Large Amplitude Oscillatory Shear Deformation Research Articles

Effects of Mixing and Large-Amplitude Oscillatory Shear Deformations on Microstructural Properties of Gliadin and Glutenin as Captured by Stop-Flow Frequency Sweeps in Small-Amplitude Oscillatory Shear.

Gliadin and glutenin extracted from vital wheat gluten were studied using Large Amplitude Oscillatory Shear (LAOS) followed by stop-flow frequency sweep tests after being subjected to short (4 min) and prolonged (60 min) mixing times. The LAOS tests were conducted at up to two different strain amplitudes (γ: 0.1%, 200%; ω: 10 rad/s) to apply small and large deformations to the gliadin and glutenin after mixing for different time periods. Frequency sweep tests (ω: 0.01-100 rad/s, γ: 0.06%) revealed an increase in the elasticity of gliadin with respect to an increasing mixing time, as evidenced by a robust increase in G'(ω), coupled with a less robust increase in G″(ω). Consistent with the increase in elasticity, a progressively lower tanδ(ω) and G'(ω) slope were observed for the gliadin that underwent 60 min of mixing followed by large LAOS deformations. However, G'(ω), G″(ω), and η*(ω) remained constant for glutenin as the mixing time increased. Elastic decay with an increase in tanδ(ω) was found for glutenin when subjected to prolonged mixing followed by large LAOS deformations, which became apparent at high frequencies. The stop-flow LAOS (non-linear region)-frequency sweep (linear region) tests provided an understanding of how exposure to different mixing times and LAOS deformations of different magnitudes influence the mechanical/rheological properties of the main gluten proteins.

Covalently cross‐linked hydrogels: Mechanisms of nonlinear viscoelasticity

AbstractGelatin‐based hydrogels have been widely used in tissue engineering, three‐dimensional cell culture, drug delivery, and cell therapy. The mechanical behaviour of hydrogels combined with their chemical properties determines their functionality and efficacy. With respect to the mechanical behaviour of hydrogels, the vast majority of publications have reported their linear viscoelastic response. However, for practical conditions in the body, these materials experience large deformations beyond the linear viscoelastic limit. Herein, to mimic practical conditions and to evaluate the mechanical response of the hydrogels subjected to large deformations, we report inter‐ and intra‐cycle nonlinear viscoelastic behaviour of a gelatin methacryloyl (GelMA) hydrogel with different concentrations of the hydrogel precursor (10%–20% [w/v]) under large amplitude oscillatory shear deformation. To achieve this, we used a novel technique by chemically bonding the hydrogels to treated glass slides, which were attached to the oscillating metal plates using a double‐sided tape to alleviate any error arising from wall slip during rheological measurements. The results show that the elasticity of the covalently cross‐linked hydrogels at large deformations obeys a nonlinear force‐extension law and that the viscous intra‐cycle nonlinearity at moderate deformations stems from the dual cross‐linked (DC; i.e., physical and chemical) nature of the GelMA hydrogel. It was also shown that viscoelastic parameters can be tuned by the concentration of the hydrogel precursor, that is, yield stress increased from 2.6–7.1 kPa, critical strain amplitude decreased from γ0 = 100%–70%, and the onset of inter‐cycle nonlinearity shifted from γ0 = 50%–20% upon increasing the concentration of the hydrogel precursor. These insights have important implications for the rational development of hydrogel‐based biomaterials to design biocompatible scaffolds in tissue engineering applications.

Large amplitude oscillatory rheology of silica and cellulose nanocrystals filled natural rubber compounds

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.

Small and large oscillatory shear properties of concentrated proteins

A closed cavity rheometer was employed to assess the properties of concentrated protein materials before, during and after thermal treatment, using conditions that are relevant to the production of meat analogues. Pea and soy protein isolate and wheat gluten were used as model matrices. The analysis was done using Lissajous curves, both for small and large amplitude oscillatory shear deformation. The energy dissipation ratios based on the enclosed area inside the Lissajous curves characterize the plasticity of the materials. The results show that the modulus of wheat gluten increases during heating and remains elevated after cooling. In contrast, the moduli of pea and soy protein isolates decrease during heating. Subsequent cooling leads to properties that are similar to the rheological properties of unheated pea and soy protein isolates. Lissajous curves and energy dissipation ratios provide insight in the non-linear response. At 30 °C, pea and soy protein isolate have a higher dissipation ratio than wheat gluten. Upon a heat treatment and even after cooling, the dissipation ratio was smaller at similar strain amplitude compared with 30 °C. This indicates that heating induced more elasticity. Upon heating, pea protein isolate loses its elastic properties faster than soy protein isolate, while wheat gluten showed abrupt dissipation after extensive deformation. The observed characteristics are consistent with the behaviour during extrusion and shearing, in which wheat gluten forms extended filaments, while soy and pea protein isolates form a homogeneous matrix. Studying the large oscillatory shear behaviour during and after thermal treatment provides a more detailed picture of the rheological changes during processing, than one would obtain through classical rheology. The dissipation ratio summarizes the information in the Lissajous curves. These insights help to better identify material-structure-process relationships for concentrated plant protein materials during thermomechanical conversions, such as extrusion.

Effects of Bloom number on phase transition of gelatin determined by means of rheological characterization

This study shows the impact of the Bloom number on the melting and gelation behavior of porcine gelatin. Different batches of gelatin were prepared in concentrations of 2, 3, and 5 wt% having Bloom numbers of 100, 180, 240, and 260. Using asymmetrical flow field-flow-fractionation, the molecular weight of gelatin was determined. It was observed that higher Bloom numbers correspond to higher molecular weights. Systematic strain and temperature sweep tests were conducted to determine the yielding point and the phase transition temperatures. The latter was established by the crossover point method and the Winter-Chambon criterion, and small differences between these two methods were recorded. By increasing the Bloom number, the dynamic moduli were increased, as well as the gelation and melting temperatures. The same trend is valid for the gelatin concentration. On the other hand, the Bloom number does not considerably affect the yielding phenomenon under large amplitude oscillatory shear deformations. In conclusion, the Bloom number has a similar rheological effect on gelatin as the molecular weight, and considerable alterations of the viscoelastic gel properties can be expected at significantly different Bloom numbers.

Mechanical response of industrial benchmark lipsticks under large-scale deformations

This work documents the first account of advanced mechanical properties of six commercial lipsticks, some of which serve as market leads. We systematically studied their nonlinear viscoelastic properties under large amplitude oscillatory shear deformations. At large strains, all lipsticks showed intercycle strain softening, the extent of which initially depended on the prototype in the nonlinear regime. This behavior, markedly, was absent after the crossover of the dynamic moduli. Parameters obtained from the strain amplitude sweeps, i.e., the intrinsic elastic modulus and the stress maximum, demonstrated distinct prototype dependence. The Lissajous plots and the dimensionless nonlinear indices were determined using the MITlaos software. They showed intracycle elastic strain stiffening and viscous shear thinning. The angular oscillation frequency directly influenced the linear viscoelastic measures of all the benchmark lipsticks, and the nonlinear properties of only a few benchmark ones. The current study generates standard nonlinear rheology data that can be associated with the lipstick sensory attributes and typical tribological parameters. This may serve as an effective way to examine the transition from the initial spreading to the post-application sensation.

Nonlinear viscoelastic properties of native male human skin and in vitro 3D reconstructed skin models under LAOS stress

This work discusses the first set of rheometric measurements carried out on commercially accessible juvenile and aged skin models under large amplitude oscillatory shear deformations. The results were compared with those of native male whole human and dermis-only foreskin specimens, catering to a few ages from 0.5 to 68 years, including specimens from a 23-year-old male abdomen. At large strains, strain thinning was more pronounced for the dermis of the young skins and for their whole skin counterparts. An inverse qualitative tendency was observed for the adult skins and the skin models. This can be explained by the high dermal collagen compactness associated with an incomplete epidermal proliferation. The qualitative Lissajous plots as well as the quantitative dimensionless indices analyzed using the MITlaos software indicated predominant nonlinear intracycle elastic strain stiffening and viscous shear thinning for all the native specimens at the maximum deformation. For the full thickness models, we have evidence of structure collapse and yielding under similar conditions. The whole skin specimen from the 68-year-old male showed smaller age-dependent nonlinear elastic contributions than the dermis, which we relate to the epidermal degeneration taking place during aging. Regardless of the age group, the models manifested more pronounced intercycle and intracycle elastic nonlinearities, and their magnitudes were significantly larger. The nonlinear elastic trends will serve as advanced standards for understanding and delineating the mechanical limits of destructive and non-destructive deformations of such unique biomaterials.

Insight into the weak strain overshoot of carbon black filled natural rubber

Weak strain overshoot (WSO) of loss modulus accompanying with strain softening under large amplitude oscillatory shear deformation is a common phenomenon that occurs in many systems but is still far from being clarified. Study about WSO has a strong practical significance, for it is directly related to sharp increase of energy dissipation of elastomer nanocomposites experiencing dynamic deformation of large strain amplitudes. Herein a systematical investigation was performed on WSO of uncured natural rubber (NR) and its low-loading carbon black compounds and a frequency-temperature-volume fraction diagram for the onset of WSO is firstly proposed to shed light on the mechanisms. A comparison of rheology behaviors of uncured polyisoprene rubber and NR and cured polyisoprene rubber suggests that WSO in NR originates from the non-isoprene fraction. Fourier-transform infrared spectroscopy measurement suggests the dissociation of hydrogen bonding at high temperatures, which accelerates the stress relaxation.

Rheology of fumed silica nanoparticles/partially hydrolyzed polyacrylamide aqueous solutions under small and large amplitude oscillatory shear deformations

Partially hydrolyzed polyacrylamide (HPAM) is one of the most widely used polymers for enhanced oil recovery operations. However, high temperature and high salinity in oil reservoirs restrict its functionality and performance. To alleviate this, incorporating fumed silica nanoparticles (NPs) in HPAM solutions was found to be very effective in harsh oil reservoir conditions to improve the efficiency of polymer flooding. Studying the flow behavior of hybrid polymer and fumed silica NP solutions under real reservoir conditions can be very challenging and hard to achieve due to continuously converging and diverging flow through porous structures. In this regard, rheological analysis of such systems under well-controlled flow histories within the capability of rotational rheometers can be of great importance to fully understand the mechanical response of these hybrid solution systems. In this study, two types of fumed silica NPs with different surface chemistries and two types of HPAM polymers with different molecular weights were dispersed/dissolved in deionized water. Linear viscoelastic properties of the hybrid solution systems were studied based on their step-stress (creep) and small amplitude oscillatory shear responses. As deformation in porous media can be rapid and large, consideration of nonlinear viscoelastic properties can be very crucial. The stress decomposition method and Lissajous–Bowditch curves were used to describe the intercycle and intracycle shear-thickening and strain-stiffening ratios quantitatively and qualitatively. In brief, linear and nonlinear rheology conjugated with thermogravimetric analysis and cryo-scanning electron microscopy imaging enabled us to characterize viscoelastic properties of the hybrid systems and link our observations to microstructural features. Through polymer bridging, the slightly hydrophobic fumed silica NPs (AEROSIL R816) had a unique ability to form interconnected, predominately elastic network structures in contrast to large agglomerated structures formed by highly hydrophilic AEROSIL 300. This has led to observing very different rheological behaviors, regardless of the HPAM polymer molecular weight, below and above a critical fumed silica NPs concentration.

Two-scale model for the effect of physical aging in elastomers filled with hard nanoparticles

A two-scale model is developed, and solved numerically, to describe the mechanical behavior of elastomers filled with hard nanoparticles. Of particular interest is the slow recovery of the elastic modulus after large-amplitude oscillatory deformation. To account for this effect, the physical aging of the glassy bridges between the filler particles is captured with two thermal degrees of freedom for the matrix material, namely a kinetic and a configurational one. Formulating the two-scale model enriched with aging in a nonequilibrium thermodynamics context, first results in a constitutive relation for the Cauchy stress tensor. Second, the dynamics of physical aging is described, which eventually results in the slow recovery of the elastic modulus with waiting time. The proposed model is investigated numerically under large amplitude oscillatory shear deformation. Of particular interest in this respect is the coupling of the micro-scale dynamics with the physical aging on the macroscopic scale. This coupling is examined in detail, both in an approximate way using a Gaussian approximation, as well as numerically, under specific conditions. It turns out that the CONNFFESSIT approach (Laso and Öttinger 1993 [46]) can not be employed for the numerical solution of the model under arbitrary loading conditions because of the novel structure of the two-level coupling term. While a procedure for solving the model numerically for the case of strong applied deformation is presented in this paper, other solution methodologies need to be sought for the cases of weak and no applied deformation.

Nonlinearities and shear banding instability of polyacrylamide solutions under large amplitude oscillatory shear

The response of semidilute entangled and salt-free solutions of aqueous polyacrylamide under large amplitude oscillatory shear deformations was studied in this work. We systemically probed the effects of four polymer concentrations from 5 to 15 wt. % and two molecular weights (5–6 and 18 M) at De > 1. The mitlaos software package was utilized to analyze the nonlinear moduli, among other nonlinear parameters. We found that the polymer concentration is the dominant parameter controlling the progression into the nonlinear regime. The trends of elastic decomposition indicate an intensive strain-rate softening behavior under high strain amplitudes. At high strain rates and at higher concentrations, however, a gradual transition from shear thickening to shear thinning could be noticed for the viscous dissipation. In addition, the effect of the measuring geometry was also considered, since the rheometer was coupled with a particle image velocimetry (PIV) system in the second part of this study. The PIV results suggest that the flow field is significantly altered during the oscillatory cycle. Banded profiles were observed for both molecular weights studied.

Validation of constitutive modeling of shear banding, threadlike wormlike micellar fluids

In this work, we assess the capability of two thermodynamically consistent, microstructure-based models to predict the rheology and microstructure of a model wormlike micellar surfactant solution known to exhibit shear banding undergoing transient simple shear and large amplitude oscillatory shear deformations in a cylindrical Couette rheometer. The microstructure of the surfactant solution was simultaneously measured during the rheometric tests using small angle neutron scattering and this data is used along with the bulk rheometry to critically evaluate the models. The first model is a new, two-species model specifically developed for wormlike micelles, whereas the second model is the well-known Giesekus model with solvent and diffusion. The new model accounts for the microstructural dynamics including flow-induced micellar breakage and recombination, which is shown to be necessary to predict some of the measured rheology and microstructure. More species should be included to improve the quantitative co...

A constitutive model for developing blood clots with various compositions and their nonlinear viscoelastic behavior.

The mechanical properties determine to a large extent the functioning of a blood clot. These properties depend on the composition of the clot and have been related to many diseases. However, the various involved components and their complex interactions make it difficult at this stage to fully understand and predict properties as a function of the components. Therefore, in this study, a constitutive model is developed that describes the viscoelastic behavior of blood clots with various compositions. Hereto, clots are formed from whole blood, platelet-rich plasma and platelet-poor plasma to study the influence of red blood cells, platelets and fibrin, respectively. Rheological experiments are performed to probe the mechanical behavior of the clots during their formation. The nonlinear viscoelastic behavior of the mature clots is characterized using a large amplitude oscillatory shear deformation. The model is based on a generalized Maxwell model that accurately describes the results for the different rheological experiments by making the moduli and viscosities a function of time and the past and current deformation. Using the same model with different parameter values enables a description of clots with different compositions. A sensitivity analysis is applied to study the influence of parameter variations on the model output. The relative simplicity and flexibility make the model suitable for numerical simulations of blood clots and other materials showing similar behavior.Electronic supplementary materialThe online version of this article (doi:10.1007/s10237-015-0686-9) contains supplementary material, which is available to authorized users.

A constitutive model for the time-dependent, nonlinear stress response of fibrin networks

Blood clot formation is important to prevent blood loss in case of a vascular injury but disastrous when it occludes the vessel. As the mechanical properties of the clot are reported to be related to many diseases, it is important to have a good understanding of their characteristics. In this study, a constitutive model is presented that describes the nonlinear viscoelastic properties of the fibrin network, the main structural component of blood clots. The model is developed using results of experiments in which the fibrin network is subjected to a large amplitude oscillatory shear (LAOS) deformation. The results show three dominating nonlinear features: softening over multiple deformation cycles, strain stiffening and increasing viscous dissipation during a deformation cycle. These features are incorporated in a constitutive model based on the Kelvin–Voigt model. A network state parameter is introduced that takes into account the influence of the deformation history of the network. Furthermore, in the period following the LAOS deformation, the stiffness of the networks increases which is also incorporated in the model. The influence of cross-links created by factor XIII is investigated by comparing fibrin networks that have polymerized for 1 and 2 h. A sensitivity analysis provides insights into the influence of the eight fit parameters. The model developed is able to describe the rich, time-dependent, nonlinear behavior of the fibrin network. The model is relatively simple which makes it suitable for computational simulations of blood clot formation and is general enough to be used for other materials showing similar behavior.

Strain-Phase-Resolved Dynamic SAXS Studies of BCC-Spherical Domains in Block Copolymers under LAOS: Creation of Twinned BCC-Sphere and Their Dynamic Response

We applied a large-amplitude oscillatory shear deformation (LAOS) to polystyrene-block-polyisoprene-block-polystyrene which had nearly randomly oriented grains of body-center-cubic lattice of spherical microdomains (BCC-sphere) before applying LAOS. Mechanical and structural responses of the BCC-sphere were simultaneously measured as a function strain phase ϕ and number of oscillatory strain cycles N by means of shear stress measurements and strain-phase-resolved dynamic small-angle X-ray scattering (DSAXS). The DSAXS revealed the following pieces of evidence: (1) LAOS first leads the BCC-sphere to attain two sets of the specific orientations as defined by A- and A′-sphere and by B- and B′-sphere, where both A- and A′-sphere and B- and B′-sphere are in the mirror symmetry with respect to {112} lattice plane which is parallel to the shear plane (the OXZ-plane with the OX- and OZ-axis defined as the shear direction and vorticity or neutral axis, respectively) for A- and A′-sphere or to the OXY-plane with the OY-axis defined as the velocity gradient direction for B- and B′-sphere. The two sets commonly have their ⟨111⟩ axis along the OX-axis. (2) Moreover, in parallel to attaining the specific orientations, both A- and A′-sphere and B- and B′-sphere are directed to form twinned BCC-sphere with their {112} lattice planes as the twin plane. While the events (1) and (2) described above were found to occur in the early stage of strain cycles (N ≤ 4), in the late stage of strain cycles (N > 4) the twinned BCC-lattice itself was found to undergo the oscillatory shear deformation in response to the applied shear strain under the fixed orientation of the {112} lattice plane and the ⟨111⟩ axis as described above. Moreover, we found that the shear deformations of the A- and A′-sphere under those fixed orientations are strikingly unequal due to dominance of the entropy elasticity of coronar block chains over the energy elasticity associated with the strain imposed on the lattice spacings. We elucidated that stress variations with ϕ and N, including nonlinear response with stress hardening, are closely related to the structural responses with ϕ and N, respectively, as described above.

Large amplitude oscillatory shear properties of human skin

Skin is a complex multi-layered tissue, with highly non-linear viscoelastic and anisotropic properties. Thus far, a few studies have been performed to directly measure the mechanical properties of three distinguished individual skin layers; epidermis, dermis and hypodermis. These studies however, suffer from several disadvantages such as skin damage due to separation, and disruption of the complex multi-layered composition. In addition, most studies are limited to linear shear measurements, i.e. measurements with small linear deformations (also called small amplitude oscillatory shear experiments), whereas in daily life skin can experience high strains, due to for example shaving or walking. To get around these disadvantages and to measure the non-linear mechanical (shear) behavior, we used through-plane human skin to measure large amplitude oscillatory shear (LAOS) deformation up to a strain amplitude of 0.1. LAOS deformation was combined with real-time image recording and subsequent digital image correlation and strain field analysis to determine skin layer deformations. Results demonstrated that deformation at large strains became highly non-linear by showing intra-cycle strain stiffening and inter-cycle shear thinning. Digital image correlation revealed that dynamic shear moduli gradually decreased from 8kPa at the superficial epidermal layer down to a stiffness of 2kPa in the dermis. From the results we can conclude that, from a mechanical point of view, skin should be considered as a complex composite with gradually varying shear properties rather than a three layered tissue.

Analysis of blood flow through a viscoelastic artery using the Cosserat continuum with the large-amplitude oscillatory shear deformation model

In this investigation, semiempirical and numerical studies of blood flow in a viscoelastic artery were performed using the Cosserat continuum model. The large-amplitude oscillatory shear deformation model was used to quantify the nonlinear viscoelastic response of blood flow. The finite difference method was used to solve the governing equations, and the particle swarm optimization algorithm was utilized to identify the non-Newtonian coefficients ( k υ and γ υ ). The numerical results agreed well with previous experimental results.

Application of FT Rheology to Industrial Linear and Branched Polyethylene Blends

AbstractNumerous analytical techniques are used to quantify branching topologies in polyethylene. One of these methods, FT rheology, studies the higher harmonic contributions of the stress response to large amplitude oscillatory shear deformation. The sensitivity of FT rheology in the presence of sparse long‐chain branched chains blended with linear ones is addressed. FT rheology is sensitive even for small concentrations of a partly long‐chain branched component blended with a linear melt (1.5–5 wt.‐%). The non‐linear parameters present a strong dependence on the fraction of long‐chain branched species in a polydisperse melt, the miscibility of which is confirmed via rheological techniques.magnified image

Rheology of multi‐walled carbon nanotube/poly(butylene terephthalate) composites

AbstractMulti‐walled carbon nanotube/Poly(butylene terephthalate) nanocomposites (PCTs) were prepared by melt compounding. The microstructure of PCTs was investigated using transmission electron micrographs and Fourier transform infra‐red spectrometer. The linear and nonlinear as well as transient rheological properties of PCTs were characterized by the parallel plate rheometer. The results reveal that the surface modification can improve the dispersion state of nanotube in matrix. PCTs present a low percolation threshold of about 1–2 wt % in contrast to that of Poly‐(butylene terephthalate)/clay nanocomposites. The network structure is very sensitive to both the quiescent and large amplitude oscillatory shear deformation, and is also to the temperature, which makes the principle of time‐temperature superposition (TTS) be valid on PCTs only in a very restricted temperature range. The stress overshoots to the reverse flow are strongly dependent on both the rest time and shear rate but show a strain‐scaling response to the startup of steady shear, indicating that the broken network can reorganize even under quiescent condition. The nanotube may experience the long‐range, more or less order during annealing process. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2239–2251, 2007

Detection and quantification of industrial polyethylene branching topologies via Fourier-transform rheology, NMR and simulation using the Pom-pom model

The significance of sparse long-chain branching in polyolefines towards mechanical properties is well-known. Topology is a very important structural property of polyethylene, as is molecular weight distribution. The method of Fourier-transform rheology (FTR) and melt state nuclear magnetic resonance (NMR) is applied for the detection and quantification of branching topology (number of branches per molecule), for industrial polyethylenes of various molecular weight and molecular weight distributions. FT rheology consists of studying the development of higher harmonics contribution of the stress response to a large amplitude oscillatory shear deformation. In particular, when applying large-amplitude oscillatory shear (LAOS), one observes the development of mechanical higher harmonic contributions at 3ω 1, 5ω 1,..., in the shear stress response. We correlate the relative intensity, I 3/1, and phase Φ 3 of these harmonics with structural properties of industrial polyethylene, i.e. polymer topology and molecular weight distribution. Experiments are complemented by numerical simulations, using a multimode differential Pom-pom constitutive model (DCPP formulation), by fitting to the experimental linear and nonlinear viscoelastic behaviours. Simulation results in the nonlinear regime are correlated with molecular properties of the “pom-pom” macromolecular architecture. Qualitative agreement is found between predicted and experimental FT rheology results.