Rheology Of Suspensions Research Articles

Microstructure and rheology of shear thickening colloidal suspensions under transient flows

Novel measurements of the spatiotemporal microstructure of a continuous shear thickening colloidal suspension under shear cessation and reversal using small angle neutron scattering in a 1–2 shear cell are presented for moderate to high Péclet numbers. In the shear cessation experiments from high Péclet shear flow, two-step relaxation mechanism is found. Particles first readily diffuse on a characteristic timescale of single particle Brownian motion, followed by slower relaxation dynamics on a timescale of short-time self-diffusion when caging effects start dominating. In the shear reversal experiment, the unchanged scattering intensity and the quick flip in anisotropic structure around the shear thickened state suggest the persistence of hydroclusters without transitioning through the equilibrium structure, at least in a time resolution of 0.01 s. Access to the time evolution of microstructure provides valuable insights into the spatiotemporal details of interparticle interactions governing colloidal suspension rheology, such as Brownian, hydrodynamic, and nanotribological forces.

Insight into the Viscoelasticity of Self-Assembling Smectic Liquid Crystals of Colloidal Rods from Active Microrheology Simulations.

The rheology of colloidal suspensions is of utmost importance in a wide variety of interdisciplinary applications in formulation technology, determining equally interesting questions in fundamental science. This is especially intriguing when colloids exhibit a degree of long-range positional or orientational ordering, as in liquid crystals (LCs) of elongated particles. Along with standard methods, microrheology (MR) has emerged in recent years as a tool to assess the mechanical properties of materials at the microscopic level. In particular, by active MR one can infer the viscoelastic response of a soft material from the dynamics of a tracer particle being dragged through it by external forces. Although considerable efforts have been made to study the diffusion of guest particles in LCs, little is known about the combined effect of tracer size and directionality of the dragging force on the system's viscoelastic response. By dynamic Monte Carlo simulations, we apply active MR to investigate the viscoelasticity of self-assembling smectic (Sm) LCs consisting of rodlike particles. In particular, we track the motion of a spherical tracer whose size is varied within a range of values matching the system's characteristic length scales and being dragged by constant forces that are parallel, perpendicular, or at 45° to the nematic director. Our results reveal a uniform value of the effective friction coefficient as probed by the tracer at small and large forces, whereas a nonlinear, force-thinning regime is observed at intermediate forces. However, at relatively weak forces the effective friction is strongly determined by correlations between the tracer size and the structure of the host fluid. Moreover, we also show that external forces forming an angle with the nematic director provide additional details that cannot be simply inferred from the mere analysis of parallel and perpendicular forces. Our results highlight the fundamental interplay between tracer size and force direction in assessing the MR of Sm LC fluids.

Rheology of dense fiber suspensions: Origin of yield stress, shear thinning, and normal stress differences

Rheology of dense fiber suspensions: Origin of yield stress, shear thinning, and normal stress differences

Rheology of non-Brownian suspensions: a rough contact story

Rheology of non-Brownian suspensions: a rough contact story

Control of mush complex viscosity on mid-ocean ridge topography: A fluid–structure model analysis

This article exploits the interaction dynamics of the elastic oceanic crust with the underlying mush complexes (MC) to constrain the axial topography of mid-ocean ridges (MORs). The effective viscosity (μeff) of MC beneath MORs is recognized as the crucial factor in modulating their axial high vs flat topography. Based on a two-step viscosity calculation (suspension and solid-melt mixture rheology), we provide a theoretical estimate of μeff as a function of melt suspension characteristics (crystal content, polymodality, polydispersity, and strain rate) and its volume fraction in the MC region. We then develop a numerical model to show the control of μeff on the axial topography. Using an enthalpy-porosity-based fluid formulation of uppermost mantle, the model implements a one-way fluid–structure interaction that transmits viscous forces of the MC region to the overlying upper crust. The limiting non-rifted topographic elevations (−0.06–1.27 km) of model MORs are found to occur in the viscosity range of μeff = 1012–1014 Pa s. The higher end (1013–1014) Pa s of this spectrum produces axial highs, which are replaced by flat or slightly negative topography as μeff≤5×1012 Pa s. We discuss a number of major natural MORs to validate the model findings.

Microscopically grounded constitutive model for dense suspensions of soft particles below jamming

Materials made up of soft elastic particles suspended in a fluid form a broad subset of complex fluids, including emulsions, suspensions of microgels, liposomes, or vesicles. Until now, no established model can describe how they flow. Here, we derive from particle-level dynamics a constitutive model describing the rheology of two-dimensional dense soft suspensions below the jamming transition, in a regime where elastic interactions dominate the stress response. Our model successfully captures many observed rheological features, such as shear thinning, normal stresses, and normal stress differences scaling respectively linearly and quadratically with deformation rate in the slow flow limit.

Effect of DLVO interactions on the rheology and microstructure of non-Brownian suspensions

Effect of DLVO interactions on the rheology and microstructure of non-Brownian suspensions

Enhancing the flowability of limestone water suspension for economical transportation by variation in particle size distribution

Hydrotransport is increasingly a popular technology due to its low specific energy consumption and nonpolluting nature. The current work presents a thorough characterization of a limestone sample to explore the influence of blending medium and coarse particles with fine particulate slurry on the rheology, slurryability, and stability of a limestone water suspension. Various bench-scale studies are performed to identify the physicochemical, morphological, and flow features of limestone samples. Eight separate bi-modal slurry samples are prepared using limestone materials with three unique particle size ranges (53, 53–75, and 75–106 µm). The rheological properties of the slurry are tested at shear rates ranging from 50 to 500 1/s, and regression analysis is used to determine the nature of the slurry. The solid concentration of the suspension sample ranges between 10 and 70% with a flow velocity range of 0.25–1.5 m/s through a 100 mm diameter pipeline. Finally, essential criteria such as apparent viscosity, settling properties, pressure drop, and specific energy consumption are used to determine the optimal particle size distribution. The ideal proportion of medium particles (53–75 µm) mixing in the fine particulate slurry suspension is 40%, while the fraction of coarse particles (75–106 µm) is 30% (by weight).

Impact of physico‐chemical properties of nanocellulose on rheology of aqueous suspensions and its utility in multiple fields: A review

AbstractNanocellulose (NC), due to its sustainable nature, high aspect ratio, superior mechanical strength, and availability of functionalizable OH groups, has been widely utilized as reinforcement in numerous fluids/plastics. The physico‐chemical properties of NC, like surface characteristics, dimensions/aspect ratio and their concentration, significantly impact the interparticle interactions, such as the extent of hydrogen bonding, van derWaalforces, hydrophobicity, electrostatic attraction/repulsion, and cellulose entanglement, and have been found to play a critical role in regulating the overall rheological characteristics of fluids. The functionalized NC aqueous suspension exhibited unique shear thinning properties, thixotropic behavior, and quick steady‐state viscosity recovery and viscoelastic properties. However, upon adding functionalized NC to other fluids, a different impact was noticed. For instance, it improved the viscosity, G′ and mechanical stability of bio‐ink; the setting time and mechanical strength of cementitious fluids; increased the filtration performance and provided a unique thermo‐thickening impact in case of water‐based drilling‐fluid; enhanced viscosity with time and heat in case of oil recovery, and so forth. Keeping in view the notable dependence of the rheology of fluids on NC additives, in the present review article, the impact of various physico‐chemical properties of NC additives on the rheological behavior of NC aqueous suspension and its utility as a rheology modifier in multiple advanced fields has been explored. This review article, compared to previous studies, warrants an update on the impact of recent NC surface functionalization/blending techniques employed and NC aspect ratio on specific properties of multiple advanced fluids.

Shear rheology of a dilute suspension of thin rings

The rheology of suspensions of rings (tori) rotating in an unbounded low Reynolds number simple shear flow is calculated using numerical simulations at dilute particle number densities ( n ≪ 1 ). Suspensions of non-Brownian rings are studied by computing pair interactions that include hydrodynamic interactions modeled using slender body theory and particle collisions modeled using a short-range repulsive force. Particle contact and hydrodynamic interactions were found to have comparable influences on the steady-state Jeffery orbit distribution. The average tilt of the ring away from the flow-vorticity plane increased during pairwise interactions compared to the tilt associated with Jeffery rotation and the steady-state orbit distribution. Particle stresses associated with the increased tilt during the interaction were found to be comparable to the stresses induced directly by particle contact forces and the hydrodynamic velocity disturbances of other particles. The hydrodynamic diffusivity coefficients in the gradient and vorticity directions were also obtained and were found to be two orders of magnitude larger than the corresponding values in fiber suspensions at the same particle concentrations. Rotary Brownian dynamics simulations of isolated Brownian rings were used to understand the shear rate dependence of suspension rheology. The orbit distribution observed in the regime of weak Brownian motion, P e ≫ ϕ T − 3, was surprisingly similar to that obtained from pairwise interaction calculations of non-Brownian rings. Here, the Peclet number P e is the ratio of the shear rate and the rotary diffusivity of the particle and ϕ T is the effective inverse-aspect ratio of the particle (approximately equal to 2 π times the inverse of its non-dimensional Jeffery time period). Thus, the rheology results obtained from pairwise interactions should retain accuracy even for weakly Brownian rings ( n ≪ 1 and ϕ T − 3 ≪ P e ).

Electric and magnetic field-responsive suspension rheology of core/shell-shaped iron oxide/polyindole microspheres

Electric and magnetic field-responsive suspension rheology of core/shell-shaped iron oxide/polyindole microspheres

Rheology of concentrated fiber suspensions with a load-dependent friction coefficient

We numerically investigate the rheology of concentrated suspensions of fibers by modeling them as continuous slender bodies suspended in an incompressible fluid, including surface roughness. We model contact dynamics and friction in the suspension using a normal load-dependent friction coefficient and investigate the shear rate-dependent rheology of suspensions for different aspect ratios, volume fractions, roughness, and flexibility values.

Steady-state extensional rheology of a dilute suspension of spheres in a dilute polymer solution

It is well-known and intuitive that addition of a dilute volume concentration of spheres increases the viscosity of a Newtonian liquid. We find that a viscoelastic liquid undergoing uniaxial extensional flow at small $D\phantom{\rule{0}{0ex}}e$ (extension rate times the polymer relaxation time) experiences a larger increase in viscosity than the Newtonian case due to wakes of extra polymer stretch produced downstream of the spheres. However, when $D\phantom{\rule{0}{0ex}}e\ensuremath{\gtrsim}0.6$, the highly stretched polymer in the bulk fluid collapses near the particle surface and the suspension deforms more easily than the particle-free viscoelastic fluid.

Influence of resin composition on rheology and polymerization kinetics of alumina ceramic suspensions for digital light processing (DLP) additive manufacturing

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.

Rheology of Dense Suspensions under Shear Rotation.

Dense non-Brownian suspensions exhibit a spectacular and abrupt drop in viscosity under change of shear direction, as revealed by shear inversions (reversals) or orthogonal superposition. Here, we introduce an experimental setup to systematically explore their response to shear rotations, where one suddenly rotates the principal axes of shear by an angle θ, and measure the shear stresses with a biaxial force sensor. Our measurements confirm the genericness of the transient decrease of the resistance to shear under unsteady conditions. Moreover, the orthogonal shear stress, which vanishes in steady state, takes non-negligible values with a rich θ dependence, changing qualitatively with solid volume fraction ϕ and resulting in a force that tends to reduce or enhance the direction of flow for small or large ϕ. These experimental findings are confirmed and rationalized by particle-based numerical simulations and a recently proposed constitutive model. We show that the rotation angle dependence of the orthogonal stress results from a ϕ-dependent interplay between hydrodynamic and contact stresses.

Effect of polydispersity and bubble clustering on the steady shear viscosity of semidilute bubble suspensions in Newtonian media

In this work, we examine the steady shear rheology of semidilute polydisperse bubble suspensions to elucidate the role of polydispersity on the viscosity of these systems. We prove theoretically that the effect of polydispersity on suspension viscosity becomes apparent only if the bubble size distribution is bimodal, with very small and very large bubbles having similar volume fractions. In any other case, we can consider the polydisperse suspension as monodisperse, with the average bubble diameter equal to the De Brouckere mean diameter (d43). To confirm the theoretical results, we carried out steady shear rheological tests. Our measurements revealed an unexpected double power-law decay of the suspension relative viscosity at average capillary numbers between 0.01 and 1. To investigate this behavior further, we visualized the produced bubble suspensions under shear. The visualization experiments revealed that bubbles started forming clusters and threads at an average capillary number around 0.01, where we observed the first decay of viscosity. Clustering and alignment have been associated with shear-thinning behavior in particle suspensions. We believe that the same holds for bubble suspensions, where bubble clusters and threads align with the imposed shear flow, reducing the streamline distortions and, in turn, resulting in a decrease in the suspension viscosity. Consequently, we can attribute the first decay of the relative viscosity to the formation of bubble clusters and threads, proving that the novel shear-thinning behavior we observed is due to a combination of bubble clustering and deformation.

Capillary-Stress Controlled Rheometer Reveals the Dual Rheology of Shear-Thickening Suspensions

The rheology of dense colloidal suspensions, which may undergo discontinuous shear thickening or shear jamming, is particularly difficult to analyze with conventional rheometers. Here, we develop a rheometer adapted to colloidal suspensions: the “capillarytron,” which uses the air-suspension capillary interface to impose particle (or osmotic) pressure during shear. The main virtues of this new device are that (i) it gives direct access to the suspension friction coefficient, (ii) it operates for very dense suspensions up to jamming, and, most importantly, (iii) it decouples the stresses developed within the suspension from the applied shear rate. We can, thus, smoothly move through the different frictional states of the system, precisely in the range of volume fractions where discontinuous shear thickening or shear jamming occur under volume-imposed conditions. Our results obtained with the capillarytron provide the first complete characterization of the dual frictional behavior of a model shear-thickening suspension, in agreement with the recently proposed frictional transition scenario. Based on a new concept in rheometry, the capillarytron unlocks the path to pressure-imposed rheology on colloidal and Brownian suspensions. Moreover, its fine control of the particle pressure via the soft capillary interface opens the possibility to explore the flow of “fragile” particles close to jamming, such as Brownian colloids, active particles, and living cells.Received 18 November 2022Revised 15 December 2022Accepted 9 January 2023DOI:https://doi.org/10.1103/PhysRevX.13.011024Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasJammingNon-Newtonian fluidsRheologyPhysical SystemsComplex fluidsGranular fluidsPolymers & Soft Matter

Analysis of the rheology of magnetic bidisperse suspensions in the regime of discontinuous shear thickening

Analysis of the rheology of magnetic bidisperse suspensions in the regime of discontinuous shear thickening

Microscopic activated dynamics theory of the shear rheology and stress overshoot in ultradense glass-forming fluids and colloidal suspensions

We formulate a particle and force level, activated dynamics-based statistical mechanical theory for the continuous startup nonlinear shear rheology of ultradense glass-forming hard sphere fluids and colloidal suspensions in the context of the elastically collective nonlinear Langevin equation approach and a generalized Maxwell model constitutive equation. Activated structural relaxation is described as a coupled local-nonlocal event involving caging and longer range collective elasticity which controls the characteristic stress relaxation time. Theoretical predictions for the deformation-induced enhancement of mobility, the onset of relaxation acceleration at remarkably low values of stress, strain, or shear rate, apparent power law thinning of the steady-state structural relaxation time and viscosity, a nonvanishing activation barrier in the shear thinning regime, an apparent Herschel–Buckley form of the shear rate dependence of the steady-state shear stress, exponential growth of different measures of a yield or flow stress with packing fraction, and reduced fragility and dynamic heterogeneity under deformation were previously shown to be in good agreement with experiments. The central new question we address here is the defining feature of the transient response—the stress overshoot. In contrast to the steady-state flow regime, understanding the transient response requires an explicit treatment of the coupled nonequilibrium evolution of structure, elastic modulus, and stress relaxation time. We formulate a new quantitative model for this aspect in a physically motivated and computationally tractable manner. Theoretical predictions for the stress overshoot are shown to be in good agreement with experimental observations in the metastable ultradense regime of hard sphere colloidal suspensions as a function of shear rate and packing fraction, and accounting for deformation-assisted activated motion appears to be crucial for both the transient and steady-state responses.

Tribological variable-friction coefficient models for the simulation of dense suspensions of rough polydisperse particles

The rheology of concentrated suspensions of particles is complex and typically exhibits a shear-thickening behavior in the case of repulsive interactions. Despite the recent interest arisen, the causes of the shear-thickening remain unclear. Frictional contacts have been able to explain the discontinuous shear thickening in simulations. However, the interparticle friction coefficient is considered to be constant in most simulations and theoretical works reported to date despite the fact that tribological experiments demonstrate that the friction coefficient can not only be constant (boundary regime) but also decrease (mixed regime) or even increase (full-film lubrication regime), depending on the normal force and the relative velocity between the particles and the interstitial liquid between them. Interestingly, the transition between the boundary regime and the full-lubrication regime is governed by the particle average roughness. Particle-level simulations of suspensions of hard spheres were carried out using short-range lubrication and roughness-dependent frictional forces describing the full Stribeck curve. Suspensions with different particle’s roughness were simulated to show that the particle roughness is a key factor in the shear-thickening behavior; for sufficiently rough particles, the suspension exhibits a remarkable shear-thickening, while for sufficiently smooth particles, the discontinuous shear-thickening disappears.