Journal of Rheology, Volume 65, Issue 2, Page 289-289, March 2021.

Brownian dynamics simulations were employed to investigate the rheological properties and structure of suspensions of rigid spherocylinders, as a model for rodlike colloids. The spherocylinders interacted only through a soft repulsive force that mimicked a hard spherocylinder interaction. The translational and rotational diffusivities of hard spherocylinder suspensions were reproduced. Liquid crystalline

The effects of apparent wall slip on rheometric measurements of waxy gels are quantified for gels consisting of a macrocrystalline wax added in mineral oil in concentrations of 3.0 and 7.5 wt. %. The waxy gels are formed in situ in a stress-controlled rheometer, and rheological properties are then obtained. Seven different geometry configurations, including parallel plates, concentric cylinders, and

The rheology and microstructure of soft particle glasses during startup flow are studied using three-dimensional particle dynamics simulations at different particle volume fractions and shear rates. The behavior of transient stress depends on the applied shear rate. At high shear rates, soft particle glasses exhibit a static yield stress signaled by a stress overshoot followed by a relaxation to a

The yield stress behavior of colloidal gels with embedded active particles is studied with three experiments: start-up of steady shear, oscillatory strain amplitude sweep, and creep testing. Activity is generated by Janus particles with a platinum hemisphere; these particles undergo self-diffusiophoretic and self-electrophoretic motion in hydrogen peroxide solutions. The free particle active motion

In some recent experiments on entangled polymers of stress growth in the startup of fast shear flows, an undershoot in the shear stress is observed following the overshoot, i.e., before approaching the steady state. Whereas tumbling of the entangled chain was proposed to be at its origin, here, we investigate another possible cause for the stress undershoot, i.e., slippage at the interface between

We simulate a dense athermal suspension of soft particles sheared between hard walls of a prescribed roughness profile, fully accounting for the fluid mechanics of the solvent between the particles and for the solid mechanics of changes in the particle shapes. We, thus, capture the widely observed rheological phenomenon of wall slip. For imposed stresses below the material’s bulk yield stress, we show

In this work, we introduce a comprehensive machine-learning algorithm, namely, a multifidelity neural network (MFNN) architecture for data-driven constitutive metamodeling of complex fluids. The physics-based neural networks developed here are informed by the underlying rheological constitutive models through the synthetic generation of low-fidelity model-based data points. The performance of these

Viscosity and phase transitions were studied in the (KF-KCl)eut.-(10 mol. %)K2SiF6 system. Synchronous thermal analysis (STA) was used to study the phase transformations in the system in the temperature range of 298–1113 K. The (KF-KCl)eut.-(10 mol. %)K2SiF6 melt was found to be homogeneous at 903–993 K. The viscosity of the system under study was investigated by the rotational viscometer FRS 1600

We study buffered aqueous solutions of deoxyribonucleic acid isolated from bacteriophage lambda (λ-DNA) at shear rates up to 105 s−1. The shear rates are accessed with a narrow-gap rheometer at gap widths down to 20 μm. At lower shear rates, our data merge with the literature values. At high shear rates, the viscosity levels off into an infinite-shear viscosity plateau. Hence, the viscosity functions

Scientific questions surrounding the shear-dependent microstructure of carbon black suspensions are motivated by a desire to predict and control complex rheological and electrical properties encountered under shear. In this work, direct structural measurements over a hierarchy of length scales spanning from nanometers to tens of micrometers are used to determine the microstructural origin of the suspension

Recent studies have shown that rheological material functions that can be linked to structural measures are defined in terms of the recoverable and unrecoverable strains [for example, Lee et al., Phys. Rev. Lett. 122, 248003 (2019)]. In this study, we explore the consequences of applying these ideas to transient nonlinear rheological tests, using new material functions including an elastic modulus

A semi-empirical constitutive equation is suggested for the model comb polymer with the purpose to simultaneously describe the intrinsic medium amplitude oscillatory shear (MAOS) behaviors and transient behaviors in start-up elongational experiments. The molecular stress and hierarchical relaxation of comb polymers are discussed on the basis of the orientation-stretch coupled conformation tensor of

The paraffin molecules in crude oil crystalize and precipitate out as the oil cools, resulting in a sharp increase in oil viscosity and further the gelation of the oil. The waxy crude oil gel exhibits complex rheological behaviors, such as viscoelasticity, yield stress, and thixotropy, posing challenges to the flow assurance of pipelines. Previous studies have verified that applying a high-voltage

The linear viscoelasticity of coacervates formed by oppositely charged polyelectrolytes in the salt solution is reviewed, with a focus on time-temperature, time-salt, time-pH, and time-hydration superpositions, and on fundamental relaxation mechanisms. A variety of polyelectrolyte pairs are covered, showing the frequent, but not universal, success of the time-salt superposition. Master curves in many

Journal of Rheology, Volume 65, Issue 1, Page 75-75, January 2021.

Journal of Rheology, Volume 65, Issue 1, Page 73-73, January 2021.

We show that the average length ⟨ L ⟩ of threadlike micelles in surfactant solutions predicted by fitting results of a mesoscopic simulation, the “pointer algorithm,” to experimental G′(ω), G″(ω) data, is longer than, and more accurate than, that from a scaling law that equates ⟨ L ⟩ / l e to the modulus ratio G 0 / G m i n ′ ′. Here, G0 is the plateau modulus, G m i n ′ ′ is obtained at the local

We develop a method for efficient prediction of linear and nonlinear rheology of polydisperse polymers by judicious selection of a small number of representative polymer molecules from the large ensemble of chains comprising the molecular weight and branching distribution. Specifically, we use a numerical inversion of the double reptation model to select five or six representative molecular species

The nozzle pressure was monitored in a fused filament fabrication process for the printing of high impact polystyrene. The contact pressure, defined as the pressure applied by the newly deposited layer onto the previous layer, is experimentally calculated as the difference between the pressure during printing and open discharge at the same volumetric flow rates. An analytical method for estimating

The rheological behaviors of suspension of ideally conductive particles in an electric field are studied using large-scale numerical simulations in the limit of the zero-shear-rate flow. Under the action of an electric field, the particles undergo the nonlinear electrokinetic phenomenon termed dipolophoresis, which is the combination of dielectrophoresis and induced-charge electrophoresis. For ideally

We found an anomalous nonlinear behavior under large amplitude oscillatory shears, where the amplitude stress deviates strongly from the linear dependence of strain, while the time dependence of stress remains sinusoidal. This phenomenon is usually accompanied with the Payne effect of filled rubbers. In order to understand the molecular details regarding this unusual behavior, we examined a series

Journal of Rheology, Volume 64, Issue 6, Page 1501-1524, November 2020.

Journal of Rheology, Volume 64, Issue 6, Page 1497-1499, November 2020.

We present a new strategy for introducing population balances into full-chain constitutive models of living polymers with linear chain architectures. We provide equations to describe a range of stress relaxation processes covering both unentangled systems (Rouse-like motion) and well-entangled systems (reptation, contour length fluctuations, chain retraction, and constraint release). Special attention

The effects of temperature, pressure, and supercritical carbon dioxide (scCO2) concentration are investigated on the rheological behavior of poly(methyl methacrylate)/expanded graphite (PMMA/EG) composites with 1, 4, and 7 wt. % EG. The validity of the time-temperature superposition and time-pressure-scCO2 concentration superposition principles for the PMMA/EG composites is explored. At atmospheric

Rheological models based on fractional order derivatives have been applied to characterize the linear viscoelasticity of asphalt cements for a long time. Such models provide continuous spectra which are fundamentally related to the molecular characteristics and facilitate analytical investigations as compared to discrete representations. With the increasing complexity in asphalt composition to satisfy

Filled vulcanizates exhibit the nonlinear Payne effect under dynamic deformations at high strain amplitudes, while the underlining mechanisms are still in dispute. Herein, polydimethylsiloxane (PDMS) networks are prepared via end-linking of α,ω-vinyl-terminated PDMS chains by the thiol-ene reaction, and the influences of silica on the dynamic rheological responses are investigated. The presence of

We derive new analytical solutions for the nonaffine Johnson–Segalman/Gordon–Schowalter (JS/GS) constitutive equation with a general relaxation kernel in medium-amplitude oscillatory shear (MAOS) deformation. The results show time-strain separable (TSS) nonlinearity, therefore providing new physically meaningful interpretation to the heuristic TSS nonlinear parameter in MAOS [Martinetti and Ewoldt

In light of recent advancements in the constitutive modeling of bidisperse and polydisperse entangled linear polymers, we present a new “multifluid” generalization of the classic two-fluid approximation for flows of inhomogeneous polymer blends. As an application of the model, we consider predictions for the linear and nonlinear dynamics of shear induced demixing (SID) instabilities in blends with

Polymer crystallization occurs in many plastic manufacturing processes, from injection molding to film blowing. Linear low-density polyethylene (LLDPE) is one of the most commonly processed polymers, wherein the type and extent of short-chain branching (SCB) may be varied to influence crystallization. In this work, we report simultaneous measurements of the rheology and Raman spectra, using a Rheo-Raman

The monomer friction coefficient ζ is known to vary with monomer structure, solvent, and concentration; its variation with chain conformation is less well known and appreciated. We explore the decrease of the friction coefficient in the extensional flow of polymer liquids, during which chains become partially stretched and aligned. To induce stretching and alignment similar to the extensional flow

Nanoparticles (NPs) distributed near the interface (in the droplets/matrix) and exactly at the interface are constructed in model polypropylene/polystyrene blends filled with different hydrophobic silica. It is found that the initially refined morphology of blends is stabilized under quiescent annealing by all NPs, especially for NPs exactly at the interface. However, the refined morphology in the

This study sheds light on the effect of nitrogen (N) doping of carbon nanotubes (CNTs) on medium-amplitude oscillatory shear (MAOS) response of CNT/polyvinylidene fluoride (PVDF) nanocomposites within a rheologically percolated concentration regime. Custom-synthesized CNTs without and with nitrogen heteroatom (at a nitrogen atomic percent of 3.85 at. %) were incorporated into a PVDF matrix using a

Thermoplastic vulcanizates (TPVs) are a special class of polymer blends comprised of a thermoplastic polypropylene (PP) matrix and a dynamically vulcanized ethylene propylene diene monomer (EPDM) rubber. Due to the presence of crosslinked rubber particles, TPVs exhibit complex rheological fingerprints similar to those of soft elastic solids. In this study, we attempt to draw a correlation between the

We theoretically study the stress relaxation process of small amounts of entangled ring polymer chains in a linear matrix by combining several important physical mechanisms: (1) Rouse relaxation, (2) longitudinal stress relaxation along the tube, and (3) constraint release. The contribution to stress relaxation of entangled rings by longitudinal modes is calculated analytically, and a compact expression

Conventional polymers used in enhanced oil recovery (EOR) are acrylamide-based copolymers of very high molecular weight. Their viscosity in aqueous solution depends on various physicochemical parameters such as monomer composition, concentration, average molecular weight, polydispersity, salinity level and ionic composition, temperature, etc. Moreover, solutions are non-Newtonian; they exhibit low-shear

An experimental protocol is developed to directly measure the new material functions revealed by medium amplitude parallel superposition (MAPS) rheology. This protocol measures the medium amplitude response of a material to a simple shear deformation composed of three sine waves at different frequencies, revealing a rich dataset consisting of up to 19 measurements of the third-order complex modulus

In this work, we apply lubricated squeezing to perform planar extension of styrene-butadiene rubbers (SBRs) and illustrate how large step-strained SBR undergo chain relaxation. When the imposed step strain is moderate or the stepwise planar extension is imposed sufficiently slowly, the stress relaxation is spatially uniform. Upon a large stepwise extension imposed over a period much shorter than the

We introduce a constitutive model to describe the rheological behavior of gelled waxy crude oil. The irreversible time-dependence effects were experimentally characterized and incorporated into the model. The model is developed with basis on the data of standard rheological tests to determine the parameters of novel material functions that arise in the model development procedure, namely, flow curve

Cohesion forces strongly alter the flow properties of a granular material. To investigate this influence, we focus on a simple configuration: the collapse of a cohesive granular column. To do so, we adopt a numerical approach and implement a peculiar rheology in a Navier–Stokes solver (Basilisk): the so-called μ ( I )-rheology, usually used for dry granular materials, supplemented by a yield stress

A combination of experiments and Brownian Dynamics simulations is utilized to examine the mechanisms of yielding and flow in attractive colloidal glasses during start-up shear flow. In both experiments and simulations, the transient stress exhibits two stress peaks indicative of two-step yielding processes. The first yield depends largely on details of interparticle potential whereas the second yield

Aging soft glassy materials do not follow time-translational invariance and violate the principles of linear viscoelasticity, such as the relation between the dynamic moduli in the frequency domain and the stress relaxation modulus in the time domain. Using an aqueous suspension of hectorite clay, a model aging soft glassy material, we account for time-dependent behavior by transforming the experimentally

Dense suspensions of model hard-sphere (HS)-like colloids, with different particle sizes, are examined experimentally near and in the glass state, under shear and extensional rheology. Under steady shear flow, we detect both continuous and discontinuous shear thickening (DST) above a critical shear rate (or shear stress), depending on the particle size and volume fraction. Start-up shear experiments

We report experiments on spatiotemporal evolution of the velocity profiles in shear-banding wormlike micelles upon inception of the flow in a Taylor–Couette (TC) cell. Both moderately entangled and highly entangled solutions are considered over a broad range of fluid elasticity E. Fluid elasticity, E = Wi/Re, characterizes the relative importance of the elastic to inertial effects. For both moderately

We explore theoretically the interplay between shear banding and edge fracture in complex fluids by performing a detailed simulation study within two constitutive models: the Johnson–Segalman model and the Giesekus model. We consider separately parameter regimes in which the underlying constitutive curve is monotonic and nonmonotonic, such that the bulk flow (in the absence of any edge effects) is

By means of extensive particle dynamics simulations in a three-dimensional model, we analyze the rheology and granular texture in the steady-state of the viscoinertial granular flow. The interactions between dry particles are added by the theoretical description of the capillary cohesion forces and viscous forces due to the presence of the viscous liquid bridge. We show that the rheology of such flow

The nonequilibrium properties of uniformly charged linear polymers in the presence of explicit counterions under shear flow are studied by coarse-grained mesoscale hydrodynamics simulations. The conformational properties of the polyelectrolyte (PE) are quantified by the gyration tensor, the distribution of the end-to-end distance, and alignment with the flow, which display rather universal behavior

In a concentrated suspension, particles come into contact due to the presence of asperities on their surfaces. As a result, the contact forces and interparticle friction become one of the important factors governing the rheology of rigid particle suspensions at high concentrations. We show that a load-dependent friction model can be used to reproduce the experimentally observed shear thickening [ST—continuous

We show how two-species models, already proposed for the rheology of networks of associative polymer solutions, can be derived from nonequilibrium thermodynamics using the generalized bracket formalism. The two species refer to bridges and (temporary) dangling chains, both of which are represented as dumbbells. Creation and destruction of bridges in our model are accommodated self-consistently by assuming

Thermorheological behavior was examined for poly(vinyl alcohol) (PVA) and borax aqueous solutions. The PVA content was fixed to be approximately four times the entanglement concentration, and the borax concentration Cborax was varied in a wide range of 0–10.4 mM. In this system, borate ions yielded from the hydrolysis of borax can crosslink the PVA chains to form a reversible network. At low Cborax = 2

Rheological behavior of nanolayered films of polyethylene/polyamide 6 (PE/PA6) compatibilized in situ during the coextrusion process has been studied at a temperature between the melting temperatures of PE and PA6. Thanks to the high number of interfaces, a drastic increase in dynamic moduli has been measured when increasing the interphase volume fraction in the films, and a solid-like behavior for

In this paper, I present a simple and self-consistent framework based on microrheology that allows one to obtain the mechanical response of viscoelastic fluids and gels from the motion of probe particles immersed on it. By considering a non-Markovian Langevin equation, I obtain general expressions for the mean-squared displacement and the time-dependent diffusion coefficient that are directly related

We study experimentally the rheological behavior of carbon black (CB) suspensions in water at different ionic strengths and concentrations. We show by means of standard rheometry completed by local magnetic resonance imaging-rheometry that these suspensions first appear to be thixotropic yield stress fluids: they exhibit a yield stress increasing with the time of rest, their apparent viscosity decreases

Polymer chains in both dilute solutions and melts undergo cyclic rotation and retraction, which is known as tumbling, under steady shear flow. However, it is still not known how the individual molecules in melts rotate freely under the constraints caused by surrounding chains. In this work, a Brownian dynamics simulation is used to investigate the influences of the interchain interactions on the polymer

It is not straightforward to prepare a fiber reinforced composite in which reinforcing fibers are dispersed uniformly. The nonuniform distribution of the reinforcing fibers produces nonuniform viscosity of the composite and thus drives the breakup of the filament upon extension. However, this breakup is suppressed when the fiber length is large. By using Bachelor’s theory for the viscosity of fiber

The rheology of noncolloidal suspensions in superposed simple shearing and oscillatory shearing was explored. With a Newtonian matrix fluid, one would expect that G′ would be zero in an oscillatory flow, but this was not found; the action of Coulomb friction between the particles appears to cause an increment of G′ at lower frequencies. To understand this frictional effect, measurements of small and

A non-Brownian, inertialess, dense suspension of rigid hollow glass spheres is studied with time sweep oscillatory experiments. The measured apparent complex viscosity is shown to depend on the amplitude of the applied strain, in agreement with the literature, and, unexpectedly, also on the angular frequency. Two different regimes are individuated depending on the applied strain. For values smaller

The weight-average molecular weights of six native cellulose samples in ionic liquids were determined through steady shear viscosity measurements in the ionic liquid butyl methyl imidazolium chloride. The intrinsic viscosity [ η ] in ethyl methyl imidazolium acetate (EMImAc) is measured using a gravity-driven glass capillary viscometer and found to be independent of temperature in the range of 30–80 °C

We extend the single-chain slip-spring model developed by Likhtman [Macromolecules 38, 6128 (2005)] to describe the dynamics and rheology of entangled polymers to wormlike micellar solutions by incorporating chain breakage and rejoining, which are the key additional dynamics present in wormlike micellar solutions. We show that the linear rheological properties obtained from this micelle slip-spring