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Linear response theory relates the decay of equilibrium magnetisation fluctuations in a ferrofluid to the frequency-dependent response of the magnetisation to a weak ac external magnetic field. The characteristic relaxation times are strongly affected by interactions between the constituent particles. Similarly, the relaxation of an initially magnetised system towards equilibrium in zero field occurs on a range of timescales depending on the structure of the initial state, and the interactions between the particles. In this work, ferrofluids are modelled as colloidal suspensions of spherical particles carrying point dipole moments, and undergoing Brownian motion. Recent theoretical and simulation work on the relaxation and linear response of these model ferrofluids is reviewed, and the effects of interactions, structure formation, and polydispersity on the characteristic time scales are outlined. It is shown that: (i) in monodisperse ferrofluids, the timescale characterising the collective response to weak fields increases with increasing interaction strength and/or concentration; (ii) in monodisperse ferrofluids, the initial, short-time decay is independent of interaction strength, but the asymptotic relaxation time is the same as that characterising the collective response to weak fields; (iii) in the strong-interaction regime, the formation of self-assembled chains and rings introduces additional timescales that vary by orders of magnitude; and (iv) in polydisperse ferrofluids, the instantaneous magnetic relaxation time of each fraction varies in a complex way due to the role of interactions. © 2022 The Authors

In this study, the gelation behavior of TEMPO-oxidized wood-based cellulose nanofiber (CNF) suspensions in two different glycols, ethylene glycol (EG) and propylene glycol (PG), was investigated near the overlap concentration and compared with that of aqueous CNF suspensions. The flow property of these non-aqueous and aqueous CNF suspensions was characterized by rheological, UV-vis, and rheo-optical techniques. It was found that the CNF(PG) suspensions exhibited stirring-reversible gelation behavior, where gelation could be induced simply by resting (i.e., prolonged holding time). However, this behavior was not observed for CNF(EG) and CNF(aq) suspensions. Higher temperature and higher CNF concentration could accelerate the gelation process of CNFs in PG, but no large-scale phase separation was detected by the optical techniques. Our study suggests that the reduced hydrophilic attraction between CNFs in PG is the main driving force for forming CNF-rich micro-domains, yielding a physically crosslinked network. This study suggests that the choice of solvent can be used to tailor and control the flow behavior of CNF suspensions, leading to designs of new cellulose-enabled nanocomposites for varying applications., QC 20230613

The term "active matter"describes a class of out-of-equilibrium systems, whose ability to transform environmental to kinetic energy is sought after in multiple fields of science. A challenge that still remains is to craft nanometer-sized active particles, whose motion can be efficiently directed by externally applied bio-noninvasive stimuli. Adding a magnetic component and therefore being able to direct the motion of active nanoparticles with an applied magnetic field is one of the promising solutions in the field. In this study, we employ molecular dynamics simulations to predict an external field-induced flow that arises in mixtures of magneto-active nanosized cubic and spherical particles with distinct mutual orientations between magnetization and propulsion. We explain why the flux of the suspended particles in the field direction does not only depend on the angle between the active force, driving a particle forward, and the orientation of its magnetization, but also on particle shape and inter-particle interactions. Our results show that by tuning those parameters, one can achieve complete separation of particles according to their magnetization orientation. Based on our findings, along with optimizing the cargo properties of magneto-active nano-units, the actual composition of the magneto-active particle suspension can be characterized. © the Owner Societies.

When concentrated particle suspensions flow into a constricting channel, the suspended particles may either smoothly flow through the constriction or jam and clog the channel. These clogging events are typically detrimental to technological processes, such as in the printing of dense pastes or in filtration, but can also be exploited in micro-separation applications. Many studies have to date focused on important parameters influencing the occurrence of clogs, such as flow velocity, particle concentration, and channel geometry. However, the investigation of the role played by the particle surface properties has surprisingly received little attention so far. Here, we study the effect of surface roughness on the clogging of suspensions of silica particles under pressure-driven flows along a microchannel presenting a constriction. We synthesize micron-sized particles with uniform surface chemistry and tunable roughness and determine the occurrence of clogging events as a function of velocity and volume fraction for a given surface topography. Our results show that there is a clear correlation between surface roughness and flow rate, indicating that rougher particles are more likely to jam at the constriction for slower flows. These findings identify surface roughness as an essential parameter to consider in the formulation of particulate suspensions for applications where clogging plays an important role., QC 20220427

This study investigates the influence of the ionic strength on the dead-end filtration of microcrystalline cellulose (MCC) suspensions in the range of 0.1–1 g/L NaCl, in altering the electrostatic interactions between particles. The formation of larger agglomerates of increasing ionic concentration was observed using Focused Beam Reflectance Measurement (FBRM®). Local filtration properties were investigated as the experimental set-up allowed for measurements of local hydrostatic pressure and solidosity to be made. The results show that the addition of ions decreases both the average and local filtration resistance. The formation of a resistant skin layer was observed for the suspension without the addition of NaCl but was counteracted when ions were added. Furthermore, the ionic strength did not seem to have any notable effect on the structure of the cake in the range 0.15–1.0 g/L NaCl. However, the pressure dependency of the solidosity at lower ionic concentration was higher. The local filtration properties were fitted to semi-empirical relations, which indicated the formation of moderately to highly compressible cakes when NaCl was added., QC 20211123

Nanocellulosic coatings as a food-packaging material are of commercial interest due to their non-toxic nature, renewability, and excellent barrier properties. Complex shear-thinning rheology poses challenges in designing and sizing equipment to pump, mix, and process the suspension and actual coating process. This study aims to determine the effectiveness of computation fluid dynamics (CFD) in predicting nanocellulosic suspension flow in light of existing rheological data. We employ and compare three distinct rheological models to characterize the rheology and flow of nanocellulose suspensions through a slot-die coater, where the model parameters are established from existing slot-rheometry measurements. A volume-of-fluid (VoF) based finite volume method is employed to simulate the flow in a slot-die operated in an unconventional metering mode. Results with the Casson model predicts the presence of unyielded regions in the flow, which was not captured using the power-law model. These stagnation regions will incur coatability issues stemming from flow intermittencies and lead to potential defects in the coating layer, including fracture. The results suggest that a rheological model that includes yield stress should be considered while modeling such flows. A need for better rheological data to model nanocellulosic flows, especially at high consistencies and shear-rates, is also highlighted., Part of proceedings: ISBN 978-1-7138-4837-0QC 20220927

Interaction of conjugated polymers with liposomes is an attractive approach that benefits from both systems’ characteristics such as electroactivity and enhanced interaction with cells. Conjugated polymer-liposome complexes have been investigated for bioimaging, drug delivery, and photothermal therapy. Their fabrication has largely been achieved by multistep procedures that require first the synthesis and processing of the conjugated polymer. Here, a new one step fabrication approach is reported based on in situ polymerization of a conjugated monomer precursor around liposomes. Polyaniline (PANI) doped with phytic acid is synthesized via oxidative polymerization in the presence of 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) vesicles to produce a conductive aqueous suspension of Liposome-PANI complexes. PANI interacts with liposomes without disrupting the bilayer as shown using differential scanning calorimetry and fluorescence quenching studies of the hydrophobic Nile red probe. The electronic conductivity of the Liposome-PANI complexes, which stems from the doped PANI accessible on the liposome surface, is confirmed using conductive atomic force microscopy and electrochemical impedance spectroscopy. Further, short-term in vitro cell studies show that the complexes colocalize with the cell membrane without reducing cell proliferation. This study presents a novel fabrication route to conductive suspensions of conjugated polymer-liposome complexes suitable for potential applications at the biointerface., QC 20201203

The α-chitin nanofibril is an alternative to nanocellulose as a building-block for strong films and other nanomaterials. The hypothesis of high film strength for films based on mildly treated insect cuticles was tested. Fibrils from the cuticle of Ruspolia differens (a long-horned bush cricket grasshopper locally known as senene) are disintegrated by a mild process, subsequently characterized by transmission electron microscopy, NMR, Fourier transform infrared spectroscopy, and XRD, and used to prepare strong and transparent films. A mild process (with 20% NaOH treatment for 2 weeks and at room temperature) was used to largely remove the strongly bound protein associated with chitin. The purpose was to reduce chitin degradation. The native structure of chitin was indeed well preserved and close to the native state, as is supported by data for degree of acetylation, molar mass, crystallinity, and crystallite dimensions. The diameter of the smallest chitin fibrils was as small as 3-7 nm (average 6 nm) with lengths larger than or around 1 μm. A stable and well-dispersed colloidal chitin fibril suspension in water was achieved. A nanostructured chitin film prepared by filtration showed high optical transmittance (∼90%) and very high tensile strength (220 MPa). The high tensile strength was attributed to the well-preserved chitin structure, high intrinsic fibril strength, and high colloidal stability of the fibril suspension. Strong, transparent insect chitin films offer interesting alternatives to nanocellulose films because of different resource origins, surface chemistries, and potential antimicrobial properties., QC 20200409

Industrial production of low-charge microfibrillated cellulose (MFC) typically results in wide fibril size distributions. This polydispersity influences viscosity, overall colloidal stability, and rheological properties of MFC suspensions and gels in aqueous systems. In this work, a systematic rheological analysis is performed for industrially prepared MFC and fractions of different size distributions. Gel formation and flow characteristics (e.g., shear-thinning) of each fraction are examined under neutral and acidic conditions and compared with the unfractionated MFC suspension. The effects of size, aspect ratio, and surface charge on the rheology of semi-dilute MFC suspensions are discussed. The results demonstrate that particle size and aspect ratio distribution control the viscoelasticity and shear-thinning properties of MFC suspensions. An increased fraction of small diameter nanofibrils, by ex situ addition of the fine particles with high aspect ratio or removal of the coarsest particles (with lower aspect ratio) by fractionation, significantly enhances the storage modulus and the yield stress of the complex mixture, compared to the properties of the coarser fractions. New insights are also reported on the tailoring of the rheology of highly polydisperse fibrillar mixtures, where the rheological contributions of each fraction are discussed. Graphic abstract: [Figure not available: see fulltext.]. © 2020, The Author(s)., QC 20201201

Nanoscale solid particles suspended in a base liquid are a new class of nano-engineered colloidal suspension, defined with a coined name of nanofluids (NFs). The effect of dispersing nanoparticles (NPs) on the hydraulic and thermal (hydrothermal) performance of the conventional coolants is a matter of importance in many applications. This work experimentally and numerically presents the effect of different parameters, including the concentration and size of the NPs, on two primary parameters, namely heat transfer coefficient and friction factor in a microtube. The numerical modeling of colloidal suspensions was conducted based on single-phase as well as Eulerian-Mixture two-phase approaches and showed a good agreement with experimental results. The numerical results displayed that the suspended NPs remarkably increased the convective heat transfer coefficient as well as friction factor by as much as 42% and 22% (in NP concentration range of 1%–9%, and NP size range of 13–130 nm and Reynolds number of 400) respectively. Besides, two new correlations were developed based on the results obtained from experimentally validated models to predict the hydrothermal response of NFs in the laminar regime. Moreover, correlations were successfully created to predict the Nusselt number and friction factor of nanofluids, with ±8% and ±5% agreement between numerical data and predictions, respectively., QC 20200329

We consider suspensions of rigid bodies in a two-dimensional viscous fluid. Even with high-fidelity numerical methods, unphysical contact between particles occurs because of spatial and temporal discretization errors. We extend a time stepping method that avoids overlap by imposing a minimum separation distance between all pairs of bodies. In its original form, the method discretizes interactions between different particles explicitly. Therefore, to avoid stiffness, a large minimum separation distance is used. In this paper, we introduce a new implicit time stepping method that is able to simulate dense suspensions with large time step sizes and a small minimum separation distance. The method is tested on various unbounded and bounded flows, and rheological properties of the resulting suspensions are computed., QC 20200401

Magnetic nanogels represent a cutting edge of magnetic soft matter research due to their numerous potential applications. Here, using Langevin dynamics simulations, we analyse the influence of magnetic nanogel concentration and embedded magnetic particle interactions on the self-assembly of magnetic nanogels at zero field. For this, we calculated radial distribution functions and structure factors for nanogels and magnetic particles within them. We found that, in comparison to suspensions of free magnetic nanoparticles, where the self-assembly is already observed if the interparticle interaction strength exceeds the thermal fluctuations by approximately a factor of three, self-assembly of magnetic nanogels only takes place by increasing such ratio above six. This magnetic nanogel self-assembly is realised by means of favourable close contacts between magnetic nanoparticles from different nanogels. It turns out that for high values of interparticle interactions, corresponding to the formation of internal rings in isolated nanogels, in their suspensions larger magnetic particle clusters with lower elastic penalty can be formed by involving different nanogels. Finally, we show that when the self-assembly of these nanogels takes place, it has a drastic effect on the structural properties even if the volume fraction of magnetic nanoparticles is low. © 2019 Elsevier B.V.

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. © 2020

The motion of flocculated fibres in a streaming suspension is governed by the balance of the network strength and hydrodynamic forces. With increasing flow rate through a channel, (1) the network initially occupying all space, (2) is then compressed to the centre, and (3) ultimately dispersed. This classical view neglects fibres-fines: we find that the distribution of these small particles differs in streaming suspensions. While it is known that fibre-fines can escape the fibre network, we find that the distribution of fibre-fines is non-homogenous in the network during compression: fibre-fines can be caged and retarded in the streaming fibre network. Hence, the amount of fibre-fines is reduced outside of a fibre network and enriched at the network’s interface. Aiming on selectively removing fibre-fines from a streaming network by suction, we identify a reduction of the fines removal rate. That documents a hindered mobility of fibre-fines when moving through the network of fibres. Additionally, we found evidence, that the mobility of fibre-fines is dependent on the fibre-fines quality, and is higher for fibrillar fines. Consequently, we suggest that the quality of fibre-fines removed from the suspension can be controlled with the flow regime in the channel. Finally, we present a phenomenological model to compute the length dependent fibre distribution in an arbitary geometry. For a fibre suspension channel flow we are able to predict a length-dependent fibre segregation near the channel’s centre. The erosion of a plug of long fibres was however underestimated by our model. Interestingly, our model with parameters fitted to streaming fibre suspension qualitatively agreed with the motion of micro-fibrillated cellulose. This gives hope that devices for handling flocculated fibre suspensions can be designed in the future with greater confidence., QC 20211003

The concentration of fibers and fillers in the pulp suspension is an important parameter in the monitoring process. This paper proposes a versatile optical measurement system to estimate the concentration of a solids mixture in water. The geometry used in a multi-spectrophotometer (MSM) enables the controlled observation of transmission, and forward scattering light from the suspension in the UV-visible spectral range. We have developed the new fibers mixing system which gives a homogenous distribution of the fines and fillers making it possible to increase the reproducibility and accuracy of the measurement. The data analysis is based on the Beer-Lambert law and CIELAB color space equations. The results show that the proposed method is accurate for measuring the fines and filler concentrations in multicomponent suspensions.

Nanocellulosic coatings as a food packaging material are of commercial interest due to their nontox-ic nature, renewability, and excellent barrier properties. Complex shear-thinning rheology poses challenges in designing and sizing equipment to pump, mix, and process the suspension and actual coating process. This study aims to determine the effectiveness of computational fluid dynamics (CFD) in predicting nanocellulosic suspension flow in light of existing rheological data. We employ and compare three distinct rheological models to characterize the rheology and flow of nanocellulose suspensions through a slot die coater, where the model parameters are established from existing slot rheometry measurements. A volume-of-fluid (VoF) based finite volume method is employed to simulate the flow in a slot die operated in an unconventional metering mode. Results with the Casson model predict the presence of unyielded regions in the flow, which was not captured using the power law model. These stagnation regions will incur coatability issues stemming from flow intermittencies and lead to poten-tial defects in the coating layer, including fracture. The results suggest that a rheological model that includes yield stress should be considered while modeling such flows. A need for better rheological data to model nanocellulosic flows, especially at high consistencies and shear rates, is also highlighted. Application: This work identifies and clarifies the challenges to be addressed when considering industrial scale nanocellulose coating of paperboard.

One possible solution to reduce noise resulting from tyre-pavement interaction is to use a porous pavement surface. A porous surface will reduce noise by decreasing air pressure gradients in the tyre-pavement contact as well as by decreasing the acoustical impedance of the road surface and reducing the horn effect. While reducing noise, other functional aspects of a pavement such as abrasion wear which impacts on air pollution through generation and suspension of particles, friction and rolling resistance need to be addressed. This paper analyses the acoustical behaviour of a Double Layered Porous Asphalt (DLPA), applied in the city of Linköping, Sweden, as a solution to mitigate noise, compared to a non-porous Stone Mastic Asphalt (SMA) pavement used as reference. The analysis is based on Close Proximity noise measurements, both in absolute value and as frequency spectra, acoustical homogeneity over the surface length and sound absorption measurements. The acoustic analysis is combined with analyses of air quality measurements of PM10 (Particulate Matter with aerodynamic diameter < 10 µm) from two Tapered Element Oscillating Microbalance (TEOM) measurement stations placed near each different pavement section. The initial results indicate that the porous pavement results in a noise reduction of up to 5 dB for light vehicles, and up to 4 dB for heavy vehicles. So far, the DPLA shows approximately 52 % lower PM10 concentrations than the SMA. It should be noted that PM10 is influenced also by meteorological conditions, like humidity, background sources as well as vehicle properties, e.g. use of studded tyres, and that some of the observed decrease can be due to other aspects than porosity e.g. road surface moisture and wind direction. In conclusion, the use of a porous pavement shows promising results from both acoustical and air quality aspects, given the initial, short term results., QC 20200618

Monodisperse ensembles of particles that have cluster crystalline phases at low temperatures can model a number of physical systems, such as vortices in type-1.5 superconductors, colloidal suspensions, and cold atoms. In this work, we study a two-dimensional cluster-forming particle system interacting via an ultrasoft potential. We present a simple mean-field characterization of the cluster-crystal ground state, corroborating with Monte Carlo simulations for a wide range of densities. The efficiency of several Monte Carlo algorithms is compared, and the challenges of thermal equilibrium sampling are identified. We demonstrate that the liquid to cluster-crystal phase transition is of first order and occurs in a single step, and the liquid phase is a cluster liquid. © 2019 American Physical Society., Export Date: 24 May 2019; Article; Funding details: 621-2012-3984; Funding details: Vetenskapsrådet, 642-2013-7837; Funding text 1: W.W. and E.B. acknowledge support from the Swedish Research Council Grant No. 642-2013-7837 and the Goran Gustafsson Foundation for Research in Natural Sciences and Medicine. M.W. and R.D.M. acknowledge support from the Swedish Research Council Grant No. 621-2012-3984. The computations were performed on resources provided by the Swedish National Infrastructure for Computing (SNIC) at the National Supercomputer Centre (NSC) and the High Performance Computing Center North (HPC2N).

Interfaces divide all phases of matter and yet in most practical settings it is tempting to ignore their energies and the associated implications. There are many reasons for this, not the least of which is the introduction of a new pair of canonically conjugate variables-interfacial energy and its counterpart the surface area. A key set of questions surrounding the treatment of multiphase flows concerns how and when we must account for such effects. I begin this discussion with an abbreviated review of the basic theory of lower-dimensional phase transitions and describe a range of situations in which the bulk behaviour of a two-phase (and in some cases twocomponent) system is dominated by surface effects. Then I discuss a number of settings in which the bulk and surface behaviour can interact on equal footing. These can include the dynamic and thermodynamic behaviour of floating sea ice, the freezing and drying of colloidal suspensions (such as soil) and the mechanisms of protoplanetesimal formation by inter-particle collisions in accretion discs. This article is part of the theme issue 'The physics and chemistry of ice: Scaffolding across scales, from the viability of life to the formation of planets'. © 2019 Royal Society Publishing. All rights reserved., QC 20190710

Magnetorheological (MR) effect is a phenomenon typical of suspensions of magnetizable particles in a liquid carrier, characterized by strong changes of their mechanical properties in response to applied magnetic fields. Its origin is on the migration of magnetized particles and their aggregation into chain-like structures. However, for ferrogels, consisting of dispersions of magnetic particles in a polymer matrix, migration of particles is hindered by the elastic forces of the polymer network, preventing from strong MR effect. Interestingly, in this manuscript, we demonstrate that strong MR effect in robustly cross-linked polymer ferrogels is still possible. Experimental results showed enhancement of the storage modulus of more than one order of magnitude for alginate ferrogels containing less than about 10 vol% of iron particles under moderate magnetic fields. The differential feature of these ferrogels is that, instead of individual particles, the disperse phase consisted of large clusters of iron microparticles homogeneously distributed within the polymer networks. These clusters of magnetic particles were formed at the stage of the preparation of the ferrogels and their presence within the polymer networks had two main consequences. First, the volume fraction of clusters was considerably larger than this of individual particles, resulting in a larger effective volume fraction of solids. Second, since the force of magnetic attraction between magnetic bodies is roughly proportional to the cube of the body size, the existence of such clusters favored inter-cluster interaction under a magnetic field and the appearance of strong MR effect. On this basis, we demonstrated by theoretical modeling that the strong MR effect displayed by the alginate ferrogels of the present work can be quantitatively explained by assuming the existence of large, roughly spherical particle aggregates formed at the stage of the preparation of the ferrogels. Our theoretical model provides a

—The aggregation and sedimentation of ultradispersed diamonds (UDDs) in a citrate copper-plating electrolyte (CCPE) used to fabricate composite electrochemical coatings are investigated. The sedimentation and aggregation stability is investigated in order to select the UDD concentration in the CCPE. This is necessary to fabricate composite copper coatings with improved operational characteristics (increased hardness, wear resistance, and corrosion resistance), as well as impart them new properties (antifriction and catalytic). The UDD content in the electrolyte varies in limits from 0.2 to 2.0 g/L. The size distribution of the UDD particles in the electrolyte immediately after the suspension preparation and after the 10-day holding is determined using a Malvern Mastersizer 2000 laser diffraction analyzer. The aggregation and sedimentation stability of the UDD suspension in the CCPE is investigated by the gravimetric method with the continuous weighing of a quartz small cap immersed into this suspension. The quartz cap is associated with a Sartorius R200D analytical balance with the help of a quartz wire. The experimentally determined time dependence of the weight of settling UDD particles is Q = f(t). The relative size distribution of the particles is determined from this dependence. It is established that the sedimentation stability is substantially affected by the aggregation of the particles, the intensity of which increases with an increase in the UDD concentration. The results satisfying the requirements on the aggregation and sedimentation stability are found for the UDD suspension in the CCPE with a concentration of 1.0 g/L. In this case, the high content of the dispersed phase is combined with aggregation and sedimentation stability, which makes it possible to fabricate copper composite coatings with improved operational properties. © 2019, Allerton Press, Inc.

X-ray scattering is a promising non-invasive technique to study evolving nano- and micro-mechanics in clays. This study discusses the experimental considerations and a successful method to enable X-ray scattering to study clay samples at two extreme stages of consolidation. It is shown that the proposed sample environment comprising flat capillaries with a hydrophobic coating can be used for a wide range of voids ratios ranging from a clay suspension to consolidated clay samples, that are cut from larger specimens of reconstituted or natural clay. The initial X-ray scattering results using a laboratory instrument indicate that valuable information on, in principal evolving, clay fabric can be measured. Features such as characteristic distance between structural units and particle orientations are obtained for a slurry and a consolidated sample of kaolinite. Combined with other promising measurement techniques from Materials Science the proposed method will help advance the contemporary understanding on the behaviour of dense colloidal systems of clay, as it does not require detrimental sample preparation.

This study shows how to design an active suspension system for guidance of a rail vehicle wheelset in curve. The main focus of the study is on designing the controller and afterwards studying its effect on the wheel wear behaviour. The controller is designed based on the closed-loop transfer function shaping method and (Formula presented.) control strategy. The study discusses designing of the controller for both nominal and uncertain plants and considers both stability and performance. The designed controllers in Simulink are then applied to the vehicle model in Simpack to study the wheel wear behaviour in curve. The vehicle type selected for this study is a two-axle rail vehicle. This is because this type of vehicle is known to have very poor curving performance and high wheel wear. On the other hand, the relative simpler structure of this type of vehicle compared to bogie vehicles make it a more economic choice. Hence, equipping this type of vehicle with the active wheelset steering is believed to show high enough benefit to cost ratio to remain attractive to rail vehicle manufacturers and operators., QC 20201118

We study self-assembly in suspensions of supracolloidal polymer-like structures made of crosslinked magnetic particles. Inspired by self-assembly motifs observed for dipolar hard spheres, we focus on four different topologies of the polymer-like structures: linear chains, rings, Y-shaped and X-shaped polymers. We show how the presence of the crosslinkers, the number of beads in the polymer and the magnetic interparticle interaction affect the structure of the suspension. It turns out that for the same set of parameters, the rings are the least active in assembling larger structures, whereas the system of Y- and especially X-like magnetic polymers tends to form very large loose aggregates. © 2018 Elsevier B.V.

The objective of this work is to correlate the photocatalytic degradation of the herbicide imazapyr in aqueous suspensions of the commercially available Evonik Aeroxide TiO2 P25 with the dark adsorption phenomena considering both the equilibrium state and the kinetics of adsorption. The results of this study show that the adsorption of imazapyr onto the TiO2 surface is a second-order reaction and satisfies the criteria required by the Langmuir model. The adsorbed amount of imazapyr is found to be high at pH 3 and to decrease with increasing pH. The kinetics of the photocatalytic degradation of imazapyr were analysed taking into account the effect of the pH as well as of the catalyst mass concentration. However, special attention was focussed on the influence of the reactant concentration on the reaction rate. The Langmuir-Hinshelwood model fitting revealed that the apparent adsorption constant obtained under irradiation is significantly larger than the adsorption constant obtained in the dark. The initial reaction rates of the photocatalytic imazapyr degradation were larger than the initial adsorption rates of the probe molecule on the TiO2 surface. It is therefore concluded that the photocatalytic imazapyr degradation does not follow necessarily a Langmuir-Hinshelwood mechanism despite the fact that a rate law having the mathematical form of the Langmuir-Hinshelwood rate law was successfully used to describe the observed dependence of the initial reaction rates on the initial concentrations. A Langmuir-Hinshelwood mechanism for the photocatalytic imazapyr degradation is compatible only with the additional assumption that the rate constant of adsorption increases by irradiation with UV light. © 2018 The Royal Society of Chemistry.

The viscosity of low SiO2 (10–20 mass%)-CaO-Al2O3 slag system was measured in a wide temperature range (1 623–2 800 K) using the rotational bob method and the aerodynamic levitation method. The influence of SiO2/Al2O3 ratio and CaO/Al2O3 ratio on the viscosity was examined. It was concluded that the SiO2/Al2O3 ratio did not affect the degree of polymerization of the aluminosilicate network in the composition range of the present study. An abnormal behaviour of the viscosity was observed at a CaO/Al2O3 ratio of 1.57 which was attributed to the formation of 12CaO·7Al2O3-like clusters. It was concluded that the overall influence on the viscosity could be expressed as the summation of the influence from the aluminosilicate network and the influence from the cluster formation of the primary precipitating solid phase. The temperature dependence of the cluster formation was coupled to the driving force of precipitation of the 12CaO·7Al2O3 phase.

The influence of structure and charge of particles surfaces on the cake filtration behaviour of microcrystalline cellulose was investigated. The local filtration properties were evaluated experimentally and used to model the overall filtration behaviour. At suspension conditions where the microcrystalline cellulose particles are charged, a large pressure drop was observed close to the filter medium, thereby indicating that a rate-limiting skin layer was formed. Measurements of the local solidosity of the filter cake indicated that a secondary filter cake, with a negligible filtration resistance, formed above the rate-limiting skin layer. This behaviour was not observed when the surface roughness of the particles was increased or when the surface charge of the particles was neutralised by making a change to the pH of the suspension. The filtration behaviour of particles with these surface properties was instead dominated by the formation of a compressible filter cake. Local filtration properties of compressible filter cakes determined experimentally were used to successfully model the overall filtration behaviour. The filtration model used an empirical relationship to describe the pressure dependence of the local solidosity of the filter cake along with a cell model to describe the relationship between the solidosity and the permeability of the filter cake., QC 20170524

The interesting magnetic response of conventional ferro-colloid has proved extremely useful in a wide range of technical applications. Furthermore, the use of nano/micro- sized magnetic particles has proliferated cutting-edge medical research, such as drug targeting and hyperthermia. In order to diversify and improve the application of such systems, new avenues of functionality must be explored. Current efforts focus on incorporating directional interactions that are surplus to the intrinsic magnetic one. This additional directionality can be conveniently introduced by considering systems composed of magnetic particles of different shapes. Here we present a combined analytical and simulation study of permanently magnetized dipolar superball particles; a geometry that closely resembles magnetic cubes synthesized in experiments. We have focused on determining the initial magnetic susceptibility of these particles in dilute suspensions, seeking to quantify the effect of the superball shape parameter on the system response. In turn, we linked the computed susceptibilities to the system microstructure by analyzing cluster composition using a connectivity network analysis. Our study has shown that by increasing the shape parameter of these superball particles, one can alter the outcome of self-assembly processes, leading to the observation of an unanticipated decrease in the initial static magnetic susceptibility. © 2017 American Chemical Society.

Micron-sized particles (microbeads) dispersed in a suspension of magnetic nanoparticles, i.e., ferrofluids, can be assembled into different types of structures upon application of an external magnetic field. This paper is devoted to theoretical modeling of a relative motion of a pair of microbeads (either soft ferromagnetic or diamagnetic) in the ferrofluid under the action of applied uniform magnetic field which induces magnetic moments in the microbeads making them attracting to each other. The model is based on a point-dipole approximation for the magnetic interactions between microbeads mediated by the ferrofluid; however, the ferrofluid is considered to possess an anisotropic magnetic permeability thanks to field-induced structuring of its nanoparticles. The model is tested against experimental results and shows generally better agreement with experiments than the model considering isotropic magnetic permeability of ferrofluids. The results could be useful for understanding kinetics of aggregation of microbeads suspended in a ferrofluid. From a broader perspective, the present study is believed to contribute to a general understanding of particle behaviors in anisotropic media. © 2017 American Physical Society.

The present paper is focused on the theoretical and experimental study of the kinetics of field-induced aggregation of magnetic nanoparticles of a size range of 20-100 nm. Our results demonstrate that (a) in polydisperse suspensions, the largest particles could play a role of the centers of nucleation for smaller particles during the earliest heterogeneous nucleation stage; (b) an intermediate stage of the aggregate growth (due to diffusion and migration of individual nanoparticles towards the aggregates) is weakly influenced by the magnetic field strength, at least at high supersaturation; (c) the stage of direct coalescence of drop-like aggregates (occurring under magnetic attraction between them) plays a dominant role at the intermediate and late stages of the phase separation, with the time scale decreasing as a square of the aggregate magnetization. © 2017 Author(s).

Micrometer-sized vapor-gas bubbles are formed due to local heating of a water suspension containing absorptive pigment particles of 100 nm diameter. The heating is performed by CW near-infrared (980 nm) laser radiation with controllable power, focused into a 100 mu m spot within a 2 mm suspension layer. By changing the laser power, four regimes are realized: (1) bubble generation; (2) stable growth of the existing bubbles; (3) stationary existence of the bubbles and (4) the bubbles' shrinkage and collapse. This behavior is interpreted based on the temperature conditions. The generation and evolution of single bubbles and ensembles of bubbles with controllable sizes and numbers is demonstrated. The bubbles are grouped within the laser-illuminated region and form quasi-ordered structures. They can easily be moved and transported controlled by the focal spot. The results are useful for applications associated with the precise manipulation, sorting and specific delivery in nano- and micro-engineering problems. (C) 2017 Optical Society of America