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The viscoelastic behaviors of aqueous solutions of commercially available methyl cellulose (MC) samples with a degree of substitution of 1.8 and a wide range of weight average molar masses (Mw) were investigated over a wide concentration (c) range at some temperatures from −10 to 25 °C. The viscoelastic parameters useful to discuss the structure and dynamics of MC-forming particles in aqueous solutions were precisely determined, such as the zero-shear viscosity (η0), the steady-state compliance (Je), the average relaxation time (τw), and the activation energy (E*) of τw. Because previously obtained scattering and intrinsic viscosity ([η]) data revealed that the MC samples possess a rigid rod-like structure in dilute aqueous solutions over the entire Mw range examined, the viscoelastic data obtained in this study were discussed in detail based on the concept of rigid rod particle suspension rheology. The obtained Je−1 was proportional to the number density of sample molecules (ν = cNAMw−1, where NA means the Avogadro's constant) over the ν range examined irrespective of Mw. The reduced relaxation time (4NAτw(3νJe [η]ηmMw)−1), where ηm means the medium viscosity, was proportional to (νL3)2, L; the average particle length depending on Mw for each sample was determined in a previous study; and the reduced specific viscosity (ηspNAL3(Mw [η])−1), where ηsp means the specific viscosity, was proportional to (νL3)3 in a range of νL3 < 3 × 102. These findings were typical characteristics of the rigid rod suspension rheology. Therefore, the MC samples behave as entangling rigid rod particles in the νL3 range from rheological points of view. A stepwise increase in E* was clearly observed in a c range higher than the [η]−1 value irrespective of Mw. This observation proposes that contact or entanglement formation between particles formed by MC molecules results in an increase in E*. [ABSTRACT FROM AUTHOR]

The effect of resting time on the rheological properties of cement suspensions is generally explained by early formed structure and overconsumption of polycarboxylate superplasticizers (PCEs). In this paper, we propose that the influence of resting time on the rheological properties is closely related to size variation of non‐absorbed PCE. To identify this, glass bead suspensions were prepared with various amounts of PCE and ionic solution, and their rheological properties were evaluated at various times. We found that the yield stress increases with time at higher PCE concentrations and higher ionic strength solutions. Adsorbed PCE during resting tends to bridge the particles rather than disperse them. In addition, it was found that hydrodynamic radius of PCE increased with resting time, and depletion forces resulting from non‐absorbed PCE size changes correlate well with the increased yield stress. [ABSTRACT FROM AUTHOR]

To obtain a complete understanding of the properties of cellulose nanocrystal (CNC) suspensions, we not only need to be able to characterize the CNCs themselves but also be able to analyze their particle-particle interactions and spatial distribution. Here, three established techniques—dynamic light scattering, rheology and atomic force microscopy (AFM)—and two new techniques—interferometric scattering (iSCAT) microscopy and cluster-triggered emission (CTE) autofluorescence spectroscopy—are evaluated for their ability to determine whether a CNC suspension is well-dispersed. This study confirms that AFM height data, rheology, iSCAT microscopy and CTE autofluorescence spectroscopy are sensitive to the transition from agglomerates to individual CNCs, validating their suitability. Data from these four techniques also indicate that excessive sonication of CNC suspensions is feasible, potentially leading to undesirable nanoparticle degradation. These results confirm the applicability of both iSCAT microscopy and CTE autofluorescence spectroscopy for high throughput analysis of nanoparticle dispersion, which can potentially be employed during the industrial production of CNCs. [ABSTRACT FROM AUTHOR]

Alumina ceramics with optimized microstructures and mechanical properties were obtained by the attractive digital lighting processing (DLP) additive manufacturing methodology in the present study. A acrylate-based resin system was designed for the alumina powders with a mean particle size of 0.5 μm. The influence of oligomer on the viscosity and polymerization kinetics of the ceramic suspensions has been elaborately discussed by rheology, curing depth and photo-DSC characterizations. The results indicated that the introduction of oligomer has improved the cross-linking density of resins and decreased the critical dose of energy for resin polymerization, which contributed to a tougher ceramic-resin slice with higher dimensional accuracy. Densifying processes including debinding and high temperature sintering of the ceramic parts were conducted according to the TG-DTA characterizations, alumina ceramics with uniform microstructures and eliminated delamination or intralaminar cracks were finally obtained. The flexural strength was 471 MPa for the ceramics obtained from the resin composition containing 20 wt% oligomer, Weibull modulus for the ceramics were determined to be 17.31 by evaluating thirty all sides polished ceramics, indicating the highly uniform property of the ceramics fabricated by DLP additive manufacturing. [ABSTRACT FROM AUTHOR]

[Display omitted] Despite their apparent simplicity, suspensions of hard spheres in a Newtonian fluid show complex non-Newtonian behaviors and remain poorly understood. Recent works have pointed out the crucial role of interparticle contact forces in these behaviors. Here, we show that the same (polystyrene) particles, when immersed in different Newtonian solvents, show different behaviors at both the microscopic and macroscopic scales. Thanks to interparticle force measurements in each solvent together with rheological measurements, we show how the fine details of the pairwise particle interactions impact the macroscopic behavior. The rheological properties (shear thinning, shear thickening, jamming solid fraction value) of the suspensions, made up of same particles, are shown to depend on the nature of the solvent. Here, we highlight several mechanisms at the particle scale: the swelling of polymeric particles in an organic solvent, the role of colloidal repulsive forces and inertia for particles in a water solution, and the variation of the friction coefficient as a function of the load for particles immersed in silicone oils. Our study provides new quantitative data to test micromechanical models and simulations. It questions the interpretation of previous experimental works. Finally, it shows the need to systematically characterize the interparticle normal and tangential forces when studying a given suspension of hard spheres in a Newtonian fluid [ABSTRACT FROM AUTHOR]

We report the linear rheology for dense suspensions of sterically stabilized smooth and mesoscopically rough colloids interacting as hard particles. Small amplitude oscillatory measurements reveal that rough colloids at high volume fractions exhibit storage and loss moduli that are orders of magnitude greater than smooth colloids. Frequency-concentration superposition is used to collapse the viscoelasticity data onto a master curve, where shift factors suggest a more elastic microstructure and reduced cage volume for rough particles. A combination of the mode-coupling theory, hydrodynamic modeling, and the activated hopping theory shows that these rough particles with significantly reduced localization lengths tend to become trapped in their glassy cages for extended periods of time. High-frequency data show that rough colloids, but not smooth colloids, display a transition from a free-draining to a fully lubricated state above the crossover volume fraction and, furthermore, exhibit solidlike behavior. Scaling analyses support the idea that lubrication forces between interlocking asperities are enhanced, leading to rotational constraints and stress-bearing structures that significantly elevate the viscoelasticity of dense suspensions. The results provide a framework for how particle surface topology affects the linear rheology in applications such as coatings, cement, consumer products, and shock-absorbing materials. [ABSTRACT FROM AUTHOR]

Understanding rheological properties of dispersions of cellulose nanomaterials such as cellulose nanofiber (CNF) and cellulose nanocrystal (CNC) has received tremendous attentions from scientific and industrial viewpoints. To gain insight into the effect of aggregation-dispersion of CNF on the sol–gel state of aqueous CNF suspensions, simple turnover tests were performed for semi-dilute CNF suspensions as a function of pH and potassium chloride (KCl) concentration. Experimental results revealed that the gel state was confirmed around 20–100 mM KCl depending on pH, and the sol state was observed at higher or lower KCl concentrations. The upper and lower boundaries between gel and sol states were 20 and 80 mM around pH 4, and 50 and 120 mM around pH 7. These boundaries were discussed using the angle-dependent Derjaguin-Landau-Verwey-Overbeek (DLVO) theory for cylindrical particles. From the discussion, we presume that the gel of semi-dilute CNF suspension can be formed when the aggregation is allowed at the orientation angle between 45 and 90°. Aggregation at orientation angles below 30° can occur at high KCl concentration and might result in sol state due to the formation of aggregate with compact structure, which cannot allow the network structure in the whole suspension. [ABSTRACT FROM AUTHOR]

Background. The increased content of low-grade sylvinite leads to a low indicator of product quality and the recovery factor of the main component - potassium chloride. In this regard, the problem of processing low-grade sylvinite from the Tyubegatanskoye deposit is relevant for the potash enterprise. Purpose. The aim of the study is to study the influence of technological parameters on the process of crystallization of potassium chloride and to determine the optimal conditions for obtaining potassium chloride by the halurgical method of enrichment of low-grade sylvinite of the Tyubegatanskoye deposit. Methodology. The solubility of low-grade sylvinite in water has been studied. When performing the work, standard methods of chemical analysis were used. The identification of solid phases was carried out by the method of physicochemical analysis. Originality. For the first time, the influence of time, the ratio of low-grade sylvinite to water, temperature and cooling rate on the crystallization of potassium chloride was studied, and the rheological properties of suspensions obtained by dissolving low-grade sylvinite in water were studied. Findings. Chemical and X-ray phase analyzes established the composition of the initial components and products of potassium chloride obtained by dissolving low-grade sylvinite in water. [ABSTRACT FROM AUTHOR]

Cellulose nanocrystals (CNCs) are rapidly increasingly used nanomaterials with a large surface area, outstanding mechanical characteristics, and the capacity to exhibit variable surface chemistry, allowing them to be incorporated into a variety of matrices. An examination of information from various firms on scales of tonnes per day suggests an increasing tendency for the use of CNC-based products. Here, we review recent advances in microstructural characterization of CNC-based suspensions and hydrogels utilizing imaging and rheological approaches. We demonstrate how microscopy and rheology can be utilized to adjust and improve the final macro characteristics of CNC-based systems. Novel applications, e.g., 3D printing, for CNC suspensions and gels are also introduced. Indeed, because CNC-based products show significant potential for biomedical, energy, cosmetics, filtration, and food applications, using existing characterization methods and models to fine-tune the CNC colloid properties cannot be ruled out. All references were selected from recent publications (earlier than 2010). [ABSTRACT FROM AUTHOR]

Today, graphene oxide (GO) has gained well-deserved recognition, with its applications continuing to increase. Much of the processing of GO-based devices occurs in a dispersed form, which explains the commercialization of GO suspensions. Aging of these suspensions can, however, affect the shelf life and thus their application potential. Aging of GO preparations is often acknowledged, but no longer-term systematic study has been reported on the alteration of GO suspensions. This paper investigates high-concentration (10 mg/mL) aqueous GO suspensions over a 2-year time scale. In addition to steady shear tests, the dynamic behavior of the suspensions was studied in more detail by transient shear and frequency sweep measurements. Both the viscosity and the dynamic moduli increased with age, particularly within the first year. The results of the complementary Raman spectroscopic studies indicate that the change in the rheological behavior with aging results from a slow oxidation process occurring in the highly acidic aqueous medium during the relatively long-term storage. The (over)oxidized layers peel off spontaneously or are removed by high shear stress, resulting in increased viscosity, as it was corroborated by XRD and XPS. [ABSTRACT FROM AUTHOR]

Background: Ibuprofen a nonsteroidal anti-inflammatory drug (NSAID) derived from propionic acid utilized for its anti-inflammatory and analgesic effect was selected as an active substance for incorporation into hydrogel matrices since this active ingredient is recommended for pain therapy, rheumatoid arthritis, and osteoarthritis. Objective: The purpose of this study is to develop and optimize a suspension-type gel containing 5% ibuprofen using a full factorial design and to highlight and optimize the rheology and consistency of the products. Material and methods: In this study, the following substances were used: ibuprofen 5%, sodium carboxymethylcellulose (CMCNa, gel-forming agent), glycerol (humectant), menthol (penetration enhancer), alcohol (co-solvent), and preservative solution. Using Modde 13 software, a full factorial 22 design with 3 central points resulting in 7 formulations was applied, where the gel-forming agent and the humectant represented independent variables as follows: GI1 (CMCNa 2.5g, glycerol 2g), GI2 (CMCNa 2.5g, glycerol 3g), GI3 (CMCNa 5g, glycerol 2g), GI4 (CMCNa 5g, glycerol 3g), and three central points GI5, GI6, GI7 (CMCNa 3.75g, glycerol 2.5g). The remaining substances were added in equal amounts to all gels. The outputs selected were consistency, spreadability, shear stress, and viscosity at shear rates of 6 and 12 during both shear thinning and recovery phases. Results : The evaluated statistical parameters include R² (coefficient of determination) and Q² (measuring the predictive ability of the model), model validity, and reproducibility. All dependent variables exhibit positive predictability values, and all selected inputs highlight an R² close to 1, besides, the validity being > 0.25 indicates the lack of fit of the model. Increasing the concentration of the gel-forming agent produced a significant decrease in the spreadability and consistency while for the outputs selected during the destructuration and restoration phase (viscosity and tangential stress), a complex correlation behavior was noticed. The results obtained from the rheological test were graphically represented, indicating a pseudoplastic thixotropic flow. Conclusions: In conclusion, this study has demonstrated the success of utilizing a full factorial 22 design for the development of an optimal formulation of 5% ibuprofen gel, used in the treatment of local pain. Through the evaluation of 7 formulations, an optimal formulation with specific concentrations of sodium carboxymethylcellulose and glycerol was assessed, which provides the desired characteristics of spreadability, consistency, viscosity, and tangential stress. [ABSTRACT FROM AUTHOR]

This study investigated the rheological properties of cellulose nanocrystal (CNC) suspensions in carboxymethylcellulose (CMC) polymer solutions by studying steady shear viscosities, linear viscoelastic behaviors, applicability of the Cox–Merz rule, and time-dependent behavior. The rheological measurement showed that interactions between CNC and CMC resulted in liquid crystalline domains and a substantial increase in viscosity, shear-thinning, elasticity, and thixotropy. Depletion flocculation formed a percolated structure of liquid crystalline domains, resulting in a gel-like structure, which was evidenced by polarized optical microscopy. The strong effects on rheological properties by mixing small quantities of CMC and CNC suggest that this system may find applications where tunable rheological properties of aqueous polymeric systems are desirable. [ABSTRACT FROM AUTHOR]

Suspensions of calcium carbonate are of a major concern in various fields, such as coating, painting and ceramics and their rheological properties are very important. The effect of polyacrylic acid (PAA) of different molecular mass as a surface modifier on the surface and rheological properties of the aqueous suspension of calcium carbonate was investigated. The effect of the volume fraction of particles and polymer concentration on the viscosity at lower shear rate was discussed. The flow behavior of the concentrated suspension in the presence of PAA can be explained by the difference of the repulsive force among particles, induced by the adsorbed polymer. The results showed that the dispersibility is more pronounced by the steric hindrance behavior rather than the electrostatic behavior. [ABSTRACT FROM AUTHOR]

INTRODUCTION: Hydroxyapatite (HAP), a crucial constituent of natural bone mineral, significantly enhances the osteoconductivity of alginate hydrogels (AH) in biodegradable composites mimicking the mineral composition, porosity, and mechanical properties of bone tissue. Ionic crosslinking of sodium alginate hydrogels with Ca+ ions result in the rapid formation of egg-box structures, leading to enthalpy-driven hydration and dehydration mechanisms observable through swelling and subsequent shrinkage of the crosslinked aerogel. The fast shrinkage induces non-linear sizing of water-containing pockets, impacting the unilinear pore size distribution of freeze-dried aerogels, thereby influencing the porosity and mechanical properties of the final scaffolds. EXPERIMENTAL: Kinetics of gel-sol phase transformations of 2 % AH gel with fixed amount of mixture of hydroxyapatite (HAP) in 2 % CaCl2 water bath with mass ratios of HAP to CaCl2 (100:0, 35:75, 50:50, 75:35 and 0:100 respectively) was observed on a plate-plate Anton Paar 302 rheometer. Viscoelastic measurements were conducted in linear viscoelastic region (LVE) with constant strain (γ = 0.1 %) and varying angular frequencies (ω= 0.1, 0.5 and 1 rad. s-1 that simulated different mixing rates. Once that viscoelastic parameters (Transient complex viscosity (η*+ ), Storage modulus (G´) and Loss modulus (G´´)) reached their plateau values, samples were removed from rheometer were freeze dried for morphological observation with Scanning electron microscope (SEM) Hitachi S-4700, (Chiyoda City, Tokyo, Japan). RESULTS AND DISCUSSION: Kinetic of Ca+ ions induced crosslinking of alginate hydrogels is a complex, non-linear process governed by colloidal forces and change in system enthalpy, dependent on ions concentration and mixing frequency. Stepwise process of adsorption of Ca2+ ions onto HAP particles and their release into sodium alginate hydrogel results in nonlinear time-dependent crosslinking kinetic dependent on suspension ions concentration and mixing rate followed by reversable hydration and dehydration. Formation of smaller egg-box structures that contain interlocked water is observable through change in rheological parameters and in structure of freeze-dried aerogels. CONCULSIONS: Step-wise adsoption of Ca+ ions ono HAP particles in CaCl2 suspension, enables their controlled release once the suspension is poured into sodium alginate hydrogel and formation of uniform pores size distribution. [ABSTRACT FROM AUTHOR]

We study the viscoelastic solid properties of cohesive particulate suspensions using creep and constant rate tests in a vane-in-large-cup geometry. A cup-to-vane diameter ratio larger than 4 is used to ensure that wall effects are minimized. In both the creep and constant rate tests, the modulus becomes nonlinear at strains consistent with scaled interparticle bond distances. Yielding and subsequent flow do not occur until strains of order 1, corresponding to a cage melting or particle crowding failure mechanism. In between the bond and cage melting strains, the modulus shows power-law softening with an index of approximately −0.8, corresponding to progressive bond breakage. The observed behavior in creep correlates with constant rate experiments and demonstrates that strain softening of the modulus prior to yielding is an important component of the rheology of particulate gels and suspensions. The assumption of linear behavior up to yielding appears to be inappropriate. We observe that the transient creep behavior initially shows power-law or Andrade creep that transforms to an exponential decay at long times. For creep stresses that show time-dependent yield, the break time decreases exponentially with stress. [ABSTRACT FROM AUTHOR]

Vat photopolymerization is an additive manufacturing process that produces high-performance ceramic parts. A critical step in the process is the preparation of a suspension that meets the requirements of high ceramic loading and proper rheological behavior, since an increase in solid loading might compromise the suspension rheology, resulting in non-uniform layer recoating. This review examines the rheological behavior of ceramic suspensions for vat photopolymerization, discussing the influence of the suspension formulation (solid loading, ceramic particle size and size distribution, monomers, diluents, and dispersants) on rheological aspects such as viscosity, shear-thinning/thickening behavior, critical shear rate, yield stress, and thixotropy. It provides a summary of the best formulations, which achieved low viscosity (<3 Pa.s) and high solid loading (>40 vol%), and reports the main trends and challenges of ceramic vat photopolymerization, suggesting general guidelines for the preparation of highly loaded photocurable ceramic suspensions with low viscosity. [ABSTRACT FROM AUTHOR]

Although the rheology of cellulose nanocrystalline (CNC) suspensions has been widely studied, less attention has been paid to the modified cellulose nanocrystals such as cationic and anionic cellulose hydrogels. In this work, the rheological behavior of cellulose nanocrystals (CNCs), anionic CNCs (pCNCs), and cationic CNCs (nCNCs), was comparatively studied. The rheological behavior demonstrated that the nCNC and pCNC form hydrogen bonding, which significantly contributes to the increase in the gel strengths in the sonicated state. The formation of such structures between individual fibers prevents flocculation due to the increased suspension stability. In addition, the extensive formation of hydrogen bonding in the case of nCNC compared to that of pCNC explains its enhanced rheological properties. The effect of pre-shear has been studied in detail for these systems by considering a combination of pre-shear and startup of steady shear in different shearing directions with certain rest/recovery time in between to eliminate strain history and thus eliminate the possible bias of pre-shearing on structure formation. [ABSTRACT FROM AUTHOR]

Single walled carbon nanotubes, SWCNTs, are used as a model cylinder of nanoscopic dimensions for testing rheological theories of how addition of cylindrical particles affects the viscosity of a suspension of such particles. Using the rate of growth of the accompanying induced linear dichroism following application of an applied electric field, the dynamics of carbon nanotube alignment is studied in suspensions of octadecylamine functionalised single walled carbon nanotubes, ODA-SWCNTs, in 1,2 dichloroethane. From such measurements the viscosity of the suspension is measured as the concentration of the suspension is varied. While working within the dilute limit the viscosity is found to increase linearly with concentration and the intrinsic viscosity of the suspension is found to be 8000. This anomalously high intrinsic viscosity is compared with the predictions of various models for a rigid cylinder and found to be incompatible with any of the current models. Some suggestions are made as to the way this ODA-SWCNT result may be eventually accommodated within other models. [ABSTRACT FROM AUTHOR]

Protein-stabilised emulsion gels can be studied in the theoretical framework of colloidal gels, because both protein assemblies and droplets may be considered as soft colloids. These particles differ in their nature, size and softness, and these differences may have an influence on the rheological properties of the gels they form. Pure gels made of milk proteins (sodium caseinate), or of sub-micron protein-stabilised droplets, were prepared by slow acidification of suspensions at various concentrations. Their microstructure was characterised, their viscoelasticity, both in the linear and non-linear regime, and their frequency dependence were measured, and the behaviour of the two types of gels was compared. Protein gels and droplet gels were found to have broadly similar microstructure and rheological properties when compared at fixed volume fraction, a parameter derived from the study of the viscosity of the suspensions formed by proteins and by droplets. The viscoelasticity displayed a power law behaviour in concentration, as did the storage modulus in frequency. Additionally, strain hardening was found to occur at low concentration. These behaviours differed slightly between protein gels and droplet gels, showing that some specific properties of the primary colloidal particles play a role in the development of the rheological properties of the gels. [ABSTRACT FROM AUTHOR]

Various species of the genus Grewia have been investigated for different pharmaceutical applications as excipients, yet a study on the potential use of Grewia ferruginea mucilage (GFM) as a suspending agent is lacking. Thus, this study is aimed at evaluating the efficacy of Grewia ferruginea mucilage (GFM) as a suspending agent in metronidazole benzoate suspension. The suspensions were prepared using 0.5%, 1%, 1.5%, and 2% w / v of GFM and compared with suspensions prepared from xanthan gum (XGM) and sodium carboxyl methyl cellulose (SCMC) in similar concentrations. The prepared suspensions were evaluated for visual appearance, pH, rheology, sedimentation volume, redispersibility, degree of flocculation, and in vitro drug release profile. Stability study was done at different storage conditions for three months. The results indicated that all the prepared suspension formulations exhibited pseudoplastic flow characteristics with viscosity imparting ability of the suspending agents in the order of XGM > GFM > SCMC (p < 0.05). The flow rate and redispersibility of the formulations prepared with GFM were significantly lower than those with SCMC and higher than those prepared with XGM. At 0.5% w / v suspending agent concentrations, the sedimentation volume of the formulations was in the order of XGM > GFM > SCMC (p < 0.05). However, at all other concentrations, the sedimentation volume of the formulations prepared with GFM had similar results with XGM but exhibited significantly higher sedimentation volume than SCMC. The formulations with GFM showed a higher degree of flocculation at 0.5% w / v concentration but were comparable at 1.5% w / v with XGM containing formulations. The pH, assay, and in vitro release profile of all assessed formulations were within the pharmacopial limit. Thus, based on the finding of this study, it can be concluded that Grewia ferruginea bark mucilage has the potential to be utilized as a suspending agent in suspension formulations. [ABSTRACT FROM AUTHOR]

Aqueous suspension of polyisobutylene (PIB) was stabilized via application of anionic surfactant of sodium lauryl sulfate (SLS) and co-surfactants of stearyl and cetyl alcohols. Suspensions were produced via the so-called direct emulsification technique. Some characterization tests including zeta potential, particle size, turbidity, conductivity, and rheology measurements were demonstrated to analyze the stability of produced suspensions. Turbidity and particle size measurements showed that just some of the samples were stable while the others exhibited partial aggregation of particles. The characterization tests showed that the sample contained 2 g of polyisobutylene, 0.45 g SLS, 0.175 g stearyl, and 0.263 g cetyl alcohols, i.e., co-surfactant ratio of 0.66, in 80 mL of water exhibited appropriate stability. Possession of high zeta potential of − 93.65 mV, conductivity of 570 mS/cm, an average particle size of 10 μm, and good rheological behavior besides the stable appearance revealed that this sample did not undergo agglomeration, flocculation, or any phase separation. [ABSTRACT FROM AUTHOR]

The liquid crystalline and rheological properties of chitin whiskers (CHWs) are significant for their application in fabrication of highly ordered composite materials and optical components. The aim of this work was to elucidate the influence of chemical structure and chargeability (zeta potential, electropositivity, electronegativity or zwitterionic character) on the liquid crystalline and rheological properties of CHWs. Firstly, CHWs with different chemical structure, including positively charged whiskers (CHWs and CHWs-D/60 min) and negatively charged whiskers (mCHWs), were designed via acid hydrolysis, deacetylation, and maleation, respectively. Subsequently, the chargeability of the above whiskers was further regulated by protonation or deprotonation. The whisker aqueous suspensions with high zeta potential behaved as nematic liquid crystals or chiral nematic liquid crystals, whereas those with low zeta potential had no liquid crystal characteristics. The viscosity, G', and G" values of the CHWs and CHWs-D/60 min aqueous suspensions treated with protonation were lower than those of the corresponding whiskers treated with deprotonation. However, the mCHWs exhibited different changes in their rheological properties under protonation or deprotonation due to the electronegativity and zwitterionic characteristics. In addition, the effects of ionic strength and pH on the liquid crystalline and rheological properties of CHWs, CHWs-D/60 min, and mCHWs aqueous suspensions varied since the chemical structure and chargeability of whiskers differ. • CHWs with different chemical structures and chargeabilities were designed. • The chargeability of whiskers can be further regulated by pH or ionic strength. • Different charged CHWs suspension showed various liquid crystal behavior. • The liquid crystal behavior of CHWs depended on interactions between whiskers. • The interactions between CHWs correlated with the chargeabilities of whiskers. [ABSTRACT FROM AUTHOR]

The zeta potential data confirmed the adsorption of the large compact Keggin [Si(W 12 O 40)]4- and heteropolytungstate (LST) anions on both α-Al 2 O 3. The adsorbed [Si(W 12 O 40)]4- ions should form a thick steric barrier, ~1 nm, but this effect was not reflected in the yield stress results. A relatively strong additional attractive force explained the increasing maximum yield stress. A similar result was observed with LST. For the spherical α-Al 2 O 3 the largest maximum yield stress (at zero charge) occurred at 0.6 dwb% additive. This attractive force was attributed to patch charge attraction between the negative additive patch and the positive surface site. For the low surface area platelet α-Al 2 O 3 suspensions, complete surface coverage occurred at a low additive concentration as reflected by an almost identical all negative zeta potential-pH behaviour at all additive concentrations at low pH. The slightly larger yield stress at pH 2.5 could be due to this patch charge bridging attraction. Image 1 • Large [SiW 12 O 40 4- and LST ions increase the gel strength of α-Al 2 O 3 suspensions. • Patch charge bridging (PCB) was responsible for the increased gel strength. • The thick hard wall steric effect is relatively unimportant compared to the PCB effect. [ABSTRACT FROM AUTHOR]

A direct consequence of the finite compressibility of a swollen microgel is that it can shrink and deform in response to an external perturbation. As a result, concentrated suspensions of these particles exhibit relaxation dynamics and rheological properties which can be very different with respect to those of a hard sphere suspension or an emulsion. We study the reduction in size of ionic microgels in response to increasing number of particles to show that particle shrinkage originates primarily from steric compression, and that the effect of ion-induced de-swelling of the polymer network is negligible. With increasing particle concentration, the single particle dynamics switch from those typical of a liquid to those of a super-cooled liquid and finally to those of a glass. However, the transitions occur at volume fractions much higher than those characterizing a hard sphere system. In the super-cooled state, the distribution of displacements is non-Gaussian and the dependence of the structural relaxation time on volume fraction is describable by a Volger-Fulcher-Tammann function. [ABSTRACT FROM AUTHOR]

Short-time dynamic properties of concentrated suspensions of colloidal core-shell particles are studied using a precise force multipole method which accounts for many-particle hydrodynamic interactions. A core-shell particle is composed of a rigid, spherical dry core of radius a surrounded by a uniformly permeable shell of outer radius b and hydrodynamic penetration depth κ-1. The solvent flow inside the permeable shell is described by the Brinkman-Debye-Bueche equation, and outside the particles by the Stokes equation. The particles are assumed to interact non-hydrodynamically by a hard-sphere no-overlap potential of radius b. Numerical results are presented for the high-frequency shear viscosity, η∞, sedimentation coefficient, K, and the short-time translational and rotational self-diffusion coefficients, Dt and Dr. The simulation results cover the full three-parametric fluid-phase space of the composite particle model, with the volume fraction extending up to 0.45, and the whole range of values for κb, and a/b. Many-particle hydrodynamic interaction effects on the transport properties are explored, and the hydrodynamic influence of the core in concentrated systems is discussed. Our simulation results show that for thin or hardly permeable shells, the core-shell systems can be approximated neither by no-shell nor by no-core models. However, one of our findings is that for κ(b - a) >= 5, the core is practically not sensed any more by the weakly penetrating fluid. This result is explained using an asymptotic analysis of the scattering coefficients entering into the multipole method of solving the Stokes equations. We show that in most cases, the influence of the core grows only weakly with increasing concentration. [ABSTRACT FROM AUTHOR]

We study the rheology of model colloidal suspensions using molecular-dynamics simulations. We relate the onset of shear thickening to the transition from a low-viscosity regime, in which the solvent facilitates the flow of colloids, to a high-viscosity regime associated with jamming of the colloids and the formation of chains of colloids. In the low-viscosity regime, the colloidal particles are, on average, surrounded by two layers of solvent particles. On the contrary, in the high-viscosity regime, the solvent is expelled from the interstice between the jammed colloids. The thickening in suspensions is shown to obey the same criterion as in simple fluids. This demonstrates that jamming, even without the divergence of lubrication interactions, is sufficient to observe shear thickening. [ABSTRACT FROM AUTHOR]

Tapioca starch (TS) suspensions (10%, w/v) were subjected to high speed jet (HSJ) processing at 80, 120, 160, 200 and 240 MPa for one pass, and the effects of HSJ treatment on solubility, rheological, pasting, morphological and molecular properties were further investigated. Polarized light microscopy observation revealed TS was partly gelatinized, and the number and clarity of"Maltese cross" decreased with the increase of HSJ pressure. The solubility of TS was increased significantly from 1.59% (0 MPa) to 12.11% (240 MPa). Dynamic oscillation analysis showed that TS gels displayed less elastic and more liquid like after HJS treatment, and all samples displayed pseudo-plastic properties during flow properties analysis. Rapid Visco Analyser measurement indicated that treated samples showed significantly decreased in peak viscosity and exhibited a lower tendency towards retrogradation on cooling process compared to untreated TS. Size-exclusion chromatography analysis suggested that the degradation of TS happened during HSJ treatment, and the degradation was more prominent beyond 160 MPa. The results showed that the significant changed in physicochemical and structural properties of treated TS were related to its degradation. These observations would provide an alternative and environmentally approach for starch modification. Image 1 • The viscosity decreased after treated by high speed jet (HSJ). • HSJ treatment significantly improved the solubility of tapioca starch (TS). • HSJ treatment had an effective change in rheological properties of TS. • The degradation of TS happened, and it was more pronounced upon high pressure. [ABSTRACT FROM AUTHOR]

This work addressed to investigate the use of fructose as an additive in the water-based suspension feedstock of a Y-TZP/Al 2 O 3 /SiC multicomponent coating manufactured by suspension plasma spraying. The effect of fructose on suspension rheology and surface tension and on the microstructure and thermal conductivity of the resulting coatings was assessed. It was observed that addition of fructose slightly affected the rheological behaviour of the suspensions while a strong decrease in the surface tension of water occurred. The fructose addition led to the development of columnar-like structures, probably associated with its effect on surface tension. X-ray diffraction patterns in the final coating displayed that crystallinity of tetragonal zirconia formed when fructose was added whereas silicon carbide crystalline phase was practically preserved. The determination of thermal conductivity showed that the formation of a controlled columnar structure along with inter-columnar porosity can be beneficial for thermal insulation. [ABSTRACT FROM AUTHOR]

The yield stress and zeta potential of washed spherical α-Al2O3 suspensions with two to four layers of critic acid(CA) and polyethyleneimine(PEI_Mw1.8and 70 kDa) adsorbed sequentially were characterized. With CA adsorbed as the first layer, pHξ=0 was shifted to a lower pH and the maximum yield stress (τymax) was reduced. With PEI adsorbed as the first layer, the pHξ=0 was moved slightly higher. With the introduction of the second layer, the CA/PEI additive was formed which functioned as a bridging agent. The pH range of yield stress was broadened significantly and increased with the number of layers. This pH ranged from 2.5 to 11. The CA/PEI multilayer additive loses its positive charge at pH >11. There was less adsorption in layer3 and layer4 when lower Mw PEI is applied to the suspension. The CA/PEI multilayer additive formed by PEI of Mw70000 and CA was larger in size than that formed by PEI of Mw 1800 and CA. Lower Mw PEI produced a stronger flocculated network or higher τymax suspension due to a higher concentration of multilayer additive. CA/PEI multilayer additive was participating in bridging and particle bridging interaction was not affected by the adsorption order of CA and PEI.GRAPHICAL ABSTRACT [ABSTRACT FROM AUTHOR]

The mixing of a powder of 10- to 50-μm primary particles into a liquid to form a dispersion with the highest possible solid content is a common industrial operation. Building on recent advances in the rheology of such "granular dispersions," we study a paradigmatic example of such powder incorporation: the conching of chocolate, in which a homogeneous, flowing suspension is prepared from an inhomogeneous mixture of particulates, triglyceride oil, and dispersants. Studying the rheology of a simplified formulation, we find that the input of mechanical energy and staged addition of surfactants combine to effect a considerable shift in the jamming volume fraction of the system, thus increasing the maximum flowable solid content. We discuss the possible microscopic origins of this shift, and suggest that chocolate conching exemplifies a ubiquitous class of powder-liquid mixing. [ABSTRACT FROM AUTHOR]

Abstract A semi-solid flow battery, consisting in a single channel with millimetric width, was operated in flow conditions using Li 4 Ti 5 O 12 (LTO) or LiNi 1/3 Co 1/3 Mn 1/3 O 2 (LNCM) based suspensions versus Li metal. Cell voltages were measured experimentally for various values of charge/discharge current. A model of the electrochemical cell was developed and validated by comparing calculated results with experimental data. The model consists in solving simultaneously the suspension rheology, potential and current within the cell (secondary distribution) and state of charge evolution between the inlet and outlet. Modelling results indicate low pressure drop (<50 kPa), nearly-homogeneous velocity profile along the channel and potential and current gradients in the cell. Comparison of experimental and calculated results indicate that the model takes into account the influence of applied current density on the cell potential but with significant differences on their absolute value, which are discussed in terms of electrochemical stability for the semi-solid suspensions during cycling. Results detailed in this article can, therefore, be applied to larger electrochemical cells or systems based on alternative chemistries, operated in flow conditions. [ABSTRACT FROM AUTHOR]

We study rheology, microstructure, and response to an applied electric field (E) in suspensions of fumed alumina (Al2O3) nanoparticles in a nematic liquid crystal (NLC) made of N-(4-methoxybenzylidene)-4-butylaniline (MBBA). Fumed Al2O3/MBBA suspensions exhibit flowability with nanoparticle volume fraction (ϕ) = 0.001 and 0.007, and become solid-like gels at a nanoparticle ϕ = 0.014 and beyond. The dynamic rheology of gel-like suspensions follows the soft glass rheology (SGR) model. The effective noise temperature remains close to 1 for these Al2O3/MBBA suspensions, which serves as an indication of the presence of glassy dynamics. Further, the optical microscopy and the differential scanning calorimetry (DSC) reveal that the incorporation of fumed Al2O3 nanoparticles causes a significant depression in the nematic-isotropic phase transition temperature (TNI). The gel-like suspensions are less sensitive to pre-shear and show a large structural recovery after shear when compared to Al2O3/silicone oil suspensions. At and above a critical nanoparticle ϕ = 0.005, the suspensions exhibit a reversible nematic-isotropic phase transition under the application of E. [ABSTRACT FROM AUTHOR]

Abstract Solid-liquid separation is carried out in many industries and plays a crucial role in overall process efficiency and product specification. The dewatering characteristics of solid-liquid mixtures, or particulate suspensions, have to be determined to compare filtration equipment performance or to design new equipment. Two theoretical frameworks used to describe solid-liquid separation, and therefore analyse experimental results, are the conventional filtration theory developed by Ruth, Tiller and Shirato and the compressional rheology framework developed by Buscall, White and Landman. In this paper, we compare the characterisation techniques that have developed over time based on these two approaches. This includes a comparison between an air-driven Nutsche Filter, a Compression-Permeability cell and a piston-driven Filtration Rig. The test material is calcium carbonate coagulated by attractive Van der Waals forces at its isoelectric point. We use three different particle sizes, leading to varying degrees of compressibility. The results show good agreement between the two theoretical frameworks for these compressible materials. Overall, this work highlights the differences and similarities between the theories and characterisation techniques alike and gives recommendations for good practice. Graphical abstract Unlabelled Image Highlights • Conventional filtration theory and compressional rheology are interchangeable. • Both frameworks could adopt expertise from each other. • Permeability can be characterised using any device tracking the filtration progress. • Compressibility can just be determined using piston-driven techniques at equilibrium. [ABSTRACT FROM AUTHOR]

Abstract Clay suspensions present complex microstructures in different environments and deep understanding of such microstructures is crucial to control their flow properties. Their rheological profile is closely linked with the structural association (3-D network) of bentonite particles. Nanomaterials are considered very good candidates for smart fluids formulation which can improve the performance of conventional drilling fluids. Their incorporation in water-bentonite suspensions endow complex microstructures and hence complex rheological behavior, which is still under investigation. This study aims to explore the micro-mechanisms involved on shaping this rheological behavior with samples of 7 wt% water-sodium bentonite suspensions containing 0.5 wt% each of, commercial Fe 3 O 4 , commercial SiO 2 NP and custom-made (bare or citric acid coated) Fe 3 O 4 NP at alkaline pH. We tried to achieve this by combining macroscopic measurements (rheological measurements) with microscopic measurements (i.e. TEM). A comprehensive physico-chemical characterization of the materials and suspensions was performed using X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), N 2 adsorption-desorption isotherms and Fourier-transform infrared spectroscopy (FTIR). An effective drying process was adopted using freeze-granulation and freeze-drying (FG-FD) techniques in order to capture as accurately as possible the evolved microstructures of these aqueous bentonite suspensions at the different temperatures (25–60 °C). The results indicated that all samples exhibited a yield stress followed by a shear thinning behavior. The three parameter Herschel-Bulkley model provided excellent fit of the experimental data for all samples. HR-TEM images revealed that the association of the nanoparticles with bentonite particles in different configurations plays a crucial role in their rheological characteristics with the charge and the coating of the added nanoparticles being important factors in determining the magnitude of the effects observed. We hypothesize that attractive magnetic forces between the magnetite nanoparticles may suppress the electrostatic repulsions and thus they may play a key role in promoting the observed aggregation of the nanoparticles which in turn plausibly affected their rheological profile. A thorough examination and understanding of the evolution of such complex inter-particle structures may lead towards an optimal rheology control of such suspensions in a wide range of applications. Graphical abstract Image 1 Highlights • Yield stress of the 7%wt aqueous bentonite suspensions increased upon addition of 0.5 %wt of all types of Fe 3 O 4 NP. • Addition of SiO 2 NP caused the formation of weaker structures and lower yield stress values compared to the base fluid. • The association of the nanoparticles with bentonite particles plays a crucial role in their rheological characteristics. • The charge and nature of the nanoparticles are important factors that determine the evolving microstructural networks. • A model of interactions evolving in water Na+-bentonite suspensions containing different nanoparticles was proposed. [ABSTRACT FROM AUTHOR]

Abstract: The study concerns the development of rheological properties of aqueous TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl)-oxidized nanofibrillated cellulose (NFC) suspensions prepared from a commercially available TEMPO-NFC powder. Ageing of hydrogels with concentrations from 1 to 3 wt% of TEMPO-NFC was investigated by monitoring shear flow and linear viscoelastic properties after different days from sample preparation. For quantitative representation of the results time dependencies of zero shear viscosity and storage modulus are given. The increase of rheological parameters is described by a sigmoidal mathematical model. By superposition of individual data sets master curves displaying reduced values of the most significant parameters are constructed, showing the effect of ageing kinetics. The reduced storage modulus and zero-shear viscosity values increase for 2 and 3 decades, respectively, before reaching final values. Obtained results are useful for several applications of nanocellulose hydrogels, especially for those, where pumping, mixing, coating or injecting is necessary. For example, in biomedical field, a less viscous suspension can be injected to the spot of interest, where the final gel properties are developed.Graphical abstract: [ABSTRACT FROM AUTHOR]

Abstract The zeta (ζ) potential of moderately concentrated (at 15 vol%) boron carbide (B 4 C) suspensions were characterised using electroacoustic spectroscopy. This technique has been validated for use in this application by correlating the ζ-potential to the suspension viscosity (at 30 vol%) across a range of pH values. Zeta potential has been shown to be effective in determining differences in B 4 C powders, reported to be nominally of the same specification in terms of particle size distribution and X-ray diffraction data. The isoelectric (IEP) points for three different as-received B 4 C powders were found to be 4, 7 and less than 2.5. The study showed that differences in ζ-potential across the powders can be minimised via heat treatment, which produced suspensions all with an IEP below 2.5. The study also established the effect of an anionic and a cationic dispersant on ζ-potential and rheology, demonstrating that excess dispersant from a ζ-potential perspective was required to obtain the lowest viscosity. The study concluded that as-received B 4 C powders most likely contain contaminants of a cationic nature and that electroacoustic spectroscopy is a useful tool in determining their behaviour in aqueous suspensions. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Polysaccharide nanocrystals (chitin, cellulose) extracted from biomass are increasingly considered as templates to produce hierarchical anisotropic features in inorganic phases. The organization of nanostructured solids obtained after sol-gel processing results from the complex combination of van der Waals and electrostatic interactions as well as excluded volume effects. Here, we investigate the rheological behavior of colloidal suspensions of chitin nanorods and siloxane oligomers in ethanol. The effects of solvothermal treatments and hydrophobized oligomers were also studied to decipher the respective role of inter-particle colloidal interactions. We demonstrate that interactions between chitin nanorods are strongly affected by the presence of siloxane oligomers. In agreement with previous works, the rheological data confirm the association of the small colloidal siloxane oligomers with the chitin surface. This knowledge is key information to further control the localization of functions in the resulting materials (nanocomposites, catalysts). [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract We examined the dependence of the rheology of capillary suspensions on particle wettability using model ternary liquid/liquid/particle mixtures. Experiments were conducted using silica particles suspended in a majority liquid phase, to which a small minority of a second liquid was added. Silane modification was used to realize three different particle wettabilities ranging from particles being fully-wettable by the minority fluid, to being almost completely non-wettable by the minority liquid. In all three cases, the ternary suspensions showed solid-like behavior, with the yield stress and modulus decreasing as particles became less wettable towards the minority fluid. In all three cases, the minority liquid was found to induce particle aggregation into percolating networks which are responsible for the solid-like rheology. Our results suggest two reasons why the solid-like properties of such suspensions diminish as the particles become less wetting by the minority fluid: because particle network relies on multi-particle capillary clusters (rather than pair-wise meniscus binding), and because a certain fraction of particles become too non-wettable to participate in the network. [ABSTRACT FROM AUTHOR]

Nonequilibrium Brownian dynamics simulations are used to study the effect of polydispersity on the thermodynamics, rheology, microstructure, and shear-induced disorder–order transition in suspensions of charged colloids. Approximately 43 000 particles with 2000 different components of a discretized Schulz distribution at polydispersities from 0% to 30% are simulated on a massively parallel computer. Recent advances in the integral equation theory for polydisperse suspensions are tested and verified with respect to both structure and equilibrium mechanical properties. The low shear rate rheology for both monodisperse and polydisperse suspensions is found to be well represented by the Ree–Eyring model. At higher shear rates an ordered ‘‘string’’ phase is shear induced for low polydispersities (<10%). Increasing the polydispersity further (>=20%) inhibits the ordering, suggesting the existence of a critical polydispersity beyond which a colloidal suspension cannot be induced into an ordered state by shearing. The validity of a generalized, nonequilibrium Stokes–Einstein relationship for polydisperse colloids is also investigated. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Low shear (γ=1 s-1) and shear rate dependent (1 s-1<γ<100 s-1) viscosity measurements on aqueous suspensions of rodlike FD-virus particles (length=880 nm, diameter=9 nm) below and above the overlap concentration c* =1 particle/length3 are presented. Properties like intrinsic viscosity [η], the virus concentration and shear rate dependence of η are studied in deionized (‘‘saltfree’’) suspensions and in the presence of NaCl, where the Coulomb interaction between the particles is totally screened. In the latter case, [η] is in excellent agreement with theoretical predictions [A. R. Altenberger and J. S. Dahler, Macromolecules 18, 1700 (1985); R. M. Davis and W. B. Russel, Macromolecules 20, 518 (1987)]. As a function of the virus concentration, η follows certain power laws in c. The observed exponents depend here on the applied shear rate. In the low shear region, η(c) can be described by the well known Huggins behavior. An attempt to fit the data by the popular stretched exponential form failed. The variation of η with shear rate is compared with available theories [M. Doi and S. F. Edwards, The Theory of Polymer Dynamics (Clarendon, Oxford, 1986); A. R. Altenberger and J. S. Dahler, Macromolecules 18, 1700 (1985); J. S. Dahler, S. Fesciyan, and N. Xystris, Macromolecules 16, 1673 (1983)]. A theory of Hess [Z. Naturforsch. Teil A 35, 915 (1980)] allows us to evaluate the concentration dependent values of the rotational diffusion constant Drot from the η(γ) data which are found to be in very good agreement with the values of Drot, obtained by electric or magnetic birefringence [H. Kramer, M. Deggelmann, C. Graf, M. Hagenbüchle, C. Johner, and R. Weber, Macromolecules 25, 4325 (1992); J. F. Maguire and J. P. McTague, Phys. Rev. Lett. 45, 1891 (1980); H. Nakamura and K. Okano, Phys. Rev. Lett. 50, 186 (1983)]. For strong Coulomb interaction among the suspended viruses no adequate... [ABSTRACT FROM AUTHOR]

Presents a study that characterized the kinetics of structure formation in electrorheological suspensions by the time required to form percolating fibers following application of an external electric field. Experimental details; Results of the study; Conclusion.

Stimuli responsive viscosity modifiers entail an important class of materials which allow for smart material formation utilizing various stimuli for switching such as pH, temperature, light and salinity. They have seen applications in the biomedical space including tissue engineering and drug delivery, wherein stimuli responsive hydrogels and polymeric vessels have been extensively applied. Applications have also been seen in other domains like the energy sector and automobile industry, in technologies such as enhanced oil recovery. The chemistry and microstructural arrangements of the aqueous morphologies of dissolved materials are usually sensitive to the aforementioned stimuli which subsequently results in rheological sensitivity as well. Herein, we overview different structures capable of viscosity modification as well as go over the rheological theory associated with classical systems studied in literature. A detailed analysis allows us to explore correlations between commonly discussed models such as molecular packing parameter, tube reptation and stress relaxation with structural and rheological changes. We then present five primary mechanisms corresponding to stimuli responsive viscosity modification: (i) packing parameter modification via functional group conditioning and (ii) via dynamic bond formation, (iii) mesh formation by interlinking of network nodes, (iv) viscosity modification by chain conformation changes and (v) viscosity modification by particle jamming. We also overview several recent examples from literature that employ the concepts discussed to create novel classes of intriguing stimuli responsive structures and their corresponding rheological properties. Furthermore, we also explore systems that are responsive to multiple stimuli which can provide enhanced functionality and versatility by providing multi-level and precise actuation. Such systems have been used for programmed site-specific drug delivery. [Display omitted] • The chemistry of aqueous suspensions is correlated to the rheological properties. • Modulation of the viscosity can occur via application of various stimuli. • The rheological changes can be reversible or irreversible depending on system specifics. • Five primary mechanisms that explain viscosity modification have been identified. • Multiple-stimuli responsive systems with enhanced functionality are discussed. [ABSTRACT FROM AUTHOR]

Rheological properties of starch are affected by swelling of the granules that is in turn controlled by the degree of crosslinking. A previously developed model for swelling of starch granules was extended to account for electrostatic interactions. Maize starch was crosslinked with sodium trimetaphosphate. Granule swelling of 8% suspension of crosslinked maize starch when subjected to heating to 70,75,80,85 and 90 °C was more pronounced at higher temperatures eventually approaching equilibrium with the swelling ratio decreasing with increase in extent of crosslink. The number of crosslinks in the starch network was inferred from equilibrium swelling and related to peak viscosity and zeta potential. Chemical potential profile as well as the temperature profile within the granule at different times were predicted which were then employed to evaluate the evolution of granule size. The proposed model is able to describe the effect of crosslinking on swelling behavior. [ABSTRACT FROM AUTHOR]

Suspensions are composed of mixtures of particles and fluid and are omnipresent in natural phenomena and in industrial processes. The present paper addresses the rheology of concentrated suspensions of non-colloidal particles. While hydrodynamic interactions or lubrication forces between the particles are important in the dilute regime, they become of lesser significance when the concentration is increased, and direct particle contacts become dominant in the rheological response of concentrated suspensions, particularly those close to the maximum volume fraction where the suspension ceases to flow. The rheology of these dense suspensions can be approached via a diversity of approaches that the paper introduces successively. The mixture of particles and fluid can be seen as a fluid with effective rheological properties but also as a two-phase system wherein the fluid and particles can experience relative motion. Rheometry can be undertaken at an imposed volume fraction but also at imposed values of particle normal stress, which is particularly suited to yield examination of the rheology close to the jamming transition. The response of suspensions to unsteady or transient flows provides access to different features of the suspension rheology. Finally, beyond the problem of suspension of rigid, non-colloidal spheres in a Newtonian fluid, there are a great variety of complex mixtures of particles and fluid that remain relatively unexplored. [ABSTRACT FROM AUTHOR]