Small Amplitude Oscillatory Tests Research Articles

On the measurement of evolution of structural build-up of cement paste with time by static yield stress test vs. small amplitude oscillatory shear test

The structural build-up of cement-based materials is often characterized by the determination of the evolution of static yield stress with time. This property is crucial to many applications of concrete. However, the measurement of static yield stress may disturb the structure of cement-based material. As a consequence, the true structural build-up of the materials may not be detected. In this paper, the evolution of static yield stress and storage modulus (G′) determined by small amplitude oscillatory test was determined to characterize the evolution of the structural build-up of cement pastes. Results showed that G′ and static yield stress developed similarly with time. When the tests were carried out on the same sample, the measurement of static yield stress disturbed the structure of cement paste and had a significant effect on the following measurement of G′, but a slight effect on the following measurement of static yield stress.

Rheological and Microstructural Study of Wheat Doughs Partially Replaced with Mesquite Flour (Prosopis alba) and Added with Transglutaminase

The incorporation of different flours into wheat bread may pursue different objectives, such as increasing the nutritional quality of the products or the recovery of flour with little use in the industry. The “mesquite flour” (MF) is rich in sugar, fiber, and protein and is an interesting additive to wheat flour in baking. In this study, we used crude and thermally processed bread dough formulations of wheat flour (WF), replacing 15, 25, and 35% with mesquite flour. Furthermore, each formulation was tested for two levels (0.01 and 0.1%) of the enzyme transglutaminase (TG). Dough rheology was studied by small amplitude oscillatory compression tests, and the microstructure was analyzed by laser confocal microscopy using fluorescein isothiocyanate and rhodamine B as fluorophores. It was concluded that the incorporation of mesquite into the dough resulted in changes in the structure, as evidenced by the increase in tan δ, microscopic observations (loss of the filamentary and cross-linked gluten structure), and by the increase in the gelatinization temperature. The addition of TG led to dissimilar effects on doughs, depending on the formulation (wheat/mesquite content), but most encouraging results indicate the recovery of the structure, evidenced by a reduction in tan δ and the generation of a more filamentary structure in the dough with a higher content of mesquite flour. However, the effect of TG addition on “processed dough” was attenuated and the viscoelastic matrix of gluten did not recover.

Kaolinite suspension as a model fluid for fluid dynamics studies of fluid fine tailings

The rheology of fluid fine tailings is studied and compared with that of kaolinite suspensions having the same zeta potential, solid volume fraction and relatively similar particle size distribution. The suspensions were examined under shear and oscillatory deformation fields to investigate their yielding, aging, and steady-state flow behavior under shear rate and stress-controlled conditions. Using dynamic strain sweep experiments, it is shown that the samples exhibit a maximum in their loss modulus during yielding while they exhibit two different regimes of strain dependency in their fluidized regime. Samples are found to exhibit a plateau region in their stress-strain curves measured by the dynamic strain sweep experiments, due to the presence of flow instabilities. Small amplitude oscillatory tests are performed to study aging behavior of the suspensions with different shear histories. The aging process is found to depend strongly on the shear history of the samples prior to rest. Shear flow experiments under stress-controlled conditions show that both suspensions exhibit a plateau in their flow curves where a slight increase of the shear stress results in a dramatic change of the shear rate, implying the occurrence of shear-banding flow instability. This agrees with the behavior observed in the oscillatory deformation mode and implies that below a critical shear stress, no stable flow can be achieved in the suspensions. Fluid fine tailings and kaolinite suspensions are found to exhibit fairly similar rheological behavior, when their zeta potentials, solid volume fractions, and particle size distributions are matched.

Rheological properties of soft magnetic flake shaped iron particle based magnetorheological fluid in dynamic mode

In this work, the effect of particle shape (flakes) on the magnetorheological (MR) properties of an iron based MR fluid, constituted of two different volume fractions of particles dispersed in a liquid carrier, is studied. To compare the MR effect, spherical iron carbonyl particle based MR fluid is studied. In both MR fluids, linear viscoelastic behavior has been extensively investigated using small amplitude oscillatory analysis and magnetic sweep tests, in the presence and absence of a magnetic field (H). The amplitude sweep tests reveal that flake-based MR fluid shows a higher storage modulus compared to sphere-based MR fluid and saturates at a lower magnetic field strength. The variation of storage modulus with magnetic field strength shows an Hn dependence, where n varies from 2.2 to 2.4 for 20% volume fraction while it varies from 1.6 to 2 for a dilute sample. In the case of sphere-based MR fluid, at 20% volume fraction the variation of storage modulus is nearly linear with the magnetic field at low strain amplitude, and with increasing strain amplitude shows H2 dependence. At lower volume fraction in both cases, the loss modulus increases linearly with the magnetic field strength. The observed enhancement in the MR effect in the flake-based MR fluid is likely due to the stronger particle–particle interaction which results in higher friction between the particles. The sedimentation rate decreases by nearly 50% when flakes are used. The study reveals that one can use the irregular shaped particles for MR applications at low fields (∼80 kA m−1).

The Rheological Properties of κ-Carrageenan-Konjac Gum Mixed Gel

The rheological properties of κ-Carrageenan-Konjac Gum Mixed Gel were investigated by using dynamic rheological analysis. Results showed that the mixture of κ-Carrageenan and Konjac Gum had higher modulus of elasticity than single κ-Carrageenan or Konjac Gum. Blends solution has a good pseudo-plastic behavior at low concentrations, viscosity declined rapidly with shear rate increased. K+ and Ca2+ participated in the gelatin process and under the controlled condition might enhance force among molecules. With the temperature increasing G' and G" increased, and G' and G" presented suddenly change at 60-70 °C. Small amplitude oscillatory tests in the linear domain of viscoelasticity showed that κ-Carrageenan played the major role in the viscoelasticity of the mixture, and Konjac gum strengthened the gel-net configuration and stability.

Review on the Brownian Dynamics Simulation of Bead-Rod-Spring Models Encountered in Computational Rheology

Kinetic theory is a mathematical framework intended to relate directly the most relevant characteristics of the molecular structure to the rheological behavior of the bulk system. In other words, kinetic theory is a micro-to-macro approach for solving the flow of complex fluids that circumvents the use of closure relations and offers a better physical description of the phenomena involved in the flow processes. Cornerstone models in kinetic theory employ beads, rods and springs for mimicking the molecular structure of the complex fluid. The generalized bead-rod-spring chain includes the most basic models in kinetic theory: the freely jointed bead-spring chain and the freely-jointed bead-rod chain. Configuration of simple coarse-grained models can be represented by an equivalent Fokker-Planck (FP) diffusion equation, which describes the evolution of the configuration distribution function in the physical and configurational spaces. FP equation can be a complex mathematical object, given its multidimensionality, and solving it explicitly can become a difficult task. Even more, in some cases, obtaining an equivalent FP equation is not possible given the complexity of the coarse-grained molecular model. Brownian dynamics can be employed as an alternative extensive numerical method for approaching the configuration distribution function of a given kinetic-theory model that avoid obtaining and/or resolving explicitly an equivalent FP equation. The validity of this discrete approach is based on the mathematical equivalence between a continuous diffusion equation and a stochastic differential equation as demonstrated by Itô in the 1940s. This paper presents a review of the fundamental issues in the BD simulation of the linear viscoelastic behavior of bead-rod-spring coarse grained models in dilute solution. In the first part of this work, the BD numerical technique is introduced. An overview of the mathematical framework of the BD and a review of the scope of applications are presented. Subsequently, the links between the rheology of complex fluids, the kinetic theory and the BD technique are established at the light of the stochastic nature of the bead-rod-spring models. Finally, the pertinence of the present state-of-the-art review is explained in terms of the increasing interest for the stochastic micro-to-macro approaches for solving complex fluids problems. In the second part of this paper, a detailed description of the BD algorithm used for simulating a small-amplitude oscillatory deformation test is given. Dynamic properties are employed throughout this work to characterise the linear viscoelastic behavior of bead-rod-spring models in dilute solution. In the third and fourth part of this article, an extensive discussion about the main issues of a BD simulation in linear viscoelasticity of diluted suspensions is tackled at the light of the classical multi-bead-spring chain model and the multi-bead-rod chain model, respectively. Kinematic formulations, integration schemes and expressions to calculate the stress tensor are revised for several classical models: Rouse and Zimm theories in the case of multi-bead-spring chains, and Kramers chain and semi-flexible filaments in the case of multi-bead-rod chains. The implemented BD technique is, on the one hand, validated in front of the analytical or exact numerical solutions known of the equivalent FP equations for those classic kinetic theory models; and, on the other hand, is control-set thanks to the analysis of the main numerical issues involved in a BD simulation. Finally, the review paper is closed by some concluding remarks.

Effect of debranching on the rheological properties of Ca 2+–pectin gels

Water-soluble pectin (WSP) extract was subjected to controlled carrot pectin methylesterase treatment, thereby producing de-esterified pectin (DEP). Both WSP and DEP were incubated with a mixture of endo-arabinanase and α-L-arabinofuranosidase to yield partially debranched pectins (WSP DBr and DEP DBr respectively). Pectin samples were characterised in terms of degree of methylesterification (DM), neutral sugar content, and degree of branching (DBr). The characterised pectins were used for the preparation of pectin gels with high and low calcium ion (Ca 2+) concentrations. The rheological characteristics of the produced gels were evaluated by means of small-amplitude oscillatory tests. These characteristics include network development of the gel, gel strength (G′), gel elastic character and gel type. Partial debranching of pectin resulted in a reduction of the arabinose content (by approximately 50%) and caused a slight decrease in polymer DBr. Gels produced from semi-dilute solutions of partially debranched pectins showed network development profiles similar to those prepared from semi-dilute solutions of the corresponding non-debranched polymers. Yet, the former gels showed lower G′ values, poor gel elastic character and a “weaker” nature as compared to the latter. Next to Ca 2+ cross-links, the presence of long arabinose-containing side chains is suggested to play an important role in the rheological characteristics of Ca 2+–pectin gels.

Effect of de-methylesterification on network development and nature of Ca 2+-pectin gels: Towards understanding structure–function relations of pectin

Pectins of varying degree and pattern of methylesterification were produced through controlled de-esterification of highly esterified citrus pectin, using carrot pectin methylesterase (PME) (P-pectins), Aspergillus aculeatus PME (F-pectins) or sodium hydroxide saponification (C-pectins). Estimation of the degree of methylesterification (DM) and quantification of the pattern of methylester distribution in terms of absolute degree of blockiness (DB abs) enabled the characterisation of pectins. Characterised pectins were used for the preparation of Ca 2+-pectin gels with varying calcium ion (Ca 2+) concentration. The rheological characteristics of produced gels were evaluated by means of small-amplitude oscillatory tests. During gel formation, gel strength was monitored so as to allow assessment of network development. Based on the evaluation of mechanical spectra, the nature of the cured gels was established. Depending on Ca 2+ concentration as well as DM and DB abs, gels prepared from specific C-pectins (48 ≥ DM ≥ 26%; 9 ≤ DB abs ≤ 37%) and F-pectins (64 ≥ DM ≥ 29%; 9 ≤ DB abs ≤ 50%) showed a striking decrease of the gel strength with time, while gel networks produced from other pectins either displayed a continuous increase of the gel strength or verged towards pseudo-equilibrium within the observation time of 5 h. Furthermore, the DM, DB abs and Ca 2+ concentration influenced the evolution of Ca 2+-pectin networks from “structured liquids” to “strong gels”. Based on the experimental results, specific mechanisms of Ca 2+ interactions with pectins were (also) considered.

Rheological behavior and microstructure of 2,2′-dioxy- 1,1′-binaphthylphosphazene R/S random copolymer

Solutions of a binaphthoxy phosphazene copolymer (containing chiral 2,2′-dioxy-1,1′-binaphthyl units with 50% R and S configurations distributed along the chains) in N-methyl pyrrolidone were studied by means of continuous flow experiments and small amplitude oscillatory flow tests. A sudden viscosity decrease was observed in the polymer concentration range (39–40 wt %), evidencing a liquid-crystalline polymer behavior. This has been confirmed by other rheological methods which have demonstrated that, for a sufficiently high concentration, the solutions of the binaphthoxy phosphazene copolymer give rise to a lyotropic system with formation of rigid rods (axial ratio of 10) stacked parallel to each other. The lyotropic properties of our binaphthoxy phosphazene copolymer are compatible with a regular helical structure, similar to that found for a homoleptic binaphthoxy phosphazene, which contains only S configuration. This suggests that the chains of 50% R/S binaphthoxy phosphazene copolymer are, in average, close to the strictly alternating R-S copolymeric structure of the syndiotactic isomer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010

Nonlinear Viscoelastic Response of Thermoplastic-Elastomer Melts

Observations are reported on thermoplastic elastomer (ethylene-octene copolymer) melt in small-amplitude shear oscillatory tests and start-up shear tests with various strain rates in the interval of temperatures between 120 and 210 - C. Based on the concept of heterogeneous non-affine polymer networks, constitutive equations are developed for the thermo-mechanical behavior of a melt at three- dimensional deformations with finite strains. Adjustable parameters in the stress- strain relations are found by fitting the experimental data. The model is applied to the analysis of Poiseuille flow. The effects of temperature and pressure gradient on the steady velocity profile are studied numerically.

Gelation properties of salt-extracted pea protein induced by heat treatment

Gelation is one of the most important properties of plant proteins. In this paper, a low denaturation salt extraction method was used to extract pea (Pisum sativum L.) protein isolate from commercial pea flour. The gelation properties of this isolate were examined and compared to commercial products. The pea protein isolate followed the three-step process of gelation that is generally accepted for heat-induced gelation of globular proteins. The minimum gelation concentration of salt-extracted pea protein isolate (PPIs) was 5.5% while that of commercial pea protein isolate (PPIc) was 14.5%. The gelling point was in the range of 82–86 °C for 14.5% PPIs, 0.3 M NaCl at natural pH (5.65). With increasing heating rate, the gelling point tended to increase. Higher heating and cooling rates resulted in decreased final G′ (storage modulus) and G″ (loss modulus) values, indicative of decreased gel strength. A higher protein concentration resulted in higher G′ and G″ values and it was found that there was a power law relationship between protein concentration and G′ and G″. Tan delta (δ) values decreased with increasing protein concentration and at concentrations of 5.5% and above, tan δ remained constant which means the critical concentration for gel formation was 5.5%. The values of G′ and G″ for PPIs were greater than those of PPIc, and tan δ of PPIs was smaller, indicative of a stronger gel network. DSC data showed that PPIc had undergone denaturation whereas PPIs had not (ΔH = 15.81 J/g protein). Although rheometer data showed that the final G′ value of commercial soy protein isolate (SPIc) was smaller than that of PPIs, the gel prepared with SPIc was visually stronger than that of PPIs. The rheological data obtained with small amplitude oscillatory testing was not consistent with the actual observations. Overall, the low degree of denaturation of the PPIs resulted in a stronger gel than that of PPIc making the PPIs a more attractive food ingredient.

RHEOLOGICAL AND SEM STUDIES ON THE INTERACTION BETWEEN SPENT BREWER'S YEAST β‐GLUCANS AND κ‐CARRAGEENAN

ABSTRACT The microstructure of gel network produced byκ‐carrageenan (KC), and spent brewer's yeastβ‐glucans (BYG) and the two polymers' mixture were analyzed through rheological and scanning electron microscopy (SEM) experiments. Small amplitude oscillatory tests in the linear domain of viscoelasticity were applied to study the rheological properties of the two polymers in different mixing ratios. The mechanical spectra measurements gave neat evidence that although KC played the dominant role in forming the gel network, BYG contributed to the gel system, especially in the mixtures with low concentration (0.05 and 0.1 wt%) KC. BYG strengthened the gel network attributing to its entanglement with KC molecules, instead of inhibiting the KC to form ordered structure. It indicated that the two polymers were compatible with possible interactions that might be due to the intermolecular force and hydrogen bond between the two polymers. The microstructure's shape of the two polymers in SEM images demonstrated support explanation for the rheological properties.PRACTICAL APPLICATIONSThe fine particulate β‐glucans filled the cavity of the κ‐carrageenan network which enhances the mixed system gel strength. The results of this research might be useful for products development in food industry.

Rheological study of giant squid surimi ( Dosidicus gigas) made by two methods with different cryoprotectants added

Two new methods were designed for making surimi from giant squid ( Dosidicus gigas) muscle. The first is based on protein precipitation at the isoelectric point (type A), and the second on washing with an acid solution (type B). Chemical analyses (e.g. protein solubility, electrophoretic profile), structural analyses (scanning electronic microscopy) and above all rheological analyses were carried out. Small amplitude oscillatory tests were performed to evaluate the influence of these two methods on the viscoelasticity and gel-forming ability of squid surimi. The results showed that method B preserves the functionality of the myofibrillar proteins better, thus making for a better gel structure than method A. Moreover, the addition of different cryoprotectants (sorbitol + sucrose, sorbitol + trehalose, trehalose alone), resulted in essential differences between the two kinds of surimi. In surimi A, trehalose favoured less initial protein aggregation and hence a thermorheologically stable structure, with a better gelation profile than sorbitol + sucrose or sorbitol + trehalose, in surimi, suwari-gels and definitive-gels alike. However, in B samples the influence of different cryoprotectants was not discernible.

Viscoelasticity of polyethylene/montmorillonite nanocomposite melts

Observations are reported on low-density polyethylene melts reinforced with montmorillonite nanoclay at concentrations of filler ranging from 0 to 10wt.% in small-amplitude shear oscillatory tests, start-up tests with a constant strain rate, and relaxation tests. Constitutive equations are derived for the time-dependent response of a nanocomposite melt at three-dimensional deformations with finite strains. The model accounts for (i) inhomogeneity in the distribution of nanoparticles, (ii) non-affinity of an equivalent polymer network with sliding junctions, and (iii) evolution of energies of inter-chain interaction driven by orientation of clay platelets. It is demonstrated that the stress–strain relations correctly describe the experimental data and adjustable parameters change consistently with nanoclay content.

Characterisation of alginate gels using quasi-static and dynamic methods

The rheological behaviour of the calcium salts of several commercial mannuronic and guluronic alginates in the time and frequency domain was assessed by quasi-static (uniaxial compression and compressive stress relaxation) and oscillatory dynamic tests. Both tests gave almost the same range (1–10%) of apparent linear viscoelasticity. Use of the Friedrich and Heymann model [Friedrich, Chr., & Heymann, L. (1988). Extension of a model for crosslinking polymer at the gel point. Journal of Rheology, 32, 235–241] allowed the transient responses of the network of alginate gels to be approximately characterised by a single relaxation function, its empirical parameters being independent of the experimental test provided that the applied strains were kept within the elastic and proportional limit. The linear interrelation between the material compressive ( S α ) and shear ( S β ) parameters was roughly checked using an independent estimate of the Poisson’s ratio via the NOL test [Warfield, R. W., Cuevas, J. E., & Barnet, F. R. (1970). Single specimen determination of Young’s and bulk moduli of polymers. Rheologica Acta, 9, 439–446] Since the information collected from simple compression or shear tests in the linear viscoelasticity regime was inter-convertible, the small amplitude oscillatory dynamic tests, which are simpler, quicker, less material consuming and thus less expensive than the quasi-static ones, might be recommended to discriminate between alginates of different origin and composition.

Calcium-mediated gelation of an olive pomace pectic extract

Pectic raw material was extracted from the alcohol insoluble residue of olive pomace. After purification, the olive pectic extract (OPE) contained 48% of galacturonic acid (GalA) and 31% of arabinose, in a total sugar content of 72%, and a degree of methylesterification (DM) of 43%. Phase diagrams were established to define the physical state of the OPE/calcium systems, at pH 3 and 7, as a function of GalA and calcium concentration. The rheological properties of the OPE/calcium systems were investigated by small-amplitude oscillatory tests. Kinetics of gel ageing and the viscoelastic properties of the cured gels were evaluated as a function of GalA and calcium concentration at pH 3 and 7. Compared with the observed behaviour of a citrus pectin, taken as representative of a commercial low-methoxyl pectin, the OPE showed higher critical GalA and calcium concentrations for gelation to occur, a larger region corresponding to homogeneous gel, and gels characterised by lower viscoelastic moduli, at similar GalA and calcium concentrations.

Viscoelasticidad lineal de estructuras líquido-cristalinas de un sistema tensioactivo no iónico nonilfenol etoxilado/agua

In this work the linear viscoelastic behaviour of micelar and liquid-crystalline phases in a polyoxy-ethylene glycol nonylphenyl ether (EO a =10)/water system was studied. A linear viscoelastic characterization using small amplitude oscillatory tests was carried out. The Maxwell and Generalized Maxwell models fit the linear viscoelastic functions of micellar and hexagonal phases respectively, fairly well. On the other hand, the lamellar phase shows a plateau region characteristic of highly structured systems. As may be deduced from the experimental results, dynamic measurements constitute an effective method to study the structural changes occurring in phase diagrams.

Thermal gelation of globulin from Phaseolus angularis (red bean)

The heat-induced gelation properties of red bean globulin (RBG) were studied under the influence of salts and several protein structure perturbants. The viscoelastic properties of the gels were evaluated by small amplitude oscillatory tests and creep experiments. Gel structure developed progressively when a protein dispersion (≈10% w/v) was heated from 25 to 95 °C, and both the storage modulus (G′) and loss modulus (G″) increased rapidly during cooling. The addition of NaCl at lower concentrations led to increases in G′ and G″ values, with decreased creep compliance, suggesting higher viscoelasticity. At higher salt concentrations, viscoelasticity was decreased, and the optimum NaCl concentration to produce maximum gel rigidity was 0.2 M. Sodium dodecyl sulfate and urea caused more pronounced reduction of the gel moduli than dithiothreitol and N-ethylmaleimide. The data suggest that hydrophobic interactions and hydrogen bonding play an important role in heat-induced gelation, while electrostatic interactions and a balance of attractive–repulsive forces are also important. The gels formed at 95 °C exhibited a homogenous microstructure with extensive cross-links and sheet-like network structures.

Frequency Effects on Dynamic Stability Derivatives Obtained from Small-Amplitude Oscillatory Testing

As a result of a continuing program of work to establish a basic understanding of the aerodynamic phenomena that ine uence agility, stability, and control of future combat aircraft cone gurations, it has become clear that the conventional stability or aerodynamic derivative model for the representation of aerodynamic loads in the aircraft equations of motion is no longer adequate. This paper discusses the limitations of the stability derivative model for modern combat aircraft maneuvers, in particular the problem of motion frequency effects in static and dynamic derivatives derived from small-amplitude oscillatory wind-tunnel tests, and presents an alternative modeling technique based on the concept of an aerodynamic transfer function. Nomenclature A = in-phase component of rolling moment response AR = amplitude ratio ai, bi, ci = constants in generalized transfer functions B = in-quadrature component of rolling moment response b = wingspan, m Cl = rolling moment coefe cient, L/qSb Clb,att = attached e ow component of steady-state derivative Clb,0

Starch and Amylopectin — Rheological Behavior of Gels

AbstractRheological behavior of starch and amylopectin gels was evaluated by small amplitude oscillatory testing using the storage modulus (G′), loss modulus (G″) and the complex viscosity (n*). It was found for the three starches (normal and waxy corns, and amaranth) that at low frequency the viscous component G″ had a major contribution on the gel structure than the elastic G′ and that the complex viscosity (n*) diminished when the frequency was increased. Amaranth amylopectin showed G″ values higher than those of G′. Corn commercial and waxy corn amylopectins presented a similar behavior in the G′ values. Normal corn amylopectin gave the highest complex viscosity values.