Journal of Rheology, Volume 65, Issue 3, Page 491-492, May 2021.

Colloidal gels made of carbon black particles dispersed in light mineral oil are “rheo-acoustic” materials, i.e., their mechanical and structural properties can be tuned using high-power ultrasound, sound waves with submicrometer amplitude and frequencies larger than 20 kHz. The effects of high-power ultrasound on the carbon black gel are demonstrated using two experiments: rheology coupled to ultrasound

A model is presented to predict the linear viscoelastic rheology of hydrophobically modified adhesive soft particle glasses in an aqueous solution. The hydrophobes on the surfaces of particles in contact preferentially associate with each other, creating an adhesive force between particles. The extent of this adhesive force depends on the number of associating or physically bonded hydrophobes and the

In this work, we investigate the effect of interdroplet interaction on the rheological behavior of oil-in-water emulsions within a range of macro- to nano-droplet sizes and various volume fractions from dilute to concentrated regimes. We determine the total interdroplet interaction from electrostatic, van der Waals, and depletion attraction contributions. At constant surfactant concentration, the depth

Linear and nonlinear viscoelastic approaches are used to study multiphase biobased blends of poly(lactic acid), poly(amide 11), poly(ether-b-amide) (PEBA), and poly(ethylene oxide) (PEO) in a wide range of compositions. The novelty of this work resides in (a) the study of hybrid quaternary blends with droplet-matrix as well as cocontinuous morphology, (b) the effect of the PEO and PEBA blend components

From paints to food products, solvent evaporation is ubiquitous and critically impacts product rheological properties. It affects Newtonian fluids by concentrating any nonvolatile components and viscoelastic materials, which harden up. In both of these cases, solvent evaporation leads to a change in the volume of the sample, which makes any rheological measurements particularly challenging with traditional

Discontinuous shear thickening and dynamic shear jamming can be observed in the dense granular suspension. Here, we determine the criterion for the occurrence of shear jamming by studying the first normal stress difference N 1 of dense granular suspension in steady-state rheology. When N 1 = 0, the suspension is shear jammed, and the frictional contact dominates the framework. The jamming onset stress

Following a previous work investigating the flow-induced crystallization (FIC) of polybutylene terephthalate/polytetrahydrofuran (PBT/PTHF) multiblock copolymers under steady shear, we propose here to deal with the case of large amplitude oscillatory shear (LAOS). For this purpose, we focus on a single copolymer ( M w ¯ = 50 kg mo l − 1) made, in average, of a sequence of nine soft and eight hard segments

Using the retraction method of a deformed drop, the interfacial tension between polypropylene (PP) and two different molten metals (tin and the eutectic SnAgCu alloy) has been measured at 250 and 230 °C, respectively. Systematic rheological investigations of the materials under study enabled us to measure the viscosity of the polymer matrix and that of the metal liquids. A viscosity of 1.9 and 2 mPa s

The intramolecular relaxation dynamics of unconcatenated ring polymers in dilute solutions is theoretically investigated within the framework of the Rouse–Zimm theory. The excluded volume interactions (EVIs) between the nonbonded monomers are modeled by a harmonic potential, where the interaction parameter is evaluated from Flory’s mean-field approach. The hydrodynamic interactions (HIs) between the

Until the advent of the novel Enders catalysts, the nonlinear rheological characterization of polyethylene (PE) blends, containing up to 50 wt. % of ultra-high molecular weight PE (UHMWPE, with weight average molecular weight Mw > 106 g/mol) was unattainable. In this study, by melt blending of a commercially available high-density PE (polymer matrix) and PE-reactor-blends (RBs), multimodal PE blends

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

The dynamics of model colloidal gels under a steady shear flow is studied by means of a Brownian dynamics (BD) simulation while applying orthogonal superposition rheometry, which superimposes a small amplitude oscillatory flow orthogonal to the main flow direction. Orthogonal dynamic frequency sweep (ODFS) curves are obtained at various magnitudes of the main flow, which shows shear thinning behavior

Dynamic mechanical oscillatory shear measurements with torsional rectangular geometry are widely carried out in order to determine the mechanical properties of soft solid materials in a quick and practical way. This technique has the advantage of avoiding slip effects, thus being particularly attractive for testing stiff elastomers such as vulcanized rubber compounds. However, one of its drawbacks

The criterion for brittle fracture of entangled polymer liquids [Wagner et al., J. Rheol. 62, 221–223 (2018)] is extended by including the effects of finite chain extensibility and polymer concentration. Crack initiation follows from rupture of primary C–C bonds, when the strain energy of entanglement segments reaches the energy of the covalent bond. Thermal fluctuations will concentrate the strain

For the nanoparticle-filled polymers, weak attractive interactions between nanoparticles lead to agglomeration and even formation of a network of nanoparticles in the polymer matrix. Both the agglomeration and the deagglomeration (breakdown) of the particle network are affected by the shear flow, resulting in shear-induced liquid-solid (L-S) transition and shear-induced solid-liquid (S-L) transition

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