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Abstract: The Tonga‐Kermadec subduction zone exhibits the fastest observed trench retreat and convergence near its northern end. However, a paradox exists: despite the rapid trench retreat, the Tonga slab maintains a relatively steep dip angle above 400 km depth. The slab turns flat around 400 km, then steepening again until encountering a stagnant segment near 670 km. Despite its significance for understanding slab dynamics, no existing numerical model has successfully demonstrated how such a distinct slab morphology can be generated under the fast convergence. Here we run subduction models that successfully reproduce the slab geometries while incorporating the observed subduction rate. We use a hybrid velocity boundary condition, imposing velocities on the arc and subducting plate while allowing the overriding plate to respond freely. This approach is crucial for achieving a good match between the modeled and observed Tonga slab. The results explain how the detailed slab structure is highly sensitive to physical parameters including the seafloor age and the mantle viscosity. Notably, a nonlinear rheology, where dislocation creep reduces upper mantle viscosity under strong mantle flow, is essential. The weakened upper mantle allows for a faster slab sinking rate, which explains the large dip angle. Our findings highlight the utilizing rheological parameters that lead to extreme viscosity variations within numerical models to achieve an accurate representation of complex subduction systems like the Tonga‐Kermadec zone. Our study opens new avenues for further study of ocean‐ocean subduction systems, advancing our understanding of their role in shaping regional and global tectonics.

Glass-forming colloids consisting of soft core-shell particles were investigated experimentally under medium and large amplitude oscillatory shear (MAOS and LAOS) using Fourier transform rheology to decompose the stress signal into a series of higher harmonics. The anharmonicity of the stress response under MAOS and LAOS is quantified by the intensity of the third harmonic normalized to the fundamental (I 3 / 1 = I 3 / I 1) and within the intrinsic nonlinearity framework of the Q-parameter (Q 0 = lim γ 0 → 0 ⁡ (I 3 / 1 / γ 0 2)). Furthermore, the results of the strain amplitude dependence were compared to the literature showing the mechanical anharmonic behavior of the core-shell system being close to the behavior of ultrasoft systems. In the glassy state, I 3 / 1 shows an unusual scaling of I 3 / 1 ∝ γ 0 4 at low frequencies, similar to amorphous polymeric materials when they undergo plastic deformation. For investigating the frequency dependence of the anharmonicity in a specially designed binary mixture to test for critical behavior close to the glass transition as predicted by mode coupling theory (MCT) and extend the measurements to the glassy state, we used the frequency sweep MAOS methodology. Using this time-efficient method, the frequency dependence of a wide range of volume fractions and frequencies was investigated, finding the anharmonicity parameter Q 0 to be maximal in the region of the α -relaxation for colloidal liquids. The colloidal glasses do not exhibit a maximum in Q 0 , but an increase in Q 0 with decreasing frequency over the investigated region, as the α -relaxation slows down significantly in colloidal glasses. Predictions from MCT from the literature show agreement with the experimentally determined scaling laws. [ABSTRACT FROM AUTHOR]

We propose a predictive model for various sensory textures utilizing machine learning techniques based on the largest rheology and panel-tested sensory texture database ever assembled. In addition to the conventional rheological parameters typically measured in the cosmetics field, rheological parameters obtained from the large amplitude oscillatory shear (LAOS) sequence of physical processes (SPPs) and extensional rheology analyses are employed as feature variables for the predictive model. These feature variables are chosen to mimic real flow conditions during the usage of cosmetics, such as rubbing and tapping, as they are expected to contain more information related to sensory textures. It has been demonstrated that our prediction model, based on the random forest regression algorithm, can effectively predict five sensory textures: spreadability, thickness, softness, adhesiveness, and stickiness. We investigated the rheological characteristics crucial for determining each sensory texture through permutation and feature importance analyses. The important analysis highlighted the close correlation between rheological parameters from LAOS–SPP, extensional analyses, and sensory textures. By using this correlation, we interpret the perception of each sensory texture in the context of rheology.

The ability to accurately predict the rheological behavior of the blends of two incompatible polymers is critical to the polymer industry. The constitutive modeling of incompatible polymer blends requires understanding the structure and dynamics of the blends across different length scales. The polydispersity of chain length at the molecular level and nonuniformity of flow field due to dispersed domains at the mesoscopic level present significant challenges to this industrially relevant problem. This work proposes a modeling framework for linear and nonlinear rheology of industrial incompatible polymer blends with sea-island morphology. For the individual components, we adopt the Rolie-Double-Poly model and generate the relaxation spectrum from an optimized molecular weight distribution. We derive a new mixing rule without empirical parameters from the flow field analysis inside and outside the droplets. The phase interface, modeled by an ellipsoidal model, contributes to the apparent rheology only at low shear rates. Our modeling approach is verified by the shear and extensional rheology of eight polymer blends with a broad range of viscosity ratios (0.01–100). We also show that the model has the ability to predict the nonlinear rheological behaviors of incompatible polymer blends with known molecular weight distributions and phase morphology. [ABSTRACT FROM AUTHOR]

Modern geodynamics is based on the study of a large set of models, with the variation of many parameters, whose analysis in the future will require Machine Learning to be analyzed. We introduce here for the first time how a formulation of the Lattice Boltzmann Method capable of modeling plate tectonics, with the introduction of plastic non-linear rheology, is able to reproduce the breaking of the upper boundary layer of the convecting mantle in plates. Numerical simulation of the earth’s mantle and lithospheric plates is a challenging task for traditional methods of numerical solution to partial differential equations (PDE’s) due to the need to model sharp and large viscosity contrasts, temperature dependent viscosity and highly nonlinear rheologies. Nonlinear rheologies such as plastic or dislocation creep are important in giving mantle convection a past history. We present a thermal Lattice Boltzmann Method (LBM) as an alternative to PDE-based solutions for simulating time-dependent mantle dynamics, and demonstrate that the LBM is capable of modeling an extremely nonlinear plastic rheology. This nonlinear rheology leads to the emergence plate tectonic like behavior and history from a two layer viscosity model. These results demonstrate that the LBM offers a means to study the effect of highly nonlinear rheologies on earth and exoplanet dynamics and evolution.

Modern geodynamics is based on the study of a large set of models, with the variation of many parameters, whose analysis in the future will require Machine Learning to be analyzed. We introduce here for the first time how a formulation of the Lattice Boltzmann Method capable of modeling plate tectonics, with the introduction of plastic non-linear rheology, is able to reproduce the breaking of the upper boundary layer of the convecting mantle in plates. Numerical simulation of the earth’s mantle and lithospheric plates is a challenging task for traditional methods of numerical solution to partial differential equations (PDE’s) due to the need to model sharp and large viscosity contrasts, temperature dependent viscosity and highly nonlinear rheologies. Nonlinear rheologies such as plastic or dislocation creep are important in giving mantle convection a past history. We present a thermal Lattice Boltzmann Method (LBM) as an alternative to PDE-based solutions for simulating time-dependent mantle dynamics, and demonstrate that the LBM is capable of modeling an extremely nonlinear plastic rheology. This nonlinear rheology leads to the emergence plate tectonic like behavior and history from a two layer viscosity model. These results demonstrate that the LBM offers a means to study the effect of highly nonlinear rheologies on earth and exoplanet dynamics and evolution. [ABSTRACT FROM AUTHOR]

For physically gelled colloidal suspensions, there are two routes to transform the gel from solid to liquid. One is to raise the temperature, and the other is to increase the shear deformation. In this investigation, we found that the phase boundary of this solid-to-liquid transformation exhibits a surprising Z-shaped curve in the strain-temperature plane. This nonmonotonic feature in phase transition appears to be present in various nanoparticle-filled colloidal gels with significant differences in chemical composition, filler type, structure, particle shape, average diameter, and particle size distribution. By applying the Kraus model to the breakage and restoration of filler networks and comparing our findings to nonequilibrium glassy behavior, we found that this nonmonotonic phenomenon can be theoretically predicted by combining the glassy melting kinetics of filler networks at high temperatures with the viscosity-retarded dissociation between particles at low temperatures. [ABSTRACT FROM AUTHOR]

Abstract The 2011 Tohoku-oki earthquake produced the most well-recorded postseismic deformation of any megathrust earthquake in the world. Over the last decade, researchers have used a dense and widespread geodetic network of more than 1300 Global Navigation Satellite System (GNSS) stations inland, as well as the about 50 stations on the seafloor, to investigate the various deformation sources responsible for the observed crustal deformation. One of the contributing mechanisms to this crustal deformation is the stress relaxation of the viscoelastic mantle beneath the Japanese arc. As evident in experimental rock physics and geophysical observations, ambient mantle conditions and related rheology are expected to be heterogeneous in space. However, the contribution of such rheological heterogeneities to the postseismic deformation is still poorly understood. Here, we piece together several rheological heterogeneities inferred from the decade-long postseismic deformation of the 2011 Tohoku-oki earthquake. We reviewed more than twenty postseismic models to understand how viscoelastic earth can influence the postseismic surface deformation observed after the Tohoku-oki earthquake. Besides, we employed several synthetic models to tease out the contribution of individual rheological heterogeneities such as depth-dependent rheology of mantle wedge, oceanic asthenosphere, and low-viscosity zone beneath the volcanic front. We demonstrate that the vertical postseismic observation is the key to unravel rheological complexity beneath northeastern Japan. The broader vertical deformation pattern reveals the major viscosity contrast between backarc and forearc, and small-scale subsidence detects the presence of low-viscosity bodies related to arc magmatism. In short, this review paper provides a vista of three-dimensional heterogeneous rheology of viscoelastic earth. These rheological heterogeneities may play a crucial role in bridging the gap between our understanding of different phase of subduction zone earthquake cycle.

[Display omitted] Cyclodextrin (CD) can spontaneously build up the solid particle membrane with CD-oil inclusion complexes (ICs) by a self-assembly process. Sodium casein (SC) is expected to preferentially adsorb at the interface to transform the type of interfacial film. The high-pressure homogenization can increase interfacial contact opportunities of the components, which promote the phase transition of the interfacial film. We added SC by sequential and simultaneous orders to mediate the assembly model of the CD-based films, examined the patterns in which the films adopt phase transitions to retard emulsion flocculation, and studied the physic-chemical properties of the emulsions and films from the structural arrest, interface tension, interfacial rheology, linear rheology, and nonlinear viscoelasticities through Fourier transform (FT)-rheology and Lissajous-Bowditch plots. The interfacial and large amplitude oscillatory shear (LAOS) rheological results showed that the films changed from jammed to unjammed. We divide the unjammed films into two types: one is SC dominated liquid-like film, which is fragile and related to droplet coalescence; the other is cohesive SC-CD film, which helps droplet rearrangement and retards droplet flocculation. Our results highlight the potential of mediating phase transformation of interfacial films to improve emulsion stability. [ABSTRACT FROM AUTHOR]

Small-amplitude oscillatory shear (SAOS) tests provide a complete framework to characterize a viscoelastic material in the linear regime. Large-amplitude oscillatory shear (LAOS) tests in which the material is subjected to large sinusoidal strain amplitudes, and the resulting nonsinusoidal stress waveform is analyzed, have recently become an area of research in the characterization of nonlinear viscoelastic behavior. LAOS tests have been applied on various types of viscoelastic materials and a Fourier-transform analysis has been used to characterize the nonlinearity by the occurrence of higher-order harmonics. Other works have attempted to improve on the existing Fourier-transform method and have also introduced new methods to characterize the nonlinearity, which can provide a physical significance to the parameters involved. While much soft matter has been examined within the various LAOS frameworks, very few attempts have been made to describe the behavior of glassy polymers within the LAOS framework. Here, we report the results of LAOS experiments in which we explore the nonlinear response of a glassy polymethyl methacrylate (PMMA) at 22 °C. We look at the behavior both qualitatively and quantitatively using Lissajous–Bowditch (LB) loops, Fourier-transform rheology (FTR), and Chebyshev-polynomial descriptions of behavior. The stress responses from the LAOS tests are also compared with those predicted by the BKZ nonlinear constitutive model. We report the absolute intensity of the harmonics and their variation with the strain amplitude. For PMMA, the normalized third-harmonic intensity, which is one characteristic of the nonlinearity, does not follow a quadratic dependence on strain amplitude as observed in several other materials. The Chebyshev-polynomial method provides a physical interpretation via the normalized third-order Chebyshev coefficients that were calculated using the MITLAOS MATLAB program. Normalized elastic Chebyshev coefficients showed strain softening, while shear-softening behavior was observed from normalized viscous Chebyshev coefficients for PMMA with an increase in strain amplitude. We have also compared the FTR and Chebyshev methodologies for a purely elastic material and have shown that the Chebyshev analysis can effectively separate the nonlinearity as contributed by elastic and viscous parts, while the harmonic FT analysis characterizes nonlinearity as a combined effect. [ABSTRACT FROM AUTHOR]

The 2011 Tohoku-oki earthquake produced the most well-recorded postseismic deformation of any megathrust earthquake in the world. Over the last decade, researchers have used a dense and widespread geodetic network of more than 1300 Global Navigation Satellite System (GNSS) stations inland, as well as the about 50 stations on the seafloor, to investigate the various deformation sources responsible for the observed crustal deformation. One of the contributing mechanisms to this crustal deformation is the stress relaxation of the viscoelastic mantle beneath the Japanese arc. As evident in experimental rock physics and geophysical observations, ambient mantle conditions and related rheology are expected to be heterogeneous in space. However, the contribution of such rheological heterogeneities to the postseismic deformation is still poorly understood. Here, we piece together several rheological heterogeneities inferred from the decade-long postseismic deformation of the 2011 Tohoku-oki earthquake. We reviewed more than twenty postseismic models to understand how viscoelastic earth can influence the postseismic surface deformation observed after the Tohoku-oki earthquake. Besides, we employed several synthetic models to tease out the contribution of individual rheological heterogeneities such as depth-dependent rheology of mantle wedge, oceanic asthenosphere, and low-viscosity zone beneath the volcanic front. We demonstrate that the vertical postseismic observation is the key to unravel rheological complexity beneath northeastern Japan. The broader vertical deformation pattern reveals the major viscosity contrast between backarc and forearc, and small-scale subsidence detects the presence of low-viscosity bodies related to arc magmatism. In short, this review paper provides a vista of three-dimensional heterogeneous rheology of viscoelastic earth. These rheological heterogeneities may play a crucial role in bridging the gap between our understanding of different phase of subduction zone earthquake cycle. [ABSTRACT FROM AUTHOR]

Linear and non-linear rheological properties were examined for in-reactor alloy samples composed of isotactic polypropylene (iPP), ethylene-propylene rubber (EPR), and polyethylene (PE). The samples were prepared through two- or three-stage sequential polymerization, where iPP, as the majority, was synthesized in the first stage, and either EPR or PE, as the minority, was synthesized in the second or third stage. Above Tm of both PE and iPP, the linear viscoelasticity shows two relaxation processes, where the fast and slow processes are attributable to the relaxation of the iPP component and that of the EPR/PE domains, respectively. Both the damping behavior upon applying the step-strain measurements and the shear-thinning behavior under the shear-rate sweep measurements are strongly related to the different degrees of nonlinearity of the two relaxation processes. [ABSTRACT FROM AUTHOR]

Molecular interactions determine the microstructure of food, as well as its response to deformation and flow. In order to design efficient processing equipment, to produce high-quality, stable end products, to predict textural and sensory properties, and to ensure consumer acceptance, the characterization of food rheology is essential. Deformations are rapid and large during the processing of foods and during consumption. In food studies, large amplitude oscillatory shear (LAOS) has become increasingly popular due to its ability to mimic real-life processes. When food is subjected to dynamic oscillatory shear tests, a sinusoidal deformation is applied, the mechanical stress (or strain) is probed, and the response is recorded. This chapter summarize main methods to extract meaningful rheological parameters from complex LAOS response of selected food materials. A time-resolved nonlinear rheology method, sequence of physical processes (SPP), gave detailed interpretations of transient microstructures, whereas the Fourier Transform coupled with Chebyshev decomposition (FTC) method provide static measurements at specific strains. LAOS behavior and its relationship to food microstructures and texture still needed to be studied in depth. By constructing more accurate mechanical models of complex food systems, the fundamental knowledge can be applied to evaluate the nonlinear rheology of food for consumer acceptance and efficient processing.

This study was to investigate the impact of granule size, amylose content, and starch molecular characteristics on pasting and rheological properties of starch paste/gels in neutral (water) and sugar–acid systems. Normal rice starch (RS), waxy rice starch (WRS), normal tapioca starch (TS), and waxy tapioca starch (WTS) representing small-granule starches and intermediate-granule starches respectively, were used in the study. Impacts of granule size, AM content, and their synergistic effects resulted in different starch susceptibility to acid hydrolysis and interactions between starch and sucrose-water, yielding different paste viscosities in both systems. The high molecular weight ( M w ¯ ) and linearity of amylopectin and amylose molecules increased the consistency of starch pastes. RS produced a stronger and more brittle gel than other starch gels in both neutral and sugar–acid systems. The results indicated the impact of the effect of granule size and amylose content on starch gel behaviors. Properties of waxy starch gels were mainly governed by amylopectin molecular characteristics, especially in the sugar–acid system. Adding sugar and acid had minor impacts on starch gel behaviors in the linear viscoelastic (LVE) region but were most evident in the nonlinear response regime of starch gels as shown in the Lissajous curves at large oscillatory strain. [ABSTRACT FROM AUTHOR]

Soft particulate gels can reversibly yield when sufficient deformation is applied, and the characteristics of this transition can be enhanced or limited by designing hybrid hydrogel composites. While the microscopic dynamics and macroscopic rheology of these systems have been studied separately in detail, the development of direct connections between the two has been difficult, particularly with regard to the nonlinear rheology. To bridge this gap, we perform a series of large amplitude oscillatory shear (LAOS) numerical measurements on model soft particulate gels at different volume fractions using coarse-grained molecular dynamics simulations. We first study a particulate network with local bending stiffness and then we combine it with a second component that can provide additional cross-linking to obtain two-component networks. Through the sequence of physical processes (SPP) framework, we define time-resolved dynamic moduli, and by tracking the changes in these moduli through the period, we can distinguish transitions in the material behavior as a function of time. This approach helps us establish the microscopic origin of the nonlinear rheology by connecting the changes in dynamic moduli to the corresponding microstructural changes during the deformation including the nonaffine displacement of particles, and the breakage, formation, and orientation of bonds. [ABSTRACT FROM AUTHOR]

This work was designed to illustrate the differences in the dispersed phase that affect the emulsion stability. The effect of oil types including soy oil, corn oil, rapeseed oil, sunflower oil, and flaxseed oil on the stability of the emulsion stabilized by modified MP (sonication after crosslinking treatment) was investigated. Results showed that the differences in fatty acid composition in the oil phase would affect the interaction between the oil phase and modified MP. Emulsion in the P-flaxseed group (with higher linolenic acid) showed lower TSI values, smaller protein-coated oil droplets, higher adsorbed protein content, storage modulus, and small elastic Lissajous curve area than other emulsion groups. While the P-rapeseed (with higher oleic acid) and P-sunflower (with higher linoleic acid) groups had large droplet sizes, poor emulsion stability, and rheological behavior. Correspondingly, the higher θo/w (86.97°), h f , π (21.55 mN/m), K diff , K R , E d , E-π slope (3.22), and linear interfacial Lissajous plot in the P-flaxseed group indicated modified MP was preferred to adsorb on the surface of flaxseed oil to form an elastic-dominated interfacial protein film with higher deformation resistance. Furthermore, the poorer interfacial adsorption behavior and easily collapsed interfacial film further proved the poor emulsion stability of the P-rapeseed and P-sunflower groups. Therefore, differences in fatty acid compositions of oil phases impacted the interfacial adsorption characteristics of the modified MP, thereby influencing the emulsion stability. [Display omitted] • Differences in fatty acid composition of oil phases affected the emulsion stability. • Shear and interfacial dilatation rheological behaviors of emulsion were studied. • Interfacial protein film dominated the rheology and stability of emulsion. • The emulsion fabricated by the modified MP and flaxseed oil had the best stability. [ABSTRACT FROM AUTHOR]

Crumpled systems (CSs) can be used as building blocks of mechanical metamaterials with low sensitivity to defects. But to exploit the potential of CSs for novel applications, extensive understanding of the physics of these systems is needed and, so far, the shear response of CSs has not been studied. Here we study the shear response of CSs via short/large amplitude oscillatory shear (SAOS/LAOS) while investigating the effect of several parameters. The training of crumpled paper reduced long-range correlations and resulted in an increase of the shear modulus with compaction, not observed for untrained paper. The presence of stacked layers parallel to the shear direction, in contrast to those positioned perpendicularly, resulted in lower shear storage modulus and increased energy dissipation through layers sliding. Reducing the surface friction allowed for easier internal rearrangements during shear deformations. In general, the shear resistance increases less with the increasing level of compaction than the compaction stiffness. However, it can be tuned by friction between the layers and their orientation. The estimated Poisson’s ratio of CSs reveals their auxetic nature. Our results pave the way to better understand the full mechanical response of CSs and tune their desired properties for practical applications.

We investigate the linear and nonlinear shear rheology of a marginally entangled H-polymer melt and two solutions made by diluting high molecular weight H-polymers in linear oligomer. In order to approach a nearly unentangled state, dilution is conducted at volume fractions such that the two solutions attain a similar number of entanglements of the melt. Start-up shear experiments demonstrate that the nonlinear behavior of the H-polymer melt is analogous to that of a linear melt with comparable span chain length. Concerning solutions, the increase of chain elasticity in fast flows, coupled with a lesser role of monomeric friction reduction, allows to attain strong stretch in start-up shear tests. As a result, transient strain hardening occurs. Furthermore, a failure of the Cox-Merz rule is observed for the solutions, which indicates that they better conform to a FENE-Rouse chain behavior compared to melts. [ABSTRACT FROM AUTHOR]

An orientation-stretch-coupled constitutive equation is suggested for symmetric Cayley tree-like dendrimers, which can self-consistently describe the linear relaxation spectrum and nonlinear viscoelastic behavior. The molecular stress is determined by orientation-stretch-coupled conformation tensors of all segments. The linear relaxation spectrum is determined according to hierarchical arm retraction with branch point hopping and dynamic tube dilation. Under strong flows, the orientation relaxation time and the stretch relaxation time are affected by the convective constraint release effect and branch point withdrawal. The coupling between segmental orientation and stretch in each generation is represented in the evolution of the coupled conformation tensor, while the possible stretch coupling among different generations is ignored. The predictions on both linear and nonlinear rheological behaviors are consistent with experiments, proving the rationality in treating coupling problems. [ABSTRACT FROM AUTHOR]

Flocculation is a type of aggregation where the surfaces of approaching droplets are still at distances no closer than a few nanometers while still remaining in close proximity. In a high internal-phase oil-in-water (O/W) emulsion, the state of flocculation affects the bulk flow behavior and viscoelasticity, which can consequently control the three-dimensional (3D)-printing process and printing performance. Herein, we present the assembly of O/W Pickering high-internal-phase emulsions (Pickering-HIPEs) as printing inks and demonstrate how depletion flocculation in such Pickering-HIPE inks can be used as a facile colloidal engineering approach to tailor a porous 3D structure suitable for drug delivery. Pickering-HIPEs were prepared using different levels of cellulose nanocrystals (CNCs), co-stabilized using "raw" submicrometer-sized sustainable particles from a biomass-processing byproduct. In the presence of this sustainable particle, the higher CNC contents facilitated particle-induced depletion flocculation, which led to the formation of a mechanically robust gel-like ink system. Nonetheless, the presence of adsorbed particles on the surface of droplets ensured their stability against coalescence, even in such a highly aggregated system. The gel structures resulting from the depletion phenomenon enabled the creation of high-performance printed objects with tunable porosity, which can be precisely controlled at two distinct levels: first, by introducing voids within the internal structure of filaments, and second, by generating cavities (pore structures) through the elimination of the water phase. In addition to printing efficacy, the HIPEs could be applied for curcumin delivery, and in vitro release kinetics demonstrated that the porous 3D scaffolds engineered for the first time using depletion-flocculated HIPE inks played an important role in 3D scaffold disintegration and curcumin release. Thus, this study offers a unique colloidal engineering approach of using depletion flocculation to template 3D printing of sustainable inks to generate next-generation porous scaffolds for personalized drug deliveries.

In this study, the nonlinear behavior of carbon black-filled polybutadiene solutions under large-amplitude oscillatory shear is investigated. The results show that in the nonlinear regime, the third harmonic intensity, as measured by the ratio of the third to the first harmonics I3/I1, decreases significantly above a critical concentration ϕc of the polymer in the matrix, which results in the amplitude stress deviating strongly from the linear dependence of strain, while the time dependence of stress remains sinusoidal. Increasing the filler particle size significantly decreases the critical ϕc. However, increasing the filler loading basically has no effect on the transition to linear-nonlinear dichotomy. This transition happens when the mesh size ξ of the entangled polymer network in the matrix becomes smaller than the primary filler particle size. Above ϕc, the topological hindrance of the entangled polymer chains apparently considerably slows down the recovery speed of the broken filler network in the material. Hence, the quasisinusoidal response in the system that has a strain-dependent modulus is probably due to the restoration of the broken filler network requiring longer than the time scale of a typical dynamic perturbation. [ABSTRACT FROM AUTHOR]

This work aimed to reveal the effect of heat treatment on the stability of ultrasound-assisted cross-linked myofibrillar protein-stabilized emulsion and its potential application as a filler phase. The interfacial dilatational rheology, emulsion droplets, linear and nonlinear shear rheological properties, microrheological properties, and tribological properties of emulsion fabricated by the original myofibrillar protein (MP) (NA), crosslinked MP (NAG), and sonication after crosslinked MP (MPGU) were determined at the heat temperature of 40 °C, 60 °C, and 80 °C. Results indicated that heat treatment would affect the stability and processing adaptability of the emulsion. The elasticity and strength of the interfacial film were enhanced with the treated temperature increased from 40 °C to 80 °C, and the MPGU group showed a more linear shape of interfacial Lissajous plot than the other groups even at large amplitudes. Based on the good interfacial properties, the MPGU group had the smaller emulsion droplets with more protein-coated, and the network structure was formed only at 80 °C. For the rheological properties, the lower apparent viscosity, elastic index (EI), and macroscopic viscosity index (MVI) in the MPGU group indicated the formation of a more stable emulsion. Furthermore, the lower closed area of Lissajous curves and friction coefficient for the MPGU group also proved the highest stability and lubrication of the emulsion after heat treatment. Therefore, this study indicated that ultrasound-assisted cross-linked myofibrillar protein-stabilized emulsions had good thermal stability and processing adaptability, which contributed to the fabrication of stable emulsion-filled foods. [Display omitted] • Sonication after crosslinking obviously improved the heat stability of MP emulsion. • Response of emulsions to three denaturation temperatures of MP was investigated. • Heat treatment strengthened the stiffness and lubrication of MP emulsion. • Combined rheology and tribology reveal the potential of emulsions as filler phases. [ABSTRACT FROM AUTHOR]

Polysaccharides are used in starch-based product formulations to enhance the final quality of food products. This study examined the interaction mechanisms in Ficus pumila polysaccharide (FPP) and wheat starch (WS) gel systems with varying FPP concentrations using linear and nonlinear rheological analysis. Physicochemical structural analyses showed non-covalent FPP-WS interactions, strengthening hydrogen bonding between molecules and promoting water binding and ordered structure generation during WS gel aging. Small amplitude oscillatory shear analyses revealed that elevated FPP concentrations led to increased storage modulus (G'), loss modulus (G"), critical strains (From 29.02 % to 53.32 %) and yield stresses (From 0.94 Pa to 30.97 Pa) in the WS gel system, along with improved resistance to deformation and short-term regeneration. In the nonlinear viscoelastic region, FPP-WS gels shifted from elastic to viscous behavior. Higher FPP concentrations displayed increased energy dissipation, strain hardening (S>0, e 3 /e 1 > 0) and shear thinning (T<0, v 3 /v 1 <0). FPP contributes more nonlinearity in the dynamic flow field as showed by the high harmonic ratio, with a larger I 3 /I 1 values overall. This study highlights FPP's potential in starch gel food processing, and offers a theoretical basis for understanding hydrocolloid-starch interactions. [ABSTRACT FROM AUTHOR]

In this study, mesoscopic sized fractal assembly (FA) particles were prepared using whey protein isolate; the cold-set gelation properties of FA particles were investigated in-depth. Two types of FA particles (FA-62 and FA-90) with different mean sizes were synthesized through controlled thermal treatment of whey protein solutions at two concentrations (62 g/L and 90 g/L). Particle characteristics e.g. hydrodynamic radius, ζ-potential and surface hydrophobicity were dependent on pH and structure of FA. Transmission electron microscopy (TEM) observation confirmed the fractal morphology and small-angle X-ray scattering (SAXS) analysis suggested an internal fractal structure for the obtained FA particles. Eight cold-set FA protein gels (2 % w/v) were manufactured by controlling two gelling factors at two levels: pH (5.8 and 7.0) and Ca2+ content (5 mM and 10 mM). Rheological characteristics in the large amplitude oscillatory shear regime revealed that pH 7.0 gels were softer and elastic while pH 5.8 gels were harder and brittle. Rheology Pipkin diagrams demonstrated that the strain softening/stiffening and the shear-thinning/thickening behaviors may be fine-tuned by manipulating the key gelation factors: e.g. FA structure, pH, and Ca2+. The entrainment speed-dependent friction coefficient curves showed that at an intermediate velocity regime (6–250 mm s−1), FA-90 particles induced hydrogels had superior lubrication effect compared to FA-62 gels. This work demonstrated a food structure design approach regarding tuning texture and lubrication properties of protein gels without changing protein content and protein composition. The optimized protein hydrogels may be used as texturizer for "cleaner label" food formulas and/or as delivery system for carrying micronutrients. [Display omitted] • Fractal assemblies were constructed from WPI through controlled thermal treatment. • TEM and SAXS techniques revealed fractal morphology and internal fractal dimension. • Cold-set whey protein gels (2 % w/v protein) had superior phase stability. • Rheological properties were tunable by altering protein particle size, pH, and Ca2+. • Lubrication behavior of cold-set WPI gels was governed by protein assembly structure. [ABSTRACT FROM AUTHOR]

[Display omitted] • Structural distinction of oleogel-based emulsion was confirmed by rheological technique. • Formation of crystal networks in emulsion was investigated by temperature sweep test. • Chebyshev coefficients analysis of LAOS showed that yielding was a broad transition. • Viscoelastic properties of oleogel-based emulsion were improved by modulating external factors. This study reported oleogel-based emulsions (OGEs, W/O) stabilized by carnauba wax. The effects of different external factors (heating temperature, crystallization temperature, and shear application during crystallization) on the microstructure and linear/nonlinear rheological properties of OGEs were investigated. Microstructural observation suggested that the OGEs had a uniform droplet distribution, and the carnauba wax crystals trapped oil in the continuous phase. The gelatinized oil phase allowed the OGEs to have a solid appearance and typical yielding behavior. The small amplitude oscillation shear analysis showed that lower heating temperature, higher crystallization temperature, and suitable shear application resulted in a stronger, more stable, and tighter packed network structure and better resistance to deformation of the OGEs. For nonlinear behavior, the elastic dominant behavior of OGEs transformed into viscous dominant behavior at large strain amplitudes, accompanied by more energy dissipation, strain stiffening, and a transition from shear thickening to shear thinning. [ABSTRACT FROM AUTHOR]

Extensive molecular simulations are applied to characterize the equilibrium dynamics, entanglement topology, and nonlinear extensional rheology of symmetric ring-linear polymer blends with systematically varied ring fraction ϕ R. Chains with degree of entanglement Z ≈ 14 are mixed to produce 10 well-entangled systems with ϕ R varying from neat linear to neat ring melts. Z is large enough that except for very large ϕ R , the rings are threaded by multiple linear chains in equilibrium. Primitive path analysis is used to visualize and quantify the structure of the composite ring-linear entanglement network. We measure the quantity of ring-linear threading and linear-linear entanglement as a function of ϕ R and identify with simple arguments a ring fraction ϕ R ≈ 0.4 where the topological constraints of the composite entanglement network are maximized. These topological analyses are used to rationalize the ϕ R -dependence of ring and linear chain dynamics, conformations, and rheology. Simulations of startup uniaxial elongation flows demonstrate the extensional stress overshoot observed in recent filament stretching experiments and characterize how it depends on the blend composition and entanglement topology. The overshoot is driven by an overstretching and recoil of ring polymers due to the convective unthreading of rings from linear chains. [ABSTRACT FROM AUTHOR]

This study examines the nonlinear rheology properties of telechelic ionomers with connecting ions at the chain ends. Our previous studies revealed that these telechelic ionomers relaxed in a hierarchical way depending on the average number of connecting ionic groups per chain end m. The terminal relaxation time increased with m because the dissociation was slower for the chain end with more connecting ions. In this study, the stress growth and damping functions are examined for these telechelic ionomer samples and a reference conventional telechelic sample having strictly one ion per chain end, both based on poly(isobutyl acrylate). During both the steady shear and elongation measurements, the stress overshoots are observed, and the corresponding strains at the stress overshoots, γpeak and εH,peak, are insensitive to the Weissenberg number Wi for W i ≫ 1. This feature suggests that γpeak or εH,peak are critical strains for the induction of dissociation, which is rationalized by the phenomenological analysis of the yielding stress based on the von Mises criterion. The approximate time-strain separability was surprisingly observed for the telechelic ionomer networks with a moderate m, which may be due to the fact that, although the high strain leads to a rupture of strand, the network structure has been maintained and its terminal relaxation is governed by the ionic dissociation (at least in the strain range of our measurements). These arguments are supported by the proper normalization of damping functions obtained for different samples using γ/γpeak as the horizontal axis. [ABSTRACT FROM AUTHOR]

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 (molar mass, blend composition, and decreasing molar mass of linear component in the blend). Over the extended parameter range investigated, rings do not exhibit clear transient undershoot in shear, in contrast to their linear counterparts and ring-linear blends. For the latter, the size of the undershoot and respective strain appear to increase with the shear rate. The universal scaling of the strain at overshoot and fractional overshoot (the ratio of the maximum to the steady-state shear stress growth coefficient) indicates subtle differences in the shear-rate dependence between rings and linear polymers or their blends. The shear thinning behavior of pure rings yields a slope nearly identical to predictions (−4/7) of a recent shear slit model and molecular dynamics simulations. Data for the second normal stress difference are reported for rings and ring-linear blends. While N2 is negative and its absolute value stays below that of N1, as for linear polymers, the ratio –N2/N1 is unambiguously larger for rings compared to linear polymer solutions with the same number of entanglements (almost by a factor of 2), in agreement with recent nonequilibrium molecular dynamics simulations. Furthermore, –N2 exhibits slightly weaker shear rate dependence compared to N1 at high rates, and the respective power-law exponents can be rationalized in view of the slit model (3/7) and simulations (0.6), although further work is needed to unravel the molecular original of the observed behavior. The comparison of shear and elongational stress growth coefficients for blends reflects the effect of ring-linear threading, which leads to significant viscosity enhancement in elongation. Along the same lines, the elongational stress is much larger than the first normal stress in shear, and their ratio is much larger for rings and ring-linear blends compared to linear polymers. This confirms the interlocking scenario of rings and their important role in mechanically reinforcing linear matrices. [ABSTRACT FROM AUTHOR]

Nanoparticles reinforce rubbers and enhance Payne effect for the compounds experiencing large amplitude oscillatory shear deformation. Herein the effects of silica and cellulose nanocrystals on the Payne effect of natural rubber compounds are investigated by stress decomposition methods for clarifying the elastic and viscous nonlinearities varying with filler content and composition. The Payne effect is in general characterized by intercycle strain softening and shear thinning behaviors and intracycle hardening and thinning behaviors at high strain (strain rate) amplitudes while the filler influences the behaviors markedly at intermediate strain (rate) amplitudes. Especially, the addition of cellulose nanocrystals in the silica filled compounds improves the elastic nonlinearity and greatly weakens the viscous nonlinearity, providing a perspective on understanding the Payne effect for manufacturing high-performance rubber materials. [ABSTRACT FROM AUTHOR]

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 and a flow viscosity defined in terms of the recoverable strain and the rate of acquisition of unrecoverable strain, respectively. These material functions, based on recoverable and unrecoverable strains (rather than total strain), are defined in the same way independent of the test protocol and provide the viscoelastic properties of a material in a clear and succinct way without requiring a priori knowledge of the constitutive model. At short times, we observe that for a self-assembled wormlike micellar solution, the new material functions exhibit a constant (plateau) modulus and a constant (zero-shear) viscosity independent of the applied shear rate, even under conditions that eventually lead to nonlinear responses. This observation quantitatively corroborates the intuitive picture of material deformation that when the material is close to equilibrium, it responds according to its linear viscoelastic material properties for both linear and nonlinear deformations. The fundamental, universal, and unifying nature of these new transient measures are showing promise in explaining a range of phenomena, including the Payne effect for filled polymers and yield stress materials, as well as suggesting new improved dimensionless groups for more accurate flow diagnosis. This work lays the foundation for measuring material functions that are directly related to the material structure and are agnostic of the testing protocol. [ABSTRACT FROM AUTHOR]

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 both backbone and arm, which are governed by the same evolution equation with different relaxation times. The discrete Baumgaertel–Schausberger–Winter spectrum is adopted for the backbone relaxation. The model has four parameters that are fully determined from the linear spectrum. The equation set is solved analytically by the perturbation method under MAOS and solved numerically under start-up extensional flows. The predictions on the nonlinear rheological behaviors are well consistent with the experiments. [ABSTRACT FROM AUTHOR]

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 of polybutadiene/tetradecane solutions filled with carbon black. Our results show that there is a previously unrecognized transition in the system as the matrix polymer concentration ϕ approaches and passes through a characteristic polymer concentration ϕc. Below ϕc, the system typically shows the classic nonlinearity, where the storage modulus G′ decreases as the strain amplitude γ0 increases and the resulting stress waveforms are distorted from sinusoidal waves. Above ϕc, the system displays an anomalous nonlinearity, where the stress responses at any given strain remain surprisingly sinusoidal regardless of the drop in the storage modulus G′. The critical concentration ϕc is about an order of magnitude greater than the entanglement polymer concentration ϕe. The degree of entanglement in the matrix apparently determines the occurrence of this unusual rheological event and plays a key role here. Increasing the polymer molecular weight enhances this transition. [ABSTRACT FROM AUTHOR]

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, Phys. Fluids 31, 021213 (2019)]. The upper-convected, lower-convected, and corotational Maxwell models are all subsets of the results presented here. The model assumes that the microscale elements causing stress in the material slip compared to the continuum deformation. We introduce a visualization of the nonaffine deformation field that acts on stress-generating elements to reinforce the physical interpretation of the JS/GS class of models. Finally, a case study is presented where previously published results, from fitting TSS models to MAOS data, can be reinterpreted based on the concept of nonaffine motion of the JS/GS framework. [ABSTRACT FROM AUTHOR]

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 miniature melt-mixer at different concentrations. In both cases, as confirmed by TEM investigations, a nanoscopic state of dispersion in the PVDF matrix was achievable using the applied melt mixing procedure. Our results indicated that N-doped nanocomposites, well below their electrical percolation, form a hybrid, load-bearing network structure where network interconnectivity is driven by N-doped CNT domains and near-surface regions of the PVDF phase. This hybrid network formation behavior combined with N-doped CNTs inferior aspect ratio and their higher susceptibility to breakage and length loss during the melt mixing process have led to delayed electrical percolation. In contrast, localized clustering and contact aggregation in a submicrometer scale was the dominant mode of network formation in the undoped CNT/PVDF nanocomposites. These microstructural inferences were further validated in the frame of molecular simulations and optical microscopy investigations. [ABSTRACT FROM AUTHOR]

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We report on the rheology of isotropic and nematic aqueous solutions of a sulfonated all-aromatic polyamide, poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT), that forms high-aspect-ratio rod-like assemblies. For quiescently isotropic solutions, the concentration dependence of the zero-shear viscosity, longest relaxation time, and terminal modulus shows deviations in comparison to the Doi-Edwards theory for hard rods. For quiescently nematic solutions, we characterize the flow behavior through steady-state and transient nonlinear rheological measurements in conjunction with small-angle neutron scattering under shear. The steady-state flow curve is characterized by two anomalous shear thickening responses, one at moderate shear rates and the other immediately prior to flow alignment at high shear rates. We assign the origin of these shear thickening response to director "kayaking" and "out-of-plane steady" states, using predictions from prior high-resolution numerical simulations of sheared nematic rods. Utilizing transient shear flow reversals and step-down experiments, we characterize the oscillatory response of the nematic director through these flow regimes. When the first normal stress difference is plotted versus the shear stress during a transient step-down, the so-called dynamic stress path, the counterclockwise versus clockwise rotation has previously been shown to reveal the relative dominance of viscous versus elastic contributions to the stress tensor, respectively. Our measurements strongly suggest that the anomalous shear thickening behavior in nematic PBDT solutions arises from viscous stresses developed as the ensemble of rods undergoes periodic oscillatory motion under shear, rather than elastic stresses due to broadening of the orientational distribution function. [ABSTRACT FROM AUTHOR]

This study aims to use molecular dynamics (MD) simulations of Kremer–Grest (KG) chains to inform future developments of models of entangled polymer dynamics. We perform nonequilibrium MD simulations, under shear flow, for well‐entangled KG chains. We study chains of 512 and 1000 KG beads, corresponding to 8 and 15 entanglements, respectively. We compute the linear rheological properties from equilibrium simulations of the stress autocorrelation and obtain from these data the tube model parameters. Under nonlinear shear flow, we compute the shear viscosity, the first and second normal stress differences, and chain contour length. For chains of 512 monomers, we obtain agreement with the results of Cao and Likhtman (ACS Macro. Lett. 2015, 4, 1376). We also compare our nonlinear results with the Graham, Likhtman and Milner‐McLeish (GLaMM) model. We identify some systematic disagreement that becomes larger for the longer chains. We made a comparison of the transient shear stress maximum from our simulations, two nonlinear models and experiments on a wide range of melts and solutions, including polystyrene (PS), polybutadiene, and styrene–butadiene rubber. This comparison establishes that the PS melt data show markedly different behavior to all other melts and solutions and KG simulations reproduce the PS data more closely than either the GLaMM or Xie and Schweizer models. We discuss the performance of these models against the data and simulations. Finally, by imposing a rapid reversing flow, we produce a method to extract the recoverable strain from MD simulations, valid for sufficiently entangled monodisperse polymers. We explore how the resulting data can probe the melt state just before the reversing flow. © 2019 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1692–1704 [ABSTRACT FROM AUTHOR]

Dynamic rheological and mechanical properties of seven commercial (xanthan [XG], guar [GG], high methoxylated pectin [HMP], κ‐carrageenan [κ‐Car], agar [AG], alginate [ALG], and carboxymethylcellulose [CMC]) and four emerging hydrocolloids (basil seed gum [BSG], sage seed gum [SSG], Balangu‐Shirazi seed gum [BSSG], and cress seed gum [CSG]) were investigated and the classification of the hydrocolloids were carried out based on them. AG belonged to the first class with 0.81 membership function (MF), κ‐Car and HMP grouped in the second class with 0.68 and 0.71 MFs, respectively, XG, BSG, and SSG were depended to the third class with 0.61–0.70 MFs, finally, CMC, GG, BSSG, ALG, and CSG related to the fourth class, as the most populated class, with MF > 0.61. The first class contained the highest amount of hardness parameter (43.40 ± 2.76 g), the second class included the highest pseudoplasticity parameter (shear‐thinning ratio = −0.54 ± 0.03) and relaxation time (66.25 ± 2.61 s) and the fourth cluster comprised the highest frequency dependency of viscous modulus (exponent of power‐law model for viscous modulus vs. frequency = 0.30 ± 0.05). In addition, the results of this study showed that there was a distinct relationship between nonlinear harmonics in the stress wave and fundamental characteristics of hydrogel networks. The investigation of the rheo‐mechanical properties of biopolymers in large deformation under shear and normal forces can have an important role in the prediction of the behavior of the material in real processes and application conditions, especially in the food industry. Due to the inconvenience of large deformation mechanical tests, such as Weissenberg effect, the complication of the results analyzing and sampling difficulty of semi‐dilute samples; herein, we determined the correlation between large deformation (LAOS and texture analysis) and small deformation (SAOS) tests properties. The studied rheo‐mechanical parameters showed high correlation with the four mentioned network parameters (more than 65% similarity index). Using these results, other scientists could rationally design the experiments and avoid experiments with similar parameters. [ABSTRACT FROM AUTHOR]

In this work, we study the onset of nonlinear rheological behavior of a colloidal dispersion of a synthetic hectorite clay, LAPONITE®, at the critical gel state while undergoing the sol-gel transition. The critical gel state is characterized by a power-law dependence of stress relaxation modulus on time and structurally represents the weakest space spanning percolated fractal network. When subjected to step strain in the nonlinear regime, the relaxation modulus shifts vertically to the lower values such that the deviation from linearity can be accommodated using a strain dependent damping function. We also perform creep-recovery and start-up shear experiments on the studied colloidal dispersion at the critical gel state and monitor deviation in response as the flow becomes nonlinear. A quasilinear integral model is developed with the time–strain separable relaxation modulus to account for the effect of nonlinear deformation. Remarkably, the proposed model predicts the deviation from linearity in the creep-recovery and start-up shear experiments very well, leading to a simple formulation to analyze the onset of nonlinear rheological behavior in the critical gels. We also analyze the energy dissipation during the nonlinear deformation. We show that, for a critical gel, if the onset of nonlinearity happens to be the point of failure, the Boltzmann superposition principle very naturally leads to the Basquin law of failure. [ABSTRACT FROM AUTHOR]

Dynamic oscillatory shear flow has been widely used to investigate viscoelastic material functions. In particular, small amplitude oscillatory shear (SAOS) tests have become the canonical method for characterizing the linear viscoelastic properties of complex fluids based on strong theoretical background and plenty of experimental results. Recently, there has been increasing interest in the use of large amplitude oscillatory shear (LAOS) tests for the characterization of complex fluids. However, it is difficult to define material functions in LAOS regime due to an infinite number of higher harmonic contributions. For this reason, many recent studies have focused on intrinsic nonlinearities obtained in medium amplitude oscillatory shear (MAOS) regime, which is a subdivision of the full LAOS regime. In this study, we reviewed recent experimental and theoretical results of nonlinear material functions in the MAOS regime, which contain four MAOS moduli (two first-harmonic moduli and two third-harmonic moduli) from Fourier and power series of shear stress, and a nonlinear material function Q0 and its elastic and viscous parts from Fourier-transform rheology (FT rheology). Furthermore, to identify linear-to-nonlinear transitions in stress response of model polystyrene (PS) solutions, we presented Pipkin diagrams in frequency ranges from the rubbery plateau region to the terminal region. [ABSTRACT FROM AUTHOR]

This work is concerned with the flow of yield-stress (viscoplastic) fluids through rigid porous media under Stokes flow conditions. The porosity distribution may be periodic, or random and statistically uniform, but not necessarily isotropic. The objective is to make use of an adaptation of the 'variational linear comparison' homogenization method (Ponte Castañeda, 1991) to characterize the nonlinear permeability or mobility for the viscoplastic fluid under macroscopically uniform flow conditions through a given porous medium. The central idea is to express the dissipation-rate potential fully characterizing the mobility of the viscoplastic fluid in terms of an optimization problem for the viscosity of a 'comparison' Newtonian fluid with known permeability defined by its dissipation-rate potential for the same porous medium. Thus, given the porosity and the permeability tensor for the flow of a Newtonian fluid through a generally anisotropic porous medium with given microstructure, the method provides a bound for the corresponding mobility tensor of the viscoplastic fluid. Applications of the method are given for special types of generalized Newtonian fluids, including Herschel–Bulkley and Carreau fluids, by making use of known estimates for the permeability of Newtonian fluids, including the Blake–Carman–Kozeny formula and Weissberg–Prager bounds for isotropic random porous media, as well as numerical and asymptotic estimates for anisotropic periodic fibrous microstructures. The main advantages of the method are its generality and simplicity. • Analytical models for the flow of yield stress fluids through porous media • Models based on the author's variational linear comparison homogenization technique • Yield stress fluid mobility in terms of permeability of comparison Newtonian fluid • Lower/upper bounds for the mobility for shear thinning/thickening fluid behavior • Applications to Herschel–Bulkley fluid and isotropic and anisotropic porous media [ABSTRACT FROM AUTHOR]

Nonlinear rheology can be used to monitor the molecular chain movement of polymer materials under large strain conditions. In this work, we firstly set up large amplitude oscillatory shear (LAOS) conditions simulating the hot-extrusion 3D printing (HE-3DP) process and attempted to match the structural formation of wheat starch (WS) by starch-oleic acid (OA)-chlorogenic acid (CA) interactions during HE-3DP from perspectives of nonlinear rheology. Results showed that when compared with WS system, the b value and zero-strain nonlinearity (Q 0) of WS-OA system increased with OA addition, and it exhibited obvious strain hardening and shear thinning behaviors, which were ascribed to that OA interacted with starch to form single helix and V-type crystalline structure through hydrophobic force, and it obstructed the integrality of gel network. For WS-CA system, the b value and Q 0 decreased with CA addition and the shear thickening behavior was increased which could be explained that CA interacted with starch chains through hydrogen bonding following the formation of aggregates structure, thus improving the integrity of network structure. Notably, when compared to above two binary systems, the early emergence of strain thickening and the weakening of strain stiffening for WS-OA-CA system declared that CA contributed to inhibiting the aggregation and assembly of the single helix formed by WS-OA interactions. Overall, this study provided important information for the application of nonlinear rheology in the structure evolution of starch system during HE-3DP. [Display omitted] • Nonlinear rheology was used to exploring the structural formation in the HE-3DP. • 3DP-WS-OA had obvious strain hardening and strain thinning behaviors. • CA improved shear thickening and strain stiffening through hydrogen bonding. • CA was inclined to interact with single helix structure in the 3DP-WS-OA-CA. [ABSTRACT FROM AUTHOR]

First-harmonic MAOS moduli were demonstrated experimentally using monodisperse linear polystyrene (PS) solutions at different concentrations. Two first-harmonic intrinsic nonlinearities are asymptotic deviations from two linear viscoelastic moduli and obtained in medium amplitude oscillatory shear (MAOS) regime. Master curves of first-harmonic MAOS moduli for PS solutions provided novel information which has never been reported before. The interrelationship between first-harmonic and third-harmonic MAOS moduli was evaluated at low and high De. At the low-De limit, all solutions followed the universal interrelation predicted by fourth-order fluid expansion. At the high-De limit, where no universal interrelation exists, the average first-harmonic to third-harmonic elastic MAOS moduli ratio was −22.26, and for viscous counterparts, the magnitude and sign of this ratio changed on increasing frequency. Unentangled and entangled solutions were distinguished using normalized viscous moduli at De > 1. Viscous MAOS moduli normalized by SAOS complex modulus displayed a plateau for unentangled solutions and a decreasing behavior for entangled solutions. First-harmonic MAOS moduli of entangled solutions agreed well with multimode molecular stress function (MSF) predictions under the all relaxation mode assumption, which contrasted with third-harmonic MAOS predictions using the terminal relaxation mode assumption. It is expected that the first-harmonic MAOS results in this paper will be good reference information for future MAOS studies and computer simulations. [ABSTRACT FROM AUTHOR]

While there has been much success in modeling the linear and nonlinear rheology of monodisperse entangled linear polymers, progress in the constitutive modeling of polymeric materials continues to lag behind the needs of industry. Industrially sourced polymers are typically polydisperse (comprising a broad distribution of molecular weights), making their rheology more suitable for processing but also more difficult to predict. To date, there are no molecular-based constitutive models that are practically suitable for describing industrially relevant polymers in industrially relevant flows. In this article, we extend but strongly simplify the model of Read et al. [J. Rheol. 56, 823–873 (2012)], which is able to predict the linear and nonlinear rheology of bidisperse blends but is prohibitively complex for industrial use. We propose a pair of simplified tube models for polydisperse melts of entangled linear polymers that combine the success of the double reptation approximation [des Cloizeaux, Europhys. Lett. 5, 437–442 (1988)] in the linear regime with the success of the Rolie-Poly constitutive equation [Likhtman et al., J. Non Newtonian Fluid Mech. 114, 1–12 (2003)] in the nonlinear regime. We first review the key concepts of the double reptation approximation and the original (monodisperse) Rolie-Poly constitutive model. Subsequently, we provide the details of our approximate models for the particular case of a bidisperse blend and show that these models naturally identify the effects from couplings between constraint release and chain retraction (i.e., the so-called "enhanced stretch relaxation time"). Finally, we generalize to a multicomponent (polydisperse) model, based on the same underlying principles. Along the way, we also show that both of our models are in qualitative, and largely quantitative, agreement with experimental data for bidisperse and polydisperse melts of entangled linear polymers. [ABSTRACT FROM AUTHOR]

In this work, doughs made with gluten add chickpea composite flour were mixed to reach the 500BU standard and baked into bread products. Chickpea flour was substituted at the level of 20%, 30%, and 40% by wheat gluten to provide structural support for the dough. Higher gluten concentrations improved gas bubble retention as determined by crumb image analysis, resulting in higher final loaf volume. Dough samples were taken out of the fermentation chamber at 0, 30, 60, and 90 min to study the effect of fermentation on rheology. Utilizing SPP deltoids (G t ′ vs G t ″ plot), the intracycle and intercycle network rearrangement of dough were studied in details. Obtaining deltoids as a function of fermentation time offers an insight into the impact of fermentation on dough structure. It is found that longer fermentation time makes gluten-chickpea composite dough more elastic in the linear region (<1% strain) and less elastic in the nonlinear region. This work helps to demonstrate an application of SPP analysis in facilitating the development of innovative bread products made with a mixture of pulse flour and wheat gluten. • Composite breads were baked from chickpea flour mixed with gluten. • Non-linear rheological properties offered insights into dough development. • Increasing gluten content restricts deltoid expansion. [ABSTRACT FROM AUTHOR]

In this paper, the authors discuss the results of research on the preparation and properties of superabsorbent hydrogels based on carboxymethylated high-amylose corn starches. They were obtained by graft copolymerisation (in an aqueous environment) of acrylic acid and its sodium salt onto modified starches (with various substitution degrees DS = 0.2 and 0.8), using potassium persulfate as an initiator and N,N’-methylenebisacrylamide (MBA) as a cross-linker. Modified starches, with various DS, were used to synthesise two series of hydrogels with varying molar ratios of cross-linkers to monomers. The swelling behaviour of hydrogels was studied and their properties were estimated using the kinetic equation. The occurrence of starch–polyacrylic acid covalent interactions was demonstrated by FTIR analysis. Nonlinear rheological methods have proved to be very effective in assessing the mechanical properties of hydrogels. LAOS (large -amplitude oscillatory shear) analysis allowed the determination of the durability of the gel structure as a function of the amount of absorbed water.

This study seeks to unravel the effect of carbon nanotube’s physical and chemical features on the final electrical and rheological properties of polymer nanocomposites thereof. Nitrogen-doped carbon nanotubes (N-CNTs) were synthesized over two different types of catalysts, i.e., Fe and Ni, employing chemical vapor deposition. Utilizing this technique, we were able to synthesize N-CNTs with significantly different structures. As a result, remarkable differences in the network structure of the nanotubes were observed upon mixing the N-CNTs in a polyvinylidene fluoride (PVDF) matrix, which, in turn, led to drastically different electrical and rheological properties. For instance, no enhancement in the electrical conductivity of poorly-dispersed (N-CNT)Ni/PVDF samples was observed even at high nanotube concentrations, whereas (N-CNT)Fe/PVDF nanocomposites exhibited an insulative behavior at 1.0 wt%, a semi-conductive behavior at 2.0 wt%, and a conductive behavior at 2.7 wt%. In terms of rheology, the most substantial differences in the viscoelastic behavior of the systems were distinguishable in the medium amplitude oscillatory shear (MAOS) region. The stress decomposition method combined with the evaluation of the elastic and viscous third-order Chebyshev coefficients revealed a strong intra-cycle elastic nonlinearity in the MAOS region for the poorly-dispersed systems in small frequencies; however, the well-dispersed systems showed no intra-cycle nonlinearity in the MAOS region. It was shown that the MAOS elastic nonlinearity of poorly-dispersed systems stems from the confinement of N-CNT domains between the rheometer’s plates for small gap sizes comparable with the size of the agglomerates. Moreover, the intra-cycle elastic nonlinearity of poorly-dispersed systems is frequency-dependent and vanished at higher frequencies. The correlation between the microstructure and viscoelastic properties under large shear deformations provides further guidance for the fabrication of high-performance 3D-printed electrically conductive nanocomposites with precisely controllable final properties for engineering applications.