Large Amplitude Oscillatory Shear Behavior Research Articles

Advances in large amplitude oscillatory shear Rheology of food materials

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

Understanding the transient large amplitude oscillatory shear behavior of yield stress fluids

A full understanding of the sequence of processes exhibited by yield stress fluids under large amplitude oscillatory shearing is developed using multiple experimental and analytical approaches. A novel component rate Lissajous curve, where the rates at which strain is acquired unrecoverably and recoverably are plotted against each other, is introduced and its utility is demonstrated by application to the analytical responses of four simple viscoelastic models. Using the component rate space, yielding and unyielding are identified by changes in the way strain is acquired, from recoverably to unrecoverably and back again. The behaviors are investigated by comparing the experimental results with predictions from the elastic Bingham model that is constructed using the Oldroyd–Prager formalism and the recently proposed continuous model by Kamani, Donley, and Rogers in which yielding is enhanced by rapid acquisition of elastic strain. The physical interpretation gained from the transient large amplitude oscillatory shear (LAOS) data is compared to the results from the analytical sequence of physical processes framework and a novel time-resolved Pipkin space. The component rate figures, therefore, provide an independent test of the interpretations of the sequence of physical processes analysis that can also be applied to other LAOS analysis frameworks. Each of these methods, the component rates, the sequence of physical processes analysis, and the time-resolved Pipkin diagrams, unambigiously identifies the same material physics, showing that yield stress fluids go through a sequence of physical processes that includes elastic deformation, gradual yielding, plastic flow, and gradual unyielding.

Large amplitude oscillatory shear behavior of thermoresponsive hydrogels: Single versus double network

Double network (DN) hydrogels have been recognized as new tough materials for several industries due to their precise structural platforms and significant properties. However, a comprehensive understanding of microstructural changes of DN hydrogels under large deformations is required to extend their applications. In this work, we use the large amplitude oscillatory shear (LAOS) technique to study the nonlinear response of a thermoresponsive κ-carrageenan/polyacrylamide DN system and its nanocomposite containing graphene oxide (GO) in comparison to its single network components. The results show a combination of strain stiffening and shear thickening nonlinear responses. The elastic intracycle strain stiffening was mainly attributed to the shear-induced increase in the elasticity of network chains and non-Gaussian stretching of individual chains. In addition, the orientation of the κ-carrageenan double helix segments and their enhancing effect on molecular orientation could be proposed as another possible mechanism of strain stiffening. The viscous intracycle shear thickening is also interpreted by two mechanisms of shear-induced temporary structure formation and reformation of dissociated physical interactions. It is also found that the GO nanosheets could contribute to the viscoelastic response by increasing the molecular interactions and, thus, amplification of energy dissipation. Furthermore, temperature dependency of the DN hydrogel owing to the conformational changes of the κ-carrageenan network at sufficiently high temperatures is used to investigate the effect of temperature on nonlinear behaviors. Increasing the temperature is found to have a significant decreasing effect on viscous nonlinearity, while its effect on the elastic nonlinearity was strongly dependent on the strain amplitude. This study provides a better understanding of the correlation between the microstructure and viscoelastic properties for designing tough hydrogels.

Effects of Breaking Methods on the Viscosity, Rheological Properties and Nutritional Value of Tomato Paste.

Ultrasound-assisted processing has potential application advantages as an emerging technology for preparing tomato paste. This work explored the influence of ultrasound break at 22 °C (US-Break-22) and 65 °C (US-Break-65) on the viscosity, rheological properties and nutritional values of newly prepared tomato paste, compared with traditional thermal break at 65 °C (Break-65) and 90 °C (Break-90). Results showed that the US-Break-65 paste had the largest apparent viscosity, yield stress, consistency coefficient, solid-like nature, and large amplitude oscillatory shear behavior, followed by the US-Break-22 paste, Break-90 paste, and Break-65 paste. Based on the results of the pectin-related enzymes, particle size, and serum pectin of the pastes, it was revealed that the above-mentioned properties were mainly determined by the particle size and pectin content in their serum. The level of ascorbic acid followed the order of US-Break-22 paste > US-Break-65 paste > Break-65 paste > Break-90 paste. The level of total carotenoids followed the order of US-Break-22 paste ≈ US-Break-65 paste > Break-90 paste ≈ Break-65 paste. The level of total cis-carotenoids followed the order of US-Break-65 paste > US-Break-22 paste > Break-90 paste > Break-65 paste. The level of phenolics and antioxidant activities followed the same order of US-Break-22 paste > US-Break-65 paste > Break-90 paste > Break-65 paste. Overall, the viscosity, rheological properties and nutritional values of the tomato pastes prepared by US-Break-65 and US-Break-22 were significantly higher than those prepared by Break-65 and Break-90. Therefore, ultrasound assisted processing can prepare high quality tomato paste and can be widely implemented in the tomato paste processing industry.

Effect of high-pressure homogenization on rheological properties of citrus fiber

The effect of high-pressure homogenization (0, 90, and 160 MPa) on the nonlinear rheological of citrus fiber with different concentrations was studied via large amplitude oscillatory shear tests. The strain-stress data obtained from the tests were processed by the Fourier transform rheology and Chebyshev stress decomposition methods to investigate the viscoelastic behavior of citrus fiber in the nonlinear region. The results showed that the citrus fiber suspension before homogenization presented Type I large amplitude oscillatory shear behavior, whereas the Type III shear behavior was found for fiber suspensions after high-pressure homogenization, showing enhanced intermolecular interaction. Lissajous-curves of fiber suspension showed that the viscosity in the nonlinear region increased when the concentration increase. Normalized 3rd elastic Chebyshev harmonics indicated that the 2.0 g/100 g fiber suspension at 1000% strain turned from strain-stiffening (0.00208) to strain-softening (−0.27498) through the homogenization. Furthermore, the high-pressure homogenization changed the shear behavior from shear-thinning to shear-thickening.

Small and large amplitude oscillatory shear behavior of supramolecular gels based on dopamine-boronic acid interactions

Blends of polymer solutions of poly(N-isopropylacrylamide-co-dopamine methacrylamide) (NIDO) and poly(N-isopropylacrylamide-co-4-vinylphenylboronic acid) (NIBA) in aqueous solutions were studied rheologically at pH ≈ 9. The functional catechol group of NIDO and the boronic acid group of NIBA could form coordinative complexes, which are strong, yet could be broken by high deformation, while they could reconfigure quickly within 1 min on a macroscopic scale. The linear and nonlinear behaviors of these materials vary significantly for different component mixing ratios. At a total polymer concentration of 10 w/v %, the 1:1 mixture (wNIBA/wNIDO) of the two polymers yields the strongest gel compared with asymmetric blends. The nonlinearity intensities (In/I1) of the materials increase proportionately with strain γ0, but once a significant nonlinearity is reached, they show lower nonlinearity intensities, which is unlike regular nonassociative single phase polymer melts and solutions. Interaction of polymer NIDO and NIBA and the formed supramolecular gels' properties will be clarified by large amplitude oscillatory shear characterization.Blends of polymer solutions of poly(N-isopropylacrylamide-co-dopamine methacrylamide) (NIDO) and poly(N-isopropylacrylamide-co-4-vinylphenylboronic acid) (NIBA) in aqueous solutions were studied rheologically at pH ≈ 9. The functional catechol group of NIDO and the boronic acid group of NIBA could form coordinative complexes, which are strong, yet could be broken by high deformation, while they could reconfigure quickly within 1 min on a macroscopic scale. The linear and nonlinear behaviors of these materials vary significantly for different component mixing ratios. At a total polymer concentration of 10 w/v %, the 1:1 mixture (wNIBA/wNIDO) of the two polymers yields the strongest gel compared with asymmetric blends. The nonlinearity intensities (In/I1) of the materials increase proportionately with strain γ0, but once a significant nonlinearity is reached, they show lower nonlinearity intensities, which is unlike regular nonassociative single phase polymer melts and solutions. Interaction of polymer NIDO...

Concentrated emulsions as novel fat replacers in reduced-fat and low-fat Cheddar cheeses. Part 2. Large amplitude oscillatory shear behavior

Lower-fat cheeses with desirable texture can be difficult to produce. The objective of this study was to characterize the effects of concentrated emulsions as a fat replacer on the viscoelastic properties of reduced-fat (15% fat) and low-fat (6% fat) Cheddar cheeses. Concentrated emulsions were prepared by adding a fish gelatin–gum arabic mixture at pH 5.0 and 3.6 to olive oil at a water:oil ratio of 30:70 (w/w). Cheddar cheeses containing emulsions were made by adding the emulsions to skim milk after adding starter culture and before renneting and subsequent cheesemaking. Two control cheeses at each fat level were produced using either olive oil or cream. Cheeses containing emulsions showed greater nonlinearity under large amplitude oscillatory shear, and smaller critical stress and moduli values compared with controls at all storage timepoints. These results were ascribed to greater casein network discontinuity and more open spaces created by aggregated emulsion droplets.

Large amplitude oscillatory shear behavior and gelation procedure of high and low acyl gellan gum in aqueous solution

The rheological properties of gellan fluid gels were investigated using large amplitude oscillatory shear (LAOS) technique in both linear and non-linear viscoelastic regimes, with consideration of high acyl (HA)/low acyl (LA) gellan ratio and Ca2+ concentration. The Lissajous curves and Chebyshev coefficients were used to analyze the LAOS data and successfully provided visual and quantitative representation of microstructural differences between HA and LA gellan gum, respectively. Temperature sweep measurements were performed to monitor the gelation procedure of gellan gum solution. The results show that HA gellan gum forms softer but more stable gels than LA gellan gum, especially at high temperature. And a synergistic interaction between HA and LA gellan gum may exist in the presence of abundant Ca2+ ions. The abovementioned study can allow a better understanding of structural characteristic of gellan gum and provide a practical approach to rheological assessment that facilitates the processing and diversified application of mixed gellan gum.

Large amplitude oscillatory shear behavior of graphene derivative/polydimethylsiloxane nanocomposites

Rheological properties of three different nanocomposites, consisting of graphene oxide (GO), reduced graphene oxide (rGO), and polyhedral oligomeric silsesquioxane grafted reduced graphene oxide (rGO-POSS) as nanofillers and polydimethylsiloxane (PDMS), were investigated by large amplitude oscillatory shear (LAOS). The viscoelastic nonlinearity of the three nanofluids groups was studied by Lissajous curves, local nonlinear viscoelastic moduli of an oscillatory shear cycle, and Fourier transform rheology as a function of filler concentration and increasing and decreasing strain magnitude. The nonlinear behavior of the nanofluids was compared to understand the variation of internal microstructures. Firstly, GO/PDMS composites behave with higher moduli and smaller linear viscoelastic range comparing to that of other two composites. Secondly, the elastic stress Lissajous curves of these composites changed from elliptic to rectangular with round the corner with increasing the filler level and strain amplitude. Thirdly, all these three nanofluids exhibited intra-cycle strain stiffening with increasing strains and shear thickening at intermediate strain and then shearing thinning with increasing strain further. Fourthly, higher harmonic intensity of rGO/PDMS increased with increasing strain and came to a plateau, while that of other two nanofluids reached a maximum and then decreased. It suggested that different surface functionalization of nanoparticles will present different rheological behavior due to formed different network and LAOS could be used as a potential helpful method to characterize rheological properties of nanocomposites, especially at higher shear strain.

Effect of fish gelatin and gum arabic interactions on concentrated emulsion large amplitude oscillatory shear behavior and tribological properties

Concentrated emulsions stabilized by proteins, polysaccharides, or a combination are the basis for many food products such as mayonnaise and heavy cream. However, fundamental influences of protein–polysaccharide interactions on concentrated emulsion tribological properties and large deformation behavior are often poorly understood, leading to difficulties in targeted development of concentrated food emulsions with palatable textures and good stability. Thus, the objective of this study was to characterize the effects of fish gelatin (FG)–gum arabic (GA) complexation on the large amplitude oscillatory shear (LAOS) and tribological behaviors of concentrated emulsions. Concentrated emulsions (oil phase volume fraction = 0.7) were prepared using FG–GA mixtures at different aqueous phase pH (3.6, 5.0, and 9.0) and characterized by rheometry and tribometry. Samples prepared with FG–GA mixtures at higher pH showed lower critical strains, increased extent of nonlinear behavior under LAOS (higher G′3/G′1 and G″3/G″1 values), increased strain hardening and shear thinning under LAOS (G′L/G′M and η′L/η′M values further from unity, respectively), and higher friction coefficients. These results were attributed to reduced FG–GA electrostatic complexation as pH increased from 3.6 to 9.0. Complexes formed at lower pH induced higher droplet monodispersity, greater network extension, and smaller oil droplets, resulting in greater structural stability to deformation. These stability differences would likely contribute to differences in food textures and stability under food processing and storage conditions.

Large amplitude oscillatory shear behavior and tribological properties of gum extracted from Alyssum homolocarpum seed

Fundamental understanding of polysaccharide lubrication and large-strain rheological behaviors is needed for targeted design of foods with more desirable texture and sensory attributes. Thus, the objective of this study was to investigate large amplitude oscillatory shear (LAOS) behavior and tribological properties of Alyssum homolocarpum seed gum aqueous dispersions at different concentrations (1-3% w/v) and temperatures (5-50 °C). Dispersions prepared at higher concentrations showed greater stability to permanent deformation under LAOS and lower friction coefficients. These results were attributed to greater molecular connectivity and structure development at higher concentrations. Increased temperature did not have strong effects on the tribological behavior of the dispersions; however, less permanent deformation at large strain was observed at higher temperatures. These results provide a more complete picture of Alyssum homolocarpum rheological behavior, which can be used to design foods with more desirable textures.

Strain Hardening and Strain Softening of Reversibly Cross-Linked Supramolecular Polymer Networks

The large amplitude oscillatory shear behavior of metallo-supramolecular polymer networks formed by adding bis-Pd(II) cross-linkers to poly(4-vinylpyridine) (PVP) in dimethyl sulfoxide (DMSO) solution is reported. The influence of scanning frequency, dissociation rate of cross-linkers, concentration of cross-linkers, and concentration of PVP solution on the large amplitude oscillatory shear behavior is explored. In semidilute unentangled PVP solutions, above a critical scanning frequency, strain hardening of both storage moduli and loss moduli is observed. In the semidilute entangled regime of PVP solution, however, strain softening is observed for samples with faster cross-linkers (k(d) ∼ 1450 s(-1)), whereas strain hardening is observed for samples with slower cross-linkers (k(d) ∼ 17 s(-1)). The mechanism of strain hardening is attributed primarily to a strain-induced increase in the number of elastically active chains, with possible contributions from non-Gaussian stretching of polymer chains at strains approaching network fracture. The divergent strain softening of samples with faster cross-linkers in semidilute entangled PVP solutions, relative to the strain hardening of samples with slower cross-linkers, is consistent with observed shear thinning/shear thickening behavior reported previously and is attributed to the fact that the average time that a cross-linker remains detached is too short to permit the local relaxation of polymer chain segments that is necessary for a net conversion of elastically inactive to elastically active cross-linkers. These and other observations paint a picture in which strain softening and shear thinning arise from the same set of molecular mechanisms, conceptually uniting the two nonlinear responses for this system.

Large amplitude oscillatory shear behavior of entangled polymer solutions: Particle tracking velocimetric investigation

Large amplitude oscillatory shear (LAOS) has been employed widely to probe the nonlinear behavior of complex fluids. Typically, the system undergoing LAOS has been assumed to experience homogeneous shear in each cycle so that material functions can be introduced to analyze the nonlinear dependence of these functions on the amplitude and frequency. Using particle-tracking velocimetric technique, we have carried a more systematic investigation on four different entangled polybutadiene (PBD) solutions with the number of entanglements per chain Z=13, 27, 64 and 119, extending well beyond the initial observations of shear banding in entangled PBD solutions under LAOS [Tapadia et al., Phys. Rev. Lett. 96, 196001–4 (2006a)]. At strain amplitudes γo>100% and frequencies higher than the overall chain relaxation rate, we observed, for the three samples with 27 or more entanglements per chain, the development of a thin “liquid” layer where severe chain disentanglement may have taken place. The thin liquid layer take...

Linear and nonlinear viscoelastic behavior of very concentrated plate-like kaolin suspensions

The viscoelastic behavior of very concentrated and electrostatically stabilized suspensions of kaolinite particles has been investigated in the linear and nonlinear regime as a function of volume fraction, ionic strength and in the presence of polymer at various concentrations. Material properties such as linear viscoelastic moduli and cohesive energy density are extensively enhanced by either increasing volume fraction or decreasing ionic strength. Attention has been paid to the large amplitude oscillatory shear behavior of concentrated suspensions of plate-like particles, characterized by a hump in G″ curves. Rheological investigation shows the extreme sensitivity of the intensity of the strain hardening in G″ to excluded volume, electrostatic and steric interactions. A physical interpretation of this nonlinear behavior has been proposed.

Large amplitude oscillatory shear behavior of PEO-PPO-PEO triblock copolymer solutions

Rheological properties of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer solution in both linear and nonlinear regions have been investigated. PEO-PPO-PEO triblock copolymer solution shows a dramatic change in mechanical properties as temperature changes. PEO-PPO-PEO triblock copolymer undergoes a transition from sol to gel with increase of temperature. During this transition the copolymer solution passes through three different stages, namely sol, soft gel, and hard gel. In our previous research (Hyun et al. in J Non-Newtonian Fluid Mech 55:51–65, 2002), large amplitude oscillatory shear (LAOS) behavior was found to be very sensitive to the generated microstructures. In this study, we investigated the relationship between the LAOS type and the microdomain structure. Newtonian behavior is observed in sol region, while there appear two kinds of LAOS types in the soft gel region. One is type I (G′, G′′ decreasing) and the other is a combination of type I and type IV (G′, G′′ increasing followed by decreasing). Type III (G′ decreasing, G′′ increasing followed by decreasing) is observed in the hard gel region. We compared the shape of stress curves, Lissajous pattern, and Fourier transform (FT) rheology of hard gel and soft gel under LAOS, and tried to relate the complex LAOS behavior with the microstructural change. From these investigations, it was found that the LAOS behavior and the stress pattern at large strain are closely related to the microdomain structure of PEO-PPO-PEO triblock copolymer, and provide a lot of useful information on the microstructures induced by large deformation.

Large amplitude oscillatory shear behavior of complex fluids investigated by a network model: a guideline for classification

Large amplitude oscillatory shear (LAOS) behavior of complex fluids, which form microstructures depending on their deformation history, has been investigated by using a network model. According to recent experimental observations, the LAOS behavior of complex fluids could be classified by at least four types: type I, strain thinning ( G′, G″ decreasing); type II, strain hardening ( G′, G″ increasing); type III, weak strain overshoot ( G′ decreasing, G″ increasing followed by decreasing); type IV, strong strain overshoot ( G′, G″ increasing followed by decreasing). To understand such complex behavior, we have applied a general network model. As there is little information available on the form of creation and loss rates of network junctions, we have modeled the creation and loss rates as exponential functions of shear stress. By adjusting the model parameters that define the creation and loss rates, the types of LAOS behavior observed in the experiments could be reproduced. Despite highly simplistic modeling, the model reproduced the types of LAOS behavior observed in the experiments, which means that the behavior can be explained in terms of the model parameters, that is, the creation and loss rates of network junctions. It is also suggested that the LAOS behavior can be effectively used as a tool for classifying complex fluids.

The Role of Temperature in the Entanglement Kinetics of a Polymer Melt

Large-amplitude oscillatory shear (LAOS) experiments were conducted at different temperatures on a molten low-density polyethylene standard, designated IUPAC LDPE X. Jeyaseelan et al. (1993) have successfully employed a simplification of transient network theory to describe the LAOS behavior of this polymer melt, at 150°C. The transient network is described by two kinetic rate constants, one for the formation of entanglements due to Brownian motion (k1), and another for the destruction of entanglements (k2) due to the imposed deformation. Upon comparison of the predictions of this transient network theory with the measured LAOS behavior of this polymer, we find that the kinetic rate constants k1 and k2 are invariant in the range of temperatures examined (150 to 190°C). The temperature dependence of departures from linear viscoelasticity is fully accounted for in the equilibrium entanglement kinetics.

A constitutive theory for polyolefins in large amplitude oscillatory shear

AbstractA versatile transient network theory has been used as a framework for the interpretation of large amplitude oscillatory behavior of polyolefin melts in terms of their entanglement kinetics. The model reasonably describes all previously published measurements of the large amplitude oscillatory shear behavior on melts. Seven polyolefins are examined, three new materials and four previously studied. A qualitative difference in the nonlinear behavior in large amplitude oscillatory shear has been identified between the polyethylenes examined and the two other polyolefins, polystyrene and polyisobutylene.

Relating blow moldability to large amplitude oscillatory shear behavior

AbstractThe large amplitude oscillatory shear test has been used to discriminate subtle differences in nonlinear viscoelasticity between two high density polyethyene blow molding resins with different processability. Structural network theory was used to explain the subtle differences in terms of entanglement kinetics with remarkable accuracy. The resin with better shape retention characteristics in programmed parison blow molding was found to have a higher kinetic rate constant for molecular re‐entanglement.

Structural network models for molten plastics evaluated in large amplitude oscillatory shear

The kinetic rate equation proposed by Mewis and Denn (1983) for their structural network model is found to predict accurately the large amplitude oscillatory shear behavior of molten low density polyethylene IUPAC X. Spectral analysis is used to compare the predictions of several kinetic rate equations. Frequency versus strain amplitude maps are constructed to examine each harmonic of the shear stress response predicted by the Mewis–Denn model. A Pipkin diagram is calculated for this model using contours for the amplitude of the third harmonic.