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

The discrete slip-link theory is a hierarchy of strongly connected models that have great success predicting the linear and nonlinear rheology of high-molecular-weight polymers. Three of the four parameters of the most-detailed model, which can be extracted from primitive-path analysis, give quantitative agreement with experimental data for all examined chemistries (polystyrene, polyisoprene, polybutadiene

Blood-derived products, particularly platelet-rich plasma (PRP), have received increased attention in the past several years due to their great potential as a therapy for osteoarthritis and tendon injuries. Therefore, characterizing the mechanical properties of PRP becomes important to better understand its therapeutic efficacy. This paper aims to investigate the rheological properties of PRP in order

Mixing, agglomerating, and milling of granular materials within a rotating drum is often performed in the cascading flow regime; however, the scaling behavior of these industrial applications remains poorly understood. It involves both centrifugal forces and an inertial surface flow with a curved profile. By means of discrete element simulations, we investigate the rheology of cascading flows in rotating

The viscosity of suspensions depends on the properties of the fluid, i.e., the matrix material as well as on the volume fraction and shape of embedded inclusions. Regarding this dependence, a micromechanics-based homogenization approach is presented, giving access to the resulting effective viscous properties, starting from well established homogenization schemes originally proposed for the linear-elastic

We present a theoretical and computational study of thixotropic yield-stress materials in cylindrical Couette flows using a novel fluidity-based constitutive model introduced by de Souza Mendes et al. [J. Nonnewtion. Fluid Mech. 261, 1–8 (2018)]. The model relies on measurable rheological properties to couple the equations of motion with an additional equation for the evolution of the material fluidity

We report shear startup data on solutions of entangled linear wormlike micelles, only differing in the concentration of a binding aromatic salt. Wormlike micelles behave similarly to ordinary polymers in fast shear flows, exhibiting pronounced overshoots as well as tiny undershoots in transient shear viscosity, before approaching the steady state. The analogy is here emphasized by successfully comparing

The evolution of viscoelastic properties near the sol-gel transition is studied by performing oscillatory rheological measurements on two different types of systems: a colloidal dispersion and a thermoresponsive polymer solution under isothermal and non-isothermal conditions. While undergoing sol-gel transition, both the systems pass through a critical point. An approach to the critical point is characterized

The authors report the rheology and shear flow velocity profiles of pseudo-ternary “lamellar gel networks” commonly found in cosmetic emulsions such as creams, lotions, and hair conditioners, consisting of the cationic surfactant behentrimonium methosulfate, a fatty alcohol mixture of cetyl and stearyl alcohol, and water at surfactant/fatty alcohol mole fractions ranging from 0.1 to 0.6 and water mass

Here, we report for the first time that resonance in dynamic-mode cantilever sensors persists in hydrogels and enables the real-time characterization of hydrogel viscoelastic properties and the continuous monitoring of sol-gel phase transitions (i.e., gelation and dissolution processes). Real-time tracking of piezoelectric-excited millimeter cantilever (PEMC) sensor resonant frequency (fair = 55.4 ± 8

In this work, the effect of rigid rods on the discontinuous shear thickening (DST) transition in mixtures of smaller isotropic-shaped (calcium carbonate—CC) and larger rod-like (polyamide or glass) particles dispersed in water is experimentally established. The CC suspension in water is considered as a shear thickening matrix filling the pores of the fiber network. The DST in the matrix originates

Asphaltenes are a class of high molecular weight aromatic compounds found in crude oil. They adsorb onto toluene-water interfaces and induce a spontaneous emulsification phenomenon, whereby stable water-in-oil emulsions form without the need of an external energy input. This work aims to control and understand the factors affecting spontaneous droplet formation in the presence of asphaltene adsorption

Motivated by the existence of conflicting results that can be found in the specialized literature, an experimental program was designed strictly following the definitions of thixotropy and antithixotropy provided by the International Union of Pure and Applied Chemistry. To test the validity of the implicitly assumed correspondence between steady state shear thinning and thixotropy, and steady state

Chemical crosslinking, physical associating, and filler filling play vital roles in nonlinear responses of rubbers under large amplitude oscillatory shear (LAOS). Herein, a systematical investigation was performed for polyisoprene rubber vulcanizates and compounds on the framework of LAOS analytical methods to quantify intra- and intercycle nonlinearities. It is shown that the Payne effect is featured

Viscoelastic shear properties of human vocal fold tissues were previously quantified by the shear moduli (G' and G″). Yet these small-strain linear measures were unable to describe any nonlinear tissue behavior. This study attempted to characterize the nonlinear viscoelastic response of the vocal fold lamina propria under large-amplitude oscillatory shear (LAOS) with a stress decomposition approach

The crystallization of a polymer melt is characterized by dramatic structural and mechanical changes that significantly impact the processing conditions used to generate industrially-relevant products. Relationships between crystallinity and rheology are necessary to simulate and monitor the effect of processing conditions on the properties of the final product. However, separate measurements of crystallinity

The rheological properties of a particle suspension can be substantially altered by adding a small amount of a secondary fluid that is immiscible with the bulk phase. The drastic change in the strength of these capillary suspensions arises due to the capillary forces, induced by the added liquid, leading to a percolating particle network. Using rheological scaling models, fractal dimensions are deduced