Nonlinear Rheological Behavior Research Articles

Co-vulcanization of natural rubber and Eucommia ulmoides gum for mediation of the nonlinear rheology behaviors

Co-vulcanization of natural rubber (NR) and high-moduli Eucommia ulmoides gum (EUG) is promising while the reduction in crystallinity of crosslinked EUG is adverse for developing high-performance materials. Proposed herein is a novel method to prepare high-strength and high-stretchability NR/EUG vulcanizates with rapid vulcanization of EUG into slightly crosslinked particles, followed by further vulcanization of NR to form crosslinked matrix network. Deep eutectic solvents (DESs) are employed to facilitate the vulcanization of EUG during its blending with NR. The two-step vulcanization results in vulcanizates exhibiting superior mechanical properties under shear, tensile, and compressive conditions, significantly exceeding those of vulcanizates prepared by traditional processing methods. The reinforcement mechanism is elucidated by controlling thermomechanical coupling conditions and is supported by comprehensive structural characterizations. It is suggested that the EUG crystalline regions, maintained through the special processing method, work in conjunction with the stress-induced crystallization of the matrix to enhance the vulcanizates, nearly doubling the deformation stress at 800% strain. The crystalline regions can mediate the deformation stress during shear and compression and weaken nonlinear rheological behavior. The established structure-performance relationship is guidable for preparing high-performance NR/EUG blend vulcanizates.

Exploring the physicochemical and rheological properties of sustainable asphalt binders modified with lignin and high-viscosity additive

The primary objective of this investigation is to evaluate how the incorporation of lignin and high-viscosity modifiers impacts the performance of asphalt binders. Lignin-modified asphalt binder (LBA) and lignin-high viscosity modifier composite-modified asphalt binder (LHA) were created by blending 5 % and 15 % lignin, respectively. To understand the physicochemical interactions, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) were employed to analyze functional groups, thermal properties, and phase changes. Additionally, the linear rheological behavior and nonlinear rheological behavior were evaluated through frequency sweep and multiple stress creep recovery tests. The findings suggest that lignin blends physically with the asphalt binder and high-viscosity modifier without a chemical reaction. Although the onset pyrolysis temperature of lignin is significantly lower than that of asphalt binders, due to its relatively low content, the thermal decomposition of lignin-modified asphalt binders is primarily controlled by the asphalt binder itself and still exceeds the construction temperature. However, lignin incorporation increases the asphalt binder's glass transition temperature, potentially affecting low-temperature performance. Lignin significantly enhances the modulus in the high-frequency region of both unmodified and high-viscosity modified asphalt binder. However, it has a negative effect on the modulus in the low-frequency region of high-viscosity modified asphalt binder. Furthermore, nonlinear creep recovery test results demonstrate that lignin positively contributes to the deformation resistance of unmodified asphalt binder in a content-dependent manner, whereas it reduces the elastic behavior and deformation resistance of high-viscosity modified asphalt binder. In addition, low levels of lignin increase the stress sensitivity of binders, while high levels of lignin decrease it. Despite these effects, the performance of lignin and high-viscosity additive composite-modified asphalt binder remains superior to that of unmodified asphalt binder. These findings offer valuable insights into the combined use of lignin and polymers in asphalt binder modification.

Nonlinear rheological behavior of glass-forming colloidal suspensions under oscillatory shear: Experiment and relation to mode coupling theory predictions

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 (I3/1=I3/I1) and within the intrinsic nonlinearity framework of the Q-parameter (Q0=limγ0→0⁡(I3/1/γ02)). 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, I3/1 shows an unusual scaling of I3/1∝γ04 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 Q0 to be maximal in the region of the α-relaxation for colloidal liquids. The colloidal glasses do not exhibit a maximum in Q0, but an increase in Q0 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.

Non-linear rheological behaviors of polyvinyl alcohol/silver nanowire/silica nanoparticle suspensions under large amplitude oscillatory shear flows

Non-linear rheological behaviors of polyvinyl alcohol/silver nanowire/silica nanoparticle suspensions under large amplitude oscillatory shear flows

Impact of Deformability and Rigidity of Starch Granules on Linear and Non-Linear Rheological Behavior of Waxy Rice Starch Gels and Applicability for Food End Uses.

The objective of this study was to investigate granule size and distribution and deformability of granules and their effect on the rheological properties of waxy starch gels. Native (granular) waxy rice gels (10%) were prepared, and their response in oscillatory shear was investigated in the linear and non-linear viscoelastic regime. The results show the gels were mainly composed of aggregated and deformed swollen granules. Significance of granule size and its distribution, deformability of granules, and the molecular characteristics of amylopectin (AP) on storage modulus of those gels was demonstrated. A low degree of deformability of granules, typical for small granules with a broad size distribution and small molecular size of AP with short external chains, resulted in rigid and brittle gels. Highly deformed granules and high AP leachates, however, yielded soft gels. It was found that the transition of elastic to plastic behavior in the non-linear regime (LAOS) was gradual when AP had long external chains, but an abrupt transition was observed with the gel with short exterior chains of AP. Differences in rheological properties of cohesive waxy starch gels appear to be mainly impacted by the varying degrees of granule deformability and rigidity, which is further attributed to a combination of factors, including granule size, particle size distribution, molecular size, the external chain length of amylopectin (AP), and lipid content. The significance of this study is that it will assist the food industry in selecting suitable waxy rice starches to gain desired textural properties of end products.

Unexpected Stress Overshoot in Extensional Flow of Star Polymer Melts.

Previous studies have shown that the nonlinear rheological behavior of 3-arm star polymer melts in fast extensional flow is identical to that of linear polymers with the same span molecular weight, because the star polymers are highly aligned and have a similar conformation as the corresponding linear polymers. However, with more arms, it would be more difficult for the stars to be aligned like linear chains, and the nonlinear extensional rheology of star polymers with more arms under large deformations has not been investigated yet. Here we show that the star polystyrene (8-10 arms) melts behave differently from the linear polystyrenes. A transient stress overshoot is observed in the fast extensional flow, probably due to the difference in entanglement density near and far away from the branch point.

Biopolymer networks packed with microgels combine strain stiffening and shape programmability

Biomaterials that can be reversibly stiffened and shaped could be useful in broad biomedical applications where form-fitting scaffolds are needed. Here we investigate the combination of strong non-linear elasticity in biopolymer networks with the reconfigurability of packed hydrogel particles within a composite biomaterial. By packing microgels into collagen-1 networks and characterizing their linear and non-linear material properties, we empirically determine a scaling relationship that describes the synergistic dependence of the material's linear elastic shear modulus on the concentration of both components. We perform high-strain rheological tests and find that the materials strain stiffen and also exhibit a form of programmability, where no applied stress is required to maintain stiffened states of deformation after large strains are applied. We demonstrate that this non-linear rheological behavior can be used to shape samples that do not spontaneously relax large-scale bends, holding their deformed shapes for days. Detailed analysis of the frequency-dependent rheology reveals an unexpected connection to the rheology of living cells, where models of soft glasses capture their low-frequency behaviors and polymer elasticity models capture their high-frequency behaviors.

Nonlinear oscillatory rheology of aqueous suspensions of cellulose nanocrystals and nanofibrils

In this work, the nonlinear rheological behavior of aqueous suspensions composed of two typical nanocellulose [rod-like cellulose nanocrystals (CNCs) and filamentous cellulose nanofibrils (CNFs)] was examined and compared by using various large-amplitude oscillatory shear (LAOS) analysis methods, such as Fourier-transform rheology, stress decomposition, Chebyshev polynomials, and the sequence of physical processes. From our analysis, the nonlinear rheological parameters of higher harmonics, dissipation ratio, strain hardening ratio, shear thickening ratio, transient modulus, and cage modulus were obtained and quantitatively analyzed. CNCs tend to assemble to form anisotropic structures in an aqueous medium while the CNFs are entangled to form gels. The CNF suspensions demonstrated a significant viscous modulus overshoot and had stronger yield stresses, but the yield of CNC suspensions was more ductile. In the case of low concentrations, the CNF suspensions demonstrated stronger intracycle shear thickening behavior in medium-amplitude oscillatory shear region and lower dissipation ratios at small strain amplitudes. Although both nanocellulose suspensions revealed the existence of four intracycle rheological transition processes (viscoplastic deformation, structural recovery, early-stage yielding, and late-stage yielding), the CNF suspensions exhibited a stronger structural recovery ability. Larger strain amplitudes did not invariably result in a broader range of intracycle rheological transitions, which are also affected by the excitation frequency. The application of the various LAOS analysis methods provided valuable intracycle nonlinear rheological insights into nanocellulose suspensions, which are of great importance for enhancing their industrial perspectives.

Highly distinctive linear and nonlinear rheological behaviors of mucin-based protein solutions as simulated normal and asthmatic human airway mucus

Mucus on the human airway surface normally provides a fluid barrier to trap and remove inhaled hazardous particulates such as viruses and bacteria, a physiological function known as mucus clearance. This function, however, can fail if the mucus has abnormal rheological properties, as in the case of certain lung diseases such as asthma. Despite its importance, airway mucus rheology has not been well studied so far, largely because of its complex nature and limited availability. Therefore, in this study, we prepared mucin-based protein solutions as simulated normal and asthmatic airway mucus (NM and AM, respectively) and subsequently studied them in both linear and nonlinear rheological conditions using either conventional steady-state or large amplitude oscillatory shear experiments together with nonlinear multi-mode Giesekus model analysis. We also examined the microscopic structure of the simulated airway mucus by optical or atomic force microscopy. We found that both NM and AM exhibited typical nonlinear rheological behaviors of protein solutions. However, as compared to NM, AM was much more solid-like, and the viscosity, yield stress, and dynamic modulus were more than ten times that of NM. These differences in macroscopic rheological behaviors between NM and AM could be attributed to their different microstructures. Taken together, this study provides evidence that airway mucus may dramatically change its rheological behaviors with changing chemical composition and microstructure as occurring in diseased conditions such as AM. Thus, the presented rheological assessment and modeling analysis, together with the microscopic characterization of simulated airway mucus, may have important values for better understanding the critical roles of mucus rheology in the determination of the mucus clearance function in health and disease as well as the development of pulmonary drug delivery systems.

Discontinuous Shear Thickening in Biological Tissue Rheology.

During embryonic morphogenesis, tissues undergo dramatic deformations in order to form functional organs. Similarly, in adult animals, living cells and tissues are continually subjected to forces and deformations. Therefore, the success of embryonic development and the proper maintenance of physiological functions rely on the ability of cells to withstand mechanical stresses as well as their ability to flow in a collective manner. During these events, mechanical perturbations can originate from active processes at the single-cell level, competing with external stresses exerted by surrounding tissues and organs. However, the study of tissue mechanics has been somewhat limited to either the response to external forces or to intrinsic ones. In this work, we use an active vertex model of a 2D confluent tissue to study the interplay of external deformations that are applied globally to a tissue with internal active stresses that arise locally at the cellular level due to cell motility. We elucidate, in particular, the way in which this interplay between globally external and locally internal active driving determines the emergent mechanical properties of the tissue as a whole. For a tissue in the vicinity of a solid-fluid jamming or unjamming transition, we uncover a host of fascinating rheological phenomena, including yielding, shear thinning, continuous shear thickening, and discontinuous shear thickening. These model predictions provide a framework for understanding the recently observed nonlinear rheological behaviors in vivo.

Modeling linear and nonlinear rheology of industrial incompatible polymer blends

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.

Effect of protein concentration on the structural, functional properties, linear and nonlinear rheological behaviors of thermally induced hemp protein gels

Effect of protein concentration on the structural, functional properties, linear and nonlinear rheological behaviors of thermally induced hemp protein gels

External factors affecting the linear and nonlinear rheological behavior of oleogel-based emulsions

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.

Geocolloidal interactions and relaxation dynamics under nanoconfinement: Effects of salinity and particle concentration

HypothesisEnergy-related contaminants are frequently associated with geocolloids that translocate in underground fissures with dimensions comparable with geocolloids. To assess the transport and impact of energy-related contaminants in geological systems, fundamental understandings of interfacial behaviors of nanoparticles under confinement is imperative. We hypothesize that the dynamic properties of geocolloids, as well as their dependence on aqueous medium conditions would deviate from bulk behaviors under nanoconfinement. ExperimentsForce profiles and rheological properties of 50 nm silica nanoparticles in aqueous media confined between mica surfaces as a function of surface separation, particle concentrations, and salinity were measured utilizing the surface forces apparatus. FindingsForce profiles revealed the critical surface separation for nonlinear rheological behaviors coincides with the onset of exponential repulsion between mica surfaces. When salts were absent, the normal forces and viscosity values of colloidal suspensions resembled pure water. In contrast, with salts, the force profiles and corresponding critical length scales were found to be highly sensitive to the particle concentration and the degree of confinement. A Newtonian to shear-thinning transition was captured with increasing degrees of confinement. Our results show that the interplay among confinement, particle, and ionic concentrations can alter the interparticle forces and rheological responses of true nanosized-colloidal suspensions and thus their transport behaviors under nanoconfinement for the first time.

Effect of deep eutectic solvents on vulcanization and rheological behaviors of rubber vulcanizates

Deep eutectic solvents (DESs) are able to promote vulcanization of rubbers while the mechanisms remain unclear. Herein 4-methyl-5,7-dihydroxycoumarin (DHMC) as hydrogen bond donor (HBD) was used to synthesize DES by reaction with tetrabutylammonium bromide (TBAB) as hydrogen bond acceptor (HBA). The effects of DHMC, TBAB and DES on vulcanization of natural rubber (NR) and isoprene rubber (IR) were studied. It is shown that DES could participate in crosslinking network and adjust crosslinking density (vc) of the vulcanizates through physical and chemical interactions with NR non-rubber components, zinc oxide (ZnO) activator and N-cyclohexyl-2-benzothiazolesulfenamide (CZ) accelerator. Furthermore, DES influences linear and nonlinear rheological responses and mechanical behaviors of NR vulcanizates. The NR vulcanizates cured at 120 °C with 0.1–0.3 phr (part per hundred parts of rubber) DES exhibit higher tensile strengths and lower vc in comparison with the control one cured at 140 °C, which is assigned to the more homogenous crosslinking network in the former. This work provides an effective way to modulate the crosslinking network to produce high-strength vulcanizates at lowered vulcanization temperatures and ZnO amount, which is beneficial for the preparation of rubber products with high strengths and low hysteresis energies.

A critical study of the nonlinear rheological properties in major classes of foods using the Sequence of Physical Processes (SPP) method and the Fourier Transform Coupled with Chebyshev Decomposition (FTC) method

The nonlinear rheological behaviors of three different classes of foods (emulsion, suspension, and elastic network) were studied and analyzed using the Rogers Sequence of Physical Processes (SPP) method and the Ewoldt-McKinley method of coupling Fourier Transform with Chebyshev Decomposition (FTC). SPP analysis led to instantaneous rheological parameters G′t and G″t at any point in time, providing a more accurate picture of the linear viscoelastic region and crossover points by the 3D amplitude sweep. When G′t is plotted against G″t, the resulting graph is a deltoid which offers a detailed and distinctive intracycle behavior of each class of food. Analyzing the revolution of deltoids with increasing strain allows for the determination of a critical strain, beyond which irreversible network breakdown occurs. The strain range between the linear viscoelastic limit and the critical strain found in SPP is comparable to the MAOS region as determined with FTC. Under increasing amplitude, predominantly elastic networks showed a gradual structural rearrangement, while more erratic and abrupt changes were observed in the suspension and emulsion we studied. Under increasing frequency, elastic responses dominate viscous responses in all samples due to the shorter experimental time, allowing less relaxation.

The linear/nonlinear rheological behaviors of Pickering emulsion stabilized by Zein and Xanthan gum: Effect of interfacial assembly strategies

Protein/polysaccharide complexes have been widely used to fabricate Pickering emulsions, yet their linear and nonlinear rheological behaviors have received little attention. In this work, two interfacial assembly strategies of layer-by-layer (LBL) and directly mixed (DM) were employed to create zein (2%, 1%, w/v)/xanthan gum (XG) (0.8%, 0.4%, 0.2%, w/v) complex Pickering emulsions (oil phase: aqueous phase = 1:2). Both small amplitude oscillatory shear (SAOS) and large amplitude oscillatory shear (LAOS) behaviors were investigated. Results showed that regardless of interfacial assembly strategies, emulsions exhibited relatively smaller droplet size, but had higher viscosity and storage modulus (SAOS test) with XG concentrations at 0.8% (w/v). The steady shear test showed LBL emulsions had superior viscosity, with a minor difference between DM and LBL emulsions in the linear SAOS test. Both interfacial assembly strategies resulted in emulsions exhibiting a hysteresis loop and a thixotropic recovery rate above 85%. The Elastic/Viscous Lissajous plots revealed that the elasticity and stiffness were affected by interfacial assembly strategies. LBL emulsions showed a more pronounced secondary loop, accompanied by a greater thixotropic restructuring time scale. The micromorphology contributed to the diverse linear and nonlinear behaviors, with the zein-XG complex mixed layer coating the oil droplets in DM emulsions and XG being added to a previously zein-emulsified emulsion to form a multilayer in LBL emulsions. In addition, emulsions showed a well-distributed nature, with no oil-off phenomena observed during centrifugal, salt, and thermal treatments. Results illustrated the effect of interfacial assembly strategies on the linear/nonlinear rheological behavior of Pickering emulsion. Our study might be helpful in preparing Pickering emulsion as edible ink for 3D printing and as a fat replacer.

Simulation and experimental study of ultrasonic-assisted shear thickening polishing of cemented carbide

In order to obtain a good surface quality of carbide inserts, an ultrasonic-assisted shear thickening polishing (UASTP) method is proposed in this paper. Using the shear thickening property of non-Newtonian fluids and combining with the principle of ultrasonic vibration, the abrasive grains wrapped by the polishing slurry carry out both flexible micro-cutting and high-frequency micro-collision on the material surface. This enables more efficient polishing of the microscopic surface of the material. In this paper, the polishing principle of this method is analyzed. The rheological characteristics of shear thickening polishing slurry are studied, and a continuity model that can adapt to nonlinear rheological behavior is proposed based on the Gross constitutive equation. The effects of fluid velocity, ultrasonic amplitude and ultrasonic frequency on polishing speed and polishing pressure in the Preston equation are studied by COMSOL Multiphysics simulation software. This method's material removal rate model is established based on the high-frequency periodic characteristics of ultrasonic action, combining the simulation results with polishing experiments, which accurately describe the variation law of material removal rate with polishing time. After polishing the carbide insert for 60 min with this method, a smooth surface is obtained with continuous surface ripple measurements and small floating values; the surface roughness is reduced from 195 nm to 16.1 nm with an improvement rate of 91.7 %, and the material removal rate reached 0.71 μm/h, which improved the surface roughness improvement rate and material removal rate by 27.6 % and 44.9 %, respectively, compared with the STP method. The experimental results show that the UASTP method is an efficient composite polishing technology to enhance the cemented carbide's surface quality further.

The “solvent” effect of short arms on linear and nonlinear shear rheology of entangled asymmetric star polymers

This study examines the influence of the short arms in model asymmetric 3-arm star polymers, in which the short arm is unentangled while the other two long arms are entangled, on linear and nonlinear shear rheological behavior. As increasing the short arm length of the asymmetric star polymers, the linear viscoelastic rubber plateau decreases, indicating the relaxed short arms act as “solvent” that dilute the star polymers. This idea is examined by the relationship between the plateau moduli of polymer solutions GN(φ) and the corresponding polymer melts GN(1) for entangled linear polymers, GN(φ) = GN(1)φ1+α, where φ is the volume fraction of the polymer. The “solvent” effect of the short arms is also supported by the nonlinear rheology results showing weaker damping function and larger peak strain at stress overshoot. With the above clarification of the short-arm contributions, this work provides a guidance of molecular design for tuning linear and nonlinear rheology of star polymers.

An investigation into the nonlinear rheological behavior of modified asphalt binders using large amplitude oscillatory shear rheology

ABSTRACT Asphalt binders have been studied extensively with respect to their linear viscoelastic properties. From these properties, performance metrics have been derived and used for specification purposes. However, these materials are used in asphalt concrete pavements where they may experience time-dependent loads in the nonlinear regime. In the past, the vast majority of asphalt binders exhibited strong correlations between their linear and nonlinear properties and so despite this mismatch in characterization and the actual use phase domains, a system based on linear properties could be reliably deployed. More recently though, novel binders and additives have been introduced with differing relationships between linear and nonlinear behaviors. As such there is a need to characterize the asphalt binder response under large strains and use specifications that more explicitly account for the binder nonlinearity. Here, an attempt has been made to characterize the nonlinear rheological properties of asphalt binder using large amplitude oscillatory shear. The response of a single terminal blend, crumb rubber modified binder under large strains is analyzed using Lissajous-Bowditch plots while the contribution of higher harmonics is evaluated using Fourier-transform rheology. Finally, the elastic and viscous contributions are obtained using stress decomposition to an orthogonal set of Chebyshev polynomials. It is found that the relative nonlinearity increases with increasing strain and frequency under the tested conditions. The asphalt binder evaluated in this study predominantly exhibits shear thinning and either strain stiffening or softening behavior depending upon the test conditions. The applicability of time-temperature superposition in the nonlinear regime for asphalt binders is also evaluated.