Large Amplitude Oscillatory Shear Tests Research Articles

Effects of filler content on non-linear viscoelasticity of high fluorine content fluoroelastomer mixture investigated through large amplitude oscillatory shear tests

Effects of filler content on non-linear viscoelasticity of high fluorine content fluoroelastomer mixture investigated through large amplitude oscillatory shear tests

Rheology of plant protein–polysaccharide gel inks for 3D food printing: Modeling and structure–property relations

Plant protein–polysaccharide composite hydrogels and emulsion gels are attractive materials for production of edible inks for 3D food printing. Their ability to satisfy the printability requirements is conventionally evaluated in small- and large-amplitude oscillatory shear tests. A model is derived that describes experimental data in linear and nonlinear rheological tests on protein gels in a unified manner. The model is based on the population-balance approach and involves a reasonably small number of adjustable parameters. Fitting observations on soy protein isolate–xanthan gum, peanut protein–gellan gum, peanut protein–carrageenan, pea protein–carrageenan and pea protein isolate–flaxseed gum gels demonstrates that material parameters evolve consistently with composition of the gels. The governing equations describe adequately the effects of pH and ionic strength of aqueous solutions on the mechanical properties of the gels and predict the stress–strain Lissajous curves and the crossover amplitudes for transition from the solid-like to fluid-like response. Based on the analysis of observations in large-amplitude oscillatory tests with various frequencies, a mechanism is proposed for transition from the type-I (strain thinning) to type-III (weak strain overshoot) response of protein–polysaccharide gels.

Non‐linear viscoelasticity of carbon black–fluoroether rubber mixture studied by large amplitude oscillatory shear tests

AbstractNon‐linear viscoelastic characteristics of carbon black (CB)‐filled fluoroether rubber mixture samples are investigated by large amplitude oscillatory shear (LAOS) tests. Three analysis approaches based on LAOS tests are then used to discuss correlations between rheological behavior and CB‐filling amount. Each non‐linear viscoelastic parameter of the mixture presents a three‐stage characteristic with increasing CB content, which are attributed to the alteration of CB–elastomer network structure, corresponding to the state where gum continuous phase, CB–elastomer mesophase, and excessive CB agglomerates predominate in the mixture compound, respectively. According to the findings in engineering experiments, a CB content of 35–40 phr is recommended, taking into account tensile, hardness, and aging properties. Excessive CB agglomerates are found to reinforce CB–elastomer networks at elevated temperatures. For cold‐resistance properties, structural changes in CB–elastomer network are proven to exert little effect on Tg, but a higher CB content was found to slightly enhance the cold‐resistance coefficient, probably due to the decrease in velocity fraction of gum rubber.Highlights LAOS tests were utilized to study the influences of CB on fluoroelastomer; Three‐stage alteration was observed in the mixture with increasing CB content; Correlation between CB content and the engineering properties was discussed.

Effect of xanthan gum on physicochemical properties and 3D printability of emulsion-filled starch gels

The effects of xanthan gum (XG) concentration (0, 0.32%, 0.64%, 0.96%, 1.28%) on the rheological properties, microstructure, and 3D printing characteristics of emulsion-filled starch gels containing curcumin (XG-EFGs) were investigated. The results showed that the interaction between starch and XG led to an increase in mechanical strength with increasing XG concentration. The gels exhibited weak strain overshoot in large amplitude oscillatory shear tests, and the Lissajous curve shifted from elastic dominance to viscous dominance in the transition from linear to nonlinear behavior. The nonlinear parameters also demonstrated that the addition of XG led to strain stiffening and shear thinning behavior. Combining the rheological properties and 3D printing results, it was concluded that the addition of XG effectively improved the dimensional accuracy and stability of the printed products. Also, the addition of XG decreased the hardness, springiness, and gumminess of the XG-EFGs, changed the color brightness,and resulted in a superior delivery system for curcumin. This research contributes to the development of 3D printed gel foods fortified with lipophilic nutrients.

Rheology of cellulose nanocrystal and nanofibril suspensions

Nanocellulose is a sustainable nanomaterial and a versatile green platform that has attracted increasing attention. Although the wide applications of its aqueous suspensions are closely related to rheology, comprehensive studies of their rheological behavior, especially the yielding behavior, are still limited. Herein, to investigate the relationship between structure and rheological properties, the viscoelasticity, thixotropy and yielding behavior of two commonly used nanocelluloses, rod-shaped cellulose nanocrystals (CNCs) and filamentous cellulose nanofibrils (CNFs), were systematically investigated. The viscosity, viscoelasticity and thixotropic behavior of the suspensions were analyzed by steady-state shear, frequency sweep, creep-recovery, hysteresis loop, and three-interval thixotropic recovery tests. The yielding behaviors were evaluated through creep, steady-state shear, step shear rate, stress ramps, amplitude sweep, and large amplitude oscillatory shear tests. The rheological properties of the two typical suspensions showed a strong dependence on concentration and time. However, compared to CNC suspensions, CNF suspensions exhibited stronger thixotropy and higher yield stress due to the higher aspect ratio of CNF and the stronger structural skeleton of the suspensions as supported by Simha's equation and micromorphology analysis. This work provides a theoretical rheology basis for the practical applications of nanocellulose suspensions in various fields.

Study on dynamic properties of ultrasoft clay based on large amplitude oscillatory shear tests

In offshore engineering, the dynamic properties of ultrasoft clay in the seabed could affect the stability of offshore construction under dynamic loading. The typical rheological response of ultrasoft clay is studied based on the test results from large amplitude oscillatory shear tests with a rheometer. The ultrasoft clay undergoes three phases: the solid phase, transition phase and liquid phase, under dynamic loading. Modulus overshoot is observed when a phase transition occurs. The shear modulus and damping ratio of ultrasoft clay are studied based on the relationship between rheological parameters and dynamic parameters. The results show that the maximum shear modulus of ultrasoft clay could be expressed as a function of water content. Compared with general clay, the normalized shear modulus of ultrasoft clay decreases, and the damping ratio rapidly increases with increasing shear strain. Models describing the change in the normalized shear modulus and damping ratio with the shear strain of ultrasoft clay are suggested based on our test results. This study could aid in the evaluation of the stability of submarine structures at the seabed level under dynamic loading.

Identification of the effect of ionizing radiation on epichlorohydrin-based homo-, co-, and ter-polymers

In this study, the effects of ionizing radiation on a series of epichlorohydrin (ECH)-based polymers, namely poly(epichlorohydrin) (CO) homopolymer, poly(epichlorohydrin-co-ethylene oxide) (ECO) copolymer, and poly(epichlorohydrin-co-ethylene oxide-co-allyl glycidyl ether) (GECO) terpolymer, were examined. Polymers are irradiated at room temperature with accelerated electrons in the 0–150 kGy absorbed dose range. The effect of irradiation on the chain structure polymers was examined with sol-gel and rheological analyses. While ECH-based homo- and co-polymers showed crosslinking up to a specific dose, it was found that chain scission above a critical dose value was more dominant. On the other hand, in the ECH terpolymer, crosslinking tendency in the 0–80 kGy dose range was found to be dominant over chain scission. It was found that radiation stability varies depending on the initial molecular mass of the copolymer. Using the Charlesby–Pinner and Charlesby–Rosiak equations for each polymer, the chain scission and crosslink yield ratio (p0/q0), gelation dose (Dg), and virtual gelation dose (Dv) were determined and the effect of ionizing radiation on these polymers, which has increased in use in recent years, was examined. In this study, the effect of ionizing radiation on the long-chain branching value of ECH-based polymers was also examined using a rubber process analyzer (RPA) and large amplitude oscillatory shear testing (LAOS), and a mechanism for the exchange of branching has been proposed.

Nonlinear rheological performance characterization of styrene-butadiene-styrene and crumb rubber composite modified bitumen using large amplitude oscillatory shear tests

The crumb rubber (CR) recycled from waste tires can improve the mechanical properties of bitumen effectively. For the widely used modified bitumen today, it could work in nonlinear regime in many occasions. This study focuses on the nonlinear properties of styrene-butadiene-styrene (SBS) and CR composite modified bitumen (CMB) by analyzing the results of stress-controlled large amplitude oscillatory shear (LAOS) tests. The results show that the nonlinearity of SBS/CR CMB was significant under low load frequency, high temperature and high stress level. Lissajous curves at these conditions are distorted obviously due to the presence of higher-order harmonics. By analyzing the geometry parameters of Lissajous curves, it can be concluded that the incorporation of CR has a positive influence on the nonlinear properties of bitumen, which effectively improve the stress bearing capacity of bitumen. However, the high-order harmonic analysis indicates that improving the CR content simply does not always improve the performance of bitumen. Besides, the nonlinearity of SBS/CR CMB with lower CR content is similar to that of SBS modified bitumen through the value of I3/I1 and intrinsic nonlinear parameter Q, thus there are two critical CR contents for the prospect of modifying the nonlinearity of bitumen.

Structure-rheology relationship in monoolein liquid crystals

Hypotheses: Monoolein liquid crystals find use in foods and pharmaceuticals. Our hypotheses were: (a) liquid crystal symmetry dominates yielding and large deformation, and (b) strain rate frequency superposition (SRFS) may be used to determine mesophase long and short relaxation times.Experiments: Liquid crystal microstructure and rheology were characterised as a function of temperature and composition. Their structure was assessed using small angle X-ray scattering (SAXS) and polarised light microscopy. Small and large deformation rheology was characterised using frequency and amplitude sweeps, large amplitude oscillatory shear tests, and SRFS.Findings: We have contributed to the structure-rheology relationship governing the properties of the lamellar, cubic, and hexagonal mesophases. Initially, we characterised a number of monoolein-water binary phase transitions, which showed similar behaviour with earlier efforts. Frequency sweeps revealed that the cubic phases had the highest elasticity followed by the lamellar and hexagonal phases. The stiffening and thickening ratios, extracted from the Lissajous-Bowditch plots, were used to quantify intra-cycle non-linearities. The cubic phases displayed abrupt yielding with more pronounced stiffening and thinning behaviour compared to the others. Each liquid crystal phase displayed unique rheological behaviour upon large deformation and, by linking rheology with SAXS and composition, we show that their symmetry defined their rheology.

Large amplitude oscillatory shear (LAOS) behavior of chocolates of different compositions

The complex rheological response of chocolates of different compositions was analyzed in depth from stationary shear flow curves and large amplitude oscillatory shear tests. The samples have a wide range of cocoa content that controls the rheological behavior characterized by a yielding response. The strain amplitude at which the chocolates changed from elastic-dominated to viscous-dominated behavior ranged from 0.2 to 0.4%. In this region, the stress response to the applied sinusoidally oscillating shear strain showed transient overshoots whose values were similar to yield stress calculated using the Casson equation in continuous flow. The nonlinear response at the steady-state was analyzed. The Q0 nonlinearity parameter, obtained from Fourier Transform analysis, increases as the concentration of the solids conferring bimodality to the particle size distribution increases. In the study of intracycle nonlinearities, the analysis of the third-order Chebyshev elastic and viscous coefficients showed that the sample which contains the highest amount of solids different from cocoa exhibited the lowest strain-stiffening and the highest shear-thinning behaviors. Stress bifurcation analysis identified the beginning of the yielding transition and evidenced a nonlinear solid-like behavior before the solid-liquid transition. Analysis of Lissajous–Bowditch curves allowed the static and dynamic contributions of the yielding transition to be identified, and the full Sequence of Physical Process quantitative analysis captures the time-dependent nonlinear response of chocolates over the history of applied deformations.

Response of binder-filler systems into and beyond linear viscoelastic domain: Modeling and healing efficiency

This study is devoted to present insights into linear and nonlinear viscoelastic responses as well as the healing efficiency (HE) of binder-filler systems. To this aim, linear viscoelastic (LV) rheometric results were collected via implementing temperature and frequency sweep measurements, while for probing the nonlinear viscoelastic (NLV) response, large-amplitude oscillatory shear test was executed for various strain maxima. A parallel rheological framework assembled from 2 Yeoh models and hyperbolic-sine flow law, hereinafter abbreviated as 2Y-HS model, was explored to emulate the stress response for LV and NLV behavior of the binder-filler systems. In addition, a strain-dependent healing protocol was developed to test the HE of materials for varying strain-amplitudes. The tested binder-filler systems were blends of a plain binder and two mineral fillers, hydrated lime (HL) and silica fume (SF), added one at a time at different rates based on the best-practice limits. The binder-filler mastics undergone different behaviors into and beyond linear viscoelastic domain (LVD). The 2Y-HS model has efficiently constituted the rheometric results in a manner that elucidates the link between the stresses and strains for both LV and NLV behaviors. The proposed HE protocol showed its efficacy to evaluate the healability of materials at varying rest periods and stretch magnitudes. The damage-mending process at small-amplitude strains tended to improve better, and worst HE was attained as the strain level increases. The richer the asphalt binder with mineral filler, the less the HE is registered; however the binder-HL system is predisposed to heal much more than SF mastics.

Some open challenges in polymer physics*

AbstractThree subjects in polymer and soft matter physics are outlined in the present article. The first relates to concepts of an ideal glass transition. We describe work on ultra‐stable glass, either a 20‐million‐year‐old amber or a vapor deposited amorphous fluoropolymer, which examines the temperature dependence of the dynamics in a window between a low fictive temperature and the glass transition temperature. From this “finesse” of the problem of the geological time scales in sub‐glass temperature systems strong evidence that the divergence of the relaxation times at finite temperature from WLF‐types of extrapolation is not correct. The second topic is polymer nonlinear viscoelasticity as it relates to dynamic heterogeneity. We show results from mechanical hole burning experiments that suggest that dynamic heterogeneity arises from the nature of specific relaxation mechanisms rather than heterogeneous changes in, for example, the fictive temperature. Included is a discussion of large amplitude oscillatory shear testing and how it relates to characterization of nonlinear viscoelastic materials. The last topic addressed is the rheology of circular macromolecules. Here, we take a historical perspective and describe important new results from several laboratories that seem inconsistent. New works from our own studies on circular DNA are also discussed.

A Novel Method to Choose the Experimental Parameters in Large Amplitude Oscillatory Shear Rheology

Large Amplitude Oscillatory Shear (LAOS) rheology is a technique to analyze materials that are viscoelastic in nature. The raw values of stress and strain that were taken out from rheometer during the large amplitude oscillatory shear test are used in the constitutive models. The model parameters from the constitutive model are then analyzed on the materials being tested. Various test protocols and geometries will be used to analyze the materials of interest during LAOS rheological examination. The selection of test protocols and usage of geometry are less studied in testing various kinds of materials using LAOS. Cone and plate and parallel plate geometries are generally used for LAOS. The test protocols would be varying amplitude and varying frequencies. In the present work, quantification of relative performance of test protocols and geometry that have been used during the analysis of cross-linked poly vinyl alcohol hyaluronic acid (PVAHA) gels as material systems are studied using data envelopment analysis (DEA). The methodological approach using output oriented constant return to scale (CRS) and output oriented variable return to scale (VRS) are tested with the decision making units (DMU) as the geometry and test protocols used. These results are then combined with the Shannon's entropy to rank the efficient DMUs. Using Shannon's entropy combined with CRS and VRS, it is suggested that the use of parallel plate geometry with the test protocol of 0.5 rad/s and 50 frequency is best suitable for the cross-linked hyaluronic acid and poly vinyl alcohol gels examined.

Viscoelastic Rheological Behaviors of Polypropylene and LMPP Blends.

Dynamic oscillatory shear testing is used to investigate polymeric viscoelastic behaviors. Small and large amplitude oscillatory shear tests are the canonical method for characterizing the linear and nonlinear viscoelastic behaviors of any polymeric material. With prominent and abundant work on linear viscoelastic studies, the nonlinear behavior is evasive in terms of generating infinite higher harmonics in the nonlinear regime. For this reason, intrinsic nonlinearities from large amplitude oscillatory shear (LAOS) studies have recently been used for insights on microstructural behaviors. This study is carried out for linear and nonlinear viscoelastic behavior with a main focus on LAOS of isostatic polypropylene (iPP) and relatively new low molecular weight and low modulus polypropylene-based polyolefin (LMPP) blends. The morphological results showed reduced spherulitic crystal nucleus size and increased distribution in blends with increasing LMPP. The blends showed subtle linear viscoelastic responses with strong nonlinear mechanical responses to variant strain and stress compared to pure iPP. The intracycle strain thickening and intracycle strain stiffening of high-content LMPP blends were comparatively dominant at medium strain amplitudes.

Experimental investigation of the entanglement network and nonlinear viscoelastic behavior of a nano-SiO2 strengthened polymer gel

Polymer gels have been widely applied for conformance control and water shutoff in fractured and heterogeneous reservoirs. In this study, the rheological properties of a nanoparticle strengthened polymer gel were systematically studied, which was prepared by crosslinking between the hydrolyzed polyacrylamide (HPAM) and the water-soluble phenolic resin (WSPR). The primary objective of this work is to study the effects of nanoparticles on the properties of gelant and on the gelation performance. Specifically, the dispersion and degradation of polymers in the gelant were determined by dynamic light scattering (DLS) tests and rheological tests. The microstructures of gelant and polymer gel both in the presence and absence of nanoparticles were studied by Cryo scanning electron microscopy (Cryo-SEM). The results show that the nanoparticles in the gelant can effectively reduce the extent of polymer entanglement and aggregation, which would contribute to a more uniform network structure of the gel. Moreover, the nanoparticles in the gelant can increase the hydrophilicity of the polymer and inhibit the polymer degradation. The nanoparticles strengthened polymer gels also show a high strength and long-term thermal stability. The strength of gel with 0.4 wt% nanoparticles was four times higher than that of the gel without nanoparticles. The results of differential scanning calorimetry (DSC) tests also show that the addition of nanoparticles can increase the water holding capacity of the gel and efficiently restrain syneresis of the gel. Besides, the strain rate sensitivity and creep failure stress of gels were studied by large amplitude oscillatory shear tests and creep tests. The polymer gel with nanoparticles exhibits an extremely different nonlinear viscoelastic behavior, which also indicates that the structure of nanoparticle-strengthened gel has good ductility and toughness. Lastly, the nanoparticles strengthened gel has a high yield stress, which would contribute to a better blocking capacity in field applications.

Large Amplitude Oscillatory Shear testing for the performance grading of straight and polymer modified asphalt binders

This paper discusses the accuracy of performance grading through Large Amplitude Oscillatory Shear (LAOS) testing of asphalt binders, in comparison to results obtained by well-validated Double-Edge-Notched Tension (DENT) tests. The LAOS test is proposed as both a qualitative and quantitative method of analysing binder performance through Lissajous-Bowditch plots, and repeatable correlations between peak strain energy dissipation and CTOD values. The correlation between LAOS and Critical Crack Tip Opening Displacement (CTOD) in the DENT test is found to be strong. The findings of this preliminary study on a limited set of binders suggest that LAOS tests may provide practical measures of performance in high strain failure.

Nonlinear rheological characteristics of fine aggregate matrix based on FT-rheology

The fine aggregate matrix (FAM) is an important part of asphalt mixture, which has attracted much attention in recent years. The linear rheological properties of FAM have been well analyzed. However, asphalt pavements may also support loading in the nonlinear regime during its service. To comprehensively understand the rheological properties of FAM, their nonlinear rheological characteristics were tested by the large amplitude oscillatory shear test (LAOS) and analyzed by Fourier Transform (FT)-rheology. The nonlinear rheological characteristics of FAM were analyzed based on I3/I1,Q0 and Chebyshev coefficients. The effects of asphalt types, nominal maximum aggregate size (NMAS) and air voids on the nonlinearity of FAM were also investigated. The results reveal that the nonlinear rheological property of FAM is more significant than that of binders. I3/I1 of FAM firstly increases and then tends towards the plateau region with an increase in stress. And I3/I1 of FAM increases with decreasing frequency. The nonlinearity of unmodified FAM is obviously lower than that of modified FAM. The nonlinearity of FAM increases with increasing NMAS and decreasing air void. All studied FAM samples show stress softening and shear thinning behaviors under the studied test conditions.

Rheological properties and fractal-rheology analysis of peanut protein isolate suspension

This study focuses on the non-linear rheological property and microstructure of peanut protein isolate (PPI) aggregation suspension. The impact of higher harmonics (I3 and I5) on fundamental stress wave during large amplitude oscillatory shear test was studied. Rheological test show that storage modulus G′ and loss modulus G″ increased with increasing PPI concentration. The non-linear viscoelastic properties of PPI suspension with different concentration were investigated. Using confocal laser-scanning microscopy method, this research explored the microstructure of PPI suspension as well as the fractal dimensions. The new critical strain indirect method combined with Wu-Morbidelli model to calculate the fractal dimension (2.9225) is very close to the actual fractal dimension (2.9206). Fourier Transform Rheology was adopted to get the new critical strain for fractal dimension calculation, which was proved to be feasible. Keywords: peanut protein isolate suspension, rheological property, microstructure, fractal analysis DOI: 10.25165/j.ijabe.20201306.5717 Citation: Bi C H, Chi S Y, Hua Z, Li D, Huang Z G, Liu Y. Rheological properties and fractal-rheology analysis of peanut protein isolate suspension. Int J Agric & Biol Eng, 2020; 13(6): 220–226.

TEMPO-oxidized cellulose fibers from wheat straw: Effect of ultrasonic pretreatment and concentration on structure and rheological properties of suspensions

Cellulose and TEMPO-oxidized cellulose fibers (TOCF) from the wheat straw were prepared with ultrasonic and chemical treatments to investigate structure and functionalities. Sol-gel transition of TOCF suspensions has been investigated using rheology to unveil the roles of ultrasonic pretreatment and temperature at various concentration. It was found that TOCF extracted with or without ultrasonic pretreatment exhibit similar functional groups in FTIR. However, different crystal structures and thermal stabilities were revealed in XRD and TGA, respectively. The gelation was independent of the ultrasonic pretreatment, while the rheological properties were highly infuenced by the concentration and temperature of the TOCF suspensions. TOCF suspensions presented a strain thinning behavior in large amplitude oscillatory shear tests. Lissajous curves showed that the elastoplastic behavior was predominantly modulated by the fiber concentration and strain amplitude other than the ultrasonic pretreatment. These results could improve the understanding of the relationships between TOCF structure and rheological properties.

A small-scale study of nonlinear blood rheology shows rapid transient transitions

The mechanical properties of human blood are incompletely understood and constitute an underdeveloped area of study, prohibiting mechanically-based clinical diagnoses. Using the unique transient rheological signature of a blood sample, there is a possibility that blood rheology measurements could be used as a method of diagnosis and/or differentiation. We present here the response of blood to large amplitude oscillatory shear (LAOS) and reversing flow ramps, where hysteresis curves are typically formed. Results of these tests are visualized by blood “mechanical contours” that have the advantage of depicting the evolving mechanical properties of the material over a wide range of flow conditions. The sequence of physical process (SPP) method is applied to elucidate the changes undergone by the blood during the transient flows. This method is advantageous because it allows for the analysis of a wide range of transient flow protocols, rather than being restricted to strictly sinusoidal functions. We show a novel approach to the analysis of the large amplitude oscillatory shear tests in the form of mechanical contour maps. We also show the Cole-Cole plots and analysis for LAOS measurements using the same blood measurements. This allows a complete picture of the mechanical properties of the blood and a possible basis for comparison to pathological mechanical markers moving forward.