these compositions showed that they demonstrate elasto-viscous behavior with significant plasticity that is favorable for the technological process. Using compositions with bimodal distributions allows for increasing the content of the solid phase up to 75 vol. % for PIM technology, which is significantly higher than the standard practical limit. This rheological approach developed for model formulations was applied to processing compositions containing aluminum oxide as typical ceramics and polyolefines as a binder widely used in technological practice. The obtained sintered ceramic samples have quite acceptable mechanical properties of the usual corundum articles.

Viscosity investigation on metastable hydrate suspension in oil-dominated systems

Predicting the viscosity of hydrate slurries is essential in evaluating the transport performance of oil and gas in deep-water pipelines and the risk of blockage. In this work, based on the Camargo–Palermo model and the bimodal suspension model, a new viscosity model was developed for hydrate slurries. In this model, the viscosity of slurry is determined jointly by small hydrate particles and larger hydrate aggregates, in which the maximum critical diameter of the aggregate is controlled by shear force and cohesion force, while amount of hydrate particles and aggregates can be described by a dimensionless parameter proposed. In addition, rheological measurements of methane hydrate slurry formed from water-in-oil emulsion were conducted with a high-pressure rheometer to validate the developed model. The predictions of the model agree well with the experimental data for metastable hydrate suspension in oil-dominated systems with either different initial water cuts or different water conversion rates.

Fabrication of BSCF-based mixed oxide ionic-electronic conducting multi-layered membrane by sequential electrophoretic deposition process

The Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF)-based multi-layered oxygen separation membrane was fabricated by the sequential electrophoretic deposition (EPD) process. A thin porous/dense bi-layer of BSCF was formed on a thick porous support of BSCF. The porous support prepared by a sacrificial template method using BSCF powder mixed with wheat starch (30 wt%) as a pore-forming agent, followed by uniaxial pressing and low-temperature sintering, was directly used as an EPD electrode. A thin BSCF layer was first formed on the porous support, and then a thin BSCF + PMMA (polymethyl methacrylate) layer was sequentially formed on the thin BSCF layer using a bimodal suspension of BSCF and PMMA. A 30-μm thin porous/dense bi-layer of BSCF of which the total thickness was obtained by optimizing the processes of EPD and subsequent co-sintering. The oxygen separation performance of 3.7 ml (STP) min−1 cm−2 at 860 °C was achieved for the BSCF-based multi-layered oxygen separation membrane.

Shear viscosity of bimodal capsule suspensions in simple shear flow

A well-known rheological property of a suspension of two sizes of rigid particles is a reduction in the shear viscosity. A numerical analysis shows that for bimodal capsule suspensions, the extent of the viscosity reduction is amplified by the deformability of the capsules.

Stimuli-Responsive DNA-Linked Nanoparticle Arrays as Programmable Surfaces

Self- and directed-assembly approaches have enabled precise control over the composition and geometry of 2D and 3D nanoparticle constructs. However, the resulting structures are typically static, providing only a single structural arrangement of the nanoparticle building blocks. In this work, the power of DNA-linked nanoparticle assembly is coupled to a grayscale patterning technique to create programmable surfaces for assembly and thermally activated reorganization of gold nanoparticle arrays. Direct grayscale patterning of DNA monolayers by electron-beam lithography (DNA-EBL) enables the production of surfaces with nanometer-scale control over the density of functional DNA. This enables tuning of the particle-surface interactions with single-nanoparticle resolution and without the need for a physical template as employed in most directed assembly methods. This technique is applied on suspended membrane structures to achieve high-resolution assembly of 2D nanoparticle arrays with highly mutable architectures. Gold nanorods assembled on grayscale-patterned surfaces exhibit temperature-dependent configurations and ordering behavior that result in tunable polarization-dependent optical properties. In addition, spherical gold particles assembled from a bimodal suspension produce arrays with temperature-dependent configurations of small and large particles. These results have important implications for the design and fabrication of reconfigurable nanoparticle arrays for application as structurally tunable optical metasurfaces.

Rheological Characteristics of Uni/Bi-Variant Particulate Iron Ore Slurry: Artificial Neural Network Approach

A rigorous literature review has been carried out on rheological behavior of hard and soft particle slurries. The rheological characteristics of unimodal and bimodal suspension are presented. From experimentation, it was observed that mineral viscosity increases with solid concentration, while decreases with temperature. Addition of 30% (by weight) proportion of finer particles in coarse particles resulted in significant decrease in apparent viscosity of iron ore suspension. Artificial neural network approach was used for predicting the apparent viscosity of slurry.

Depletion-induced interaction in concentrated bimodal suspensions of nanosilica in poly(ethylene glycol)

In this work, we examine the effect of short-range depletion attraction on the rheology of concentrated bimodal suspensions. The depletion interaction is driven by small particle exclusion from the space between big particles with a magnitude depending on the relative concentration of the constituents. We have chosen two particle size ratios, δ = 3.4 and 6.8, in constant volume fraction ϕ = 0.59 to study the depletion-induced bonding between large particles in the poly(ethylene glycol)/nanosilica suspensions without liquid-liquid phase separation. The clustering of large particles in the samples is characterized via the thixotropic behavior and shear thickening response. Bimodal suspensions with R = 0.6 and 0.75 at δ = 6.8 show thixotropy and reduced zero-shear viscosity compared to bimodal samples with the same R at δ = 3.4 size ratio. Additionally, the onset of shear thickening obtained from the experimental and both modeling results occurs at significantly lower shear rates in samples, which contain more clusters of large particles. Finally, we propose a modified state diagram for bimodal concentrated suspensions based on the rheological measurements.

Pore space colmatation during the bimodal suspension flow through the porous medium

Pore space colmatation during the bimodal suspension flow through the porous medium

Enhancing magnetorheological effect using bimodal suspensions in the single-multidomain limit

We demonstrate a new route to enhance the magnetorheological effect using bimodal suspensions in the single-multidomain limit. Experimental results are satisfactorily compared to 3D finite element method simulations. The physical reason behind this enhancement is the coating of the larger particles by the smaller ones due to the remnant magnetization of the latter.

Effects of the evaporation rate on the segregation in drying bimodal colloidal suspensions

When suspensions containing colloidal particles of two different sizes are coated on substrates to form films by evaporating the host fluids, the smaller particles can segregate to the top surface of the films. We investigate the effects of the evaporation rate on the segregation by use of Langevin dynamics simulations. The evaporation rate is scaled by the Brownian diffusion rate of the particles, yielding a dimensionless number which we define as the particle drying Péclet number. We show that there is a Péclet number at which the segregation is the most enhanced. Our result indicates the need for the regulation of the evaporation rate to control the segregation.

Effect of affinity on the structure formation in highly size asymmetric bimodal suspensions

We investigate the influence of inter-particle affinity on the microstructure and rheological behavior in the bimodal suspension systems. For this purpose, we design the suspensions using two kinds of polystyrene beads (PS, size ∼530nm) as a large particle which are electrostatically stabilized and are different in surface properties only, while keeping unstable alumina coated silica (Al-silica, size ∼12nm) as a small particle. To change the affinity, hydrogen bonding is induced by modifying surface of PS as poly (vinyl pyrrolidone) (PVP). The influence of affinity between large and small particles is investigated by observing the changes in rheological properties and microstructure. Even with the same, the formation of Al-silica cluster which connects large particles is dominant when sulfate modified PS is used and the affinity between the particles is not strong. On the contrary, the Al-silica particles cover the surface of large particles rather than making bridges when PVP modified PS is used and the affinity is strong. The phase map which shows fluid-gel transition according to the composition of the suspension is also obtained. The affinity is found to affect the shape of the phase map too. This research explains how the differences in affinity between large and small particles affect the bimodal suspensions according to the surface properties of the particles, and provides an insight on the complex behavior of particulate fluids.

An experimental study of multimodal glass suspension rheology to test and validate a polydisperse suspension viscosity model

Experimental measurements of non-colloidal multimodal suspension viscosities are performed over a wide range of mixing ratios and used to test the robustness and predictive capability of a recent viscosity model (Mwasame et al. in Phys Fluids 28:061701, 2016b), subsequently referred to as the MWB model. Three unimodally distributed particle suspensions with narrow size distributions are blended to make the bimodal and trimodal suspensions used in the rheological experiments. We demonstrate how predictions for mixture viscosities can be made using the MWB model only requiring the volume-weighted average particle sizes and viscosity correlations of the individual unimodal suspensions comprising the blend. The resultant model predictions are found to be in good agreement with measured bimodal and trimodal viscosity data to within expected experimental uncertainty. The datasets provided here can be used to validate future modeling efforts, and the MWB model can be used to optimize the viscosity of multimodal suspension mixtures for specific performance criteria.