Thixotropic yield stress materials show a shear-induced solid-liquid transition at the yielding point, characterized by yield stress and yield strain. It is well known in the literature that the elastic modulus and the yield stress of thixotropic materials increase with aging time. In the current work, we propose a discussion on the brittleness of a suspension of swollen bentonite in water, focusing

Gelatin gels are known to be nonequilibrium systems, because of the continuous growth and rearrangements of physical junctions, even in the solidlike state. Establishing a relationship between the relative degree of cross-linking and macroscopic elasticity would be crucial in understanding, modeling, and predicting the transformation processes of gelatin solutions. Performing rheological experiments

Long-chained surfactant solutions have found widespread use in the oil and gas industry due to a host of attractive properties. In this paper, we characterize one such commercially used viscoelastic surfactant that forms a wormlike micellar gel at room temperature and a viscoelastic solution at higher temperatures. We probe both states by conducting linear and nonlinear rheological tests and analyze

Performances of rotational shear rheometers are sometimes limited to measuring low viscosity at high temperatures of water-based polymer solutions. These limitations are typically due to the instrument resolution, sample inertia, and volumetric effects. Moreover, such measurements are not possible for temperatures exceeding 80 °C because of evaporation phenomena leading to a distortion of the value

The thixotropy of cellulose nanocrystal (CNC) water suspensions is intrinsically dependent on the hierarchical structure of the suspension. The diverse hierarchies that comprise individual CNC nanoparticles and mesophase liquid crystalline domains, chiral nematic and nematic structures, contribute selectively to the rheological material response. Here, we combine rheology with polarized light imaging

Couette–Poiseuille (C–P) flow, which is driven by drag from a moving wall and a pressure gradient, can exist in different states depending on the relative strengths of the two above-mentioned factors. Of particular interest is the onset of flow reversal, which is characterized kinematically by a zero shear rate on the stationary wall. This study presents two different methods for obtaining the critical

Anisotropic fiber-reinforced composites are used in lightweight construction, which is of great industrial relevance. During mold filling of fiber suspensions, the microstructural evolution of the local fiber arrangement and orientation distribution is determined by the local velocity gradient. Based on the Folgar–Tucker equation, which describes the evolution of the second-order fiber orientation

Understanding changes to microstructural dynamics under nonlinear deformations is critical for designing flow processes of entangled polymeric fluids, motivating the development of experimental methods to probe strain- and rate- dependent modifications to relaxation mechanisms. Although orthogonal superposition rheometry (OSR) holds promise as such a probe, the ability to interpret the superposition

In polymeric materials subject to both polymerization reactions and flow, there can be a complex interplay between reactions and stress relaxation processes. For example, reversible scission reactions can “shuffle” stresses across the molecular weight distribution, narrowing the stress relaxation spectra and decreasing the typical stress relaxation time. In addition, flow can stretch chains and make

Recent experiments suggest that the terminal relaxation time τ ^ b of star-linear blends varies nonmonotonically with the weight fraction of the star polymer in the blend w s [Hall et al., Macromolecules 52, 7831 (2019)], when the linear polymer is more viscous than the star; i.e., the ratio of linear and star viscosities r η = η 0 , l / η 0 , s > 1. We used a fast slip link model called ecoSLM to

The effect of a spatially uniform magnetic field on the shear rheology of a dilute emulsion of monodispersed ferrofluid droplets, immersed in a nonmagnetizable immiscible fluid, is investigated using direct numerical simulations. The direction of the applied magnetic field is normal to the shear flow direction. The droplets' extra-stress tensor arising from the presence of interfacial forces of magnetic

A coarse-grained bead-spring-dashpot chain model with the dashpots representing the presence of internal friction is solved exactly numerically for the case of chains with more than two beads. Using a decoupling procedure to remove the explicit coupling of a bead’s velocity with that of its nearest neighbors, the governing set of stochastic differential equations are solved with Brownian dynamics simulations

In order to measure the extensional rheological properties of yield stress fluids, we developed a rheometrical approach based on the analysis of the deformations of a fluid extrudate flowing downward and breaking in successive elongated drops due to gravity. Assuming the gradients of longitudinal velocity in radial planes are negligible, the local instantaneous strain rate is deduced from the variations

It has been known for some time that mechanical pretreatments of melts of long-chain branched polymers can increase the melt index and reduce the extrudate swell. This effect is not due to changes of the molar mass, its distribution, or the degree of branching because it may be reversed by long-term annealing or dissolution of the polymeric material and subsequent precipitation. Furthermore, molecular

The flow behavior of nanocrystalline cellulose (CNC) hydrogels in the presence of a monovalent electrolyte (NaCl) as a function of CNC and salt concentration is explored using a variety of linear and nonlinear rheological tests. We have first observed an apparent “slip yield stress” at small wall shear stress values that is mainly due to the onset of solidlike slippage of the hydrogels before their

Although the rheology of strong colloidal gels is predominantly concerned with either pure shear or pure compressive deformation, the vast majority of practical applications involves an arbitrary combination of shear and compressive stresses and strains. This situation demands a tensorial rheology of colloidal suspensions, where the multidimensional response of these complex materials to arbitrary

We perform immersed-boundary-method numerical simulations of small amplitude oscillatory shear flow of suspensions of monodisperse noncolloidal rigid spherical particles in non-Newtonian liquids from the dilute to the concentrated regime. We study the influence of suspending liquid inertia and rheology and particle concentration on the computationally measured storage and loss moduli of the suspensions

Rubber nanocomposites experiencing dynamic shears at large strain amplitudes (γ) exhibit the nonlinear Payne effect featured by decays of storage and loss moduli (G′ and G″) or by G′ decay accompanied with G″ overshoot near a critical strain amplitude. The occurrence of the Payne effect has been assigned to damages of “filler network” and rubber-filler interfacial interactions for a long time and to

We present a combined simulation and experimental study of the structure and dynamics of dilute, semidilute, and concentrated graphene oxide aqueous alkaline dispersions. These materials behave as lyotropic systems, with phase ordering as the concentration increases. The sheet spacing in the ordered phases is much broader than that expected by the classical Derjaguin–Landau–Verwey–Overbeek theory.

In this work, the effect of cellulose filaments (CFs) dispersion on the relaxation behavior of thermoplastics matrices was studied. The dispersion state of polystyrene/CF composites produced by two different processing methods, leading to two different dispersion qualities, was assessed using scanning electron microscopy (SEM), transmission electron microscopy, and small amplitude oscillatory shear

Fourier-transform infrared (FTIR) spectroscopy is a common tool for determining, both qualitatively and quantitatively, the chemical composition of a material in the solid, liquid, or gas phase. It is additionally used as a technique to monitor the rate of chemical changes. These chemical changes can have rheological relevance, e.g., polymerization kinetics, rubber crosslinking, or epoxy curing, just

Owing to nonlinear viscoelasticity, materials often show characteristic features that resemble those of thixotropy. This issue has been debated in the literature over the past several decades, and several experimental protocols have been proposed to distinguish thixotropy from viscoelasticity. In this work, we assess these protocols by carrying out experiments using polymer solutions, thixotropic clay

In well-entangled living polymers, there is a complex relationship between reversible polymerization reactions and stress relaxation dynamics. This relationship is already well-understood in the “fast-breaking” limit, where polymers tend to break apart much faster than they can relax interior tube segments by reptation. For well-entangled living polymers that are not necessarily fast-breaking, we introduce

Although bead microrheology experiments are routinely used to characterize the viscoelasticity of complex matter, their simulation analog—probe rheology molecular simulations—has been scarcely used since the system characteristics required for its robust implementation are not established in the literature. We address this issue by analyzing an active probe rheology simulation setup consisting of a

Isotactic polypropylene (iPP) melts are industrial semicrystalline polymers whose processing typically involves strong shear flows. The study of the rheological response of iPP melts, well beyond the linear viscoelastic limit, is limited by edge fracture, which manifests in rotational rheometers. In this work, we used a reflection polariscope under shear to detect the onset shear rate at which edge

A new pressure sensor array, positioned on the bottom plate of a standard torsional rheometer, is presented. It is built from a unique piezo-capacitive polymeric foam and consists of 25 capacitive pressure sensors (of surface 4.5 × 4.5 mm 2 each) built together in a 5 × 5 regular array. The sensor array is used to obtain a mapping of the normal stresses in complex fluids, which dramatically extends

A multiparticle Brownian dynamics simulation algorithm with a Soddemann–Dünweg–Kremer potential that accounts for pairwise excluded volume interactions between both backbone monomers and associating groups (stickers) on a chain is used to describe the static behavior of associative polymer solutions, across a range of concentrations into the semidilute unentangled regime. Predictions for the fractions

Polymers bearing associative groups (APs) are characterized by their fantastic viscoelastic behaviors. In a work recently published by our group [Jiang et al., Macromolecules 53, 3438–3451 (2020)], a single chain sticky Rouse model (SRM) is proposed to describe the linear viscoelasticity of APs without the entanglement effect. In this work, equilibrium molecular dynamics simulation of an unentangled

Polyelectrolyte (PE) solutions, which are charged polymers in polar solvents, are ubiquitous and essential to life. Due to the electrostatic interactions among the charged monomers and mobile ions, the dependence of the rheological properties on the polymer concentration of PE solutions differs significantly from that of solutions of uncharged macromolecules. In addition, salt in PE solutions, whether

Blends containing 85 wt. % of an amorphous polylactide with 15 wt. % of three different semicrystalline PLA (cPLA) grades with different crystallizabilty were separately blended via a twin-screw extruder below the melting temperature of the cPLAs. The extrudates were either directly pelletized or pelletized after being drawn at a draw ratio of 10. The small amplitude oscillatory shear behavior of the

We use Brownian dynamics (BD) simulations and single molecule experiments to investigate the influence of topological constraints and hydrodynamic interactions on the dynamics and rheology of solutions of ring-linear polymer blends at the overlap concentration. We find agreement between simulation and experiment in which rings in solution blends exhibit large conformational fluctuations. A subpopulation

We study the dynamics of nanoparticles in semidilute solutions of ring and linear polymers using hybrid molecular dynamics–multiparticle collision dynamics simulations. The dynamics of the monomers, the polymer centers-of-mass, and the nanoparticles coincide for these two architectures for solutions of the same monomer concentration. The long time diffusivities of the nanoparticles follow the predictions

Ring polymers exhibit unique flow properties due to their closed chain topology. Despite recent progress, we have not yet achieved a full understanding of the nonequilibrium flow behavior of rings in nondilute solutions where intermolecular interactions greatly influence chain dynamics. In this work, we directly observe the dynamics of DNA rings in semidilute ring-linear polymer blends using single

We report a comprehensive study on the molecular conformation and dynamics of very large poly(ethylene oxide) rings in the melt: (i) for all rings, independent of the ring size, by small angle neutron scattering we observe a crossover from a strong Q-dependence at intermediate Q to a Q − 2 dependence at higher Q. Constructing a generic model including a crossover from Gaussian statistics at short distances

We present a comprehensive experimental rheological dataset for purified entangled ring polystyrenes and their blends with linear chains in nonlinear shear and elongation. In particular, data for the shear stress growth coefficient, steady-state shear viscosity, and first and second normal stress differences are obtained and discussed as functions of the shear rate, as well as molecular parameters

The influence of distance dependent excluded volume interactions (EVIs) on the conformational properties of ring polymers is investigated within the principles of Rouse–Zimm theory. This study characterizes the structural features, i.e., the mean square radius of gyration, static structure factor, scattering intensity, fractal dimensions, and the mean square intermonomer distances of ring polymers

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

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

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

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