Dynamic Oscillatory Shear Tests Research Articles

Tribological properties of real foods using extended Stribeck curves and their relationship with nutritional and rheological parameters.

The tribological properties of 19 commercial food products, grouped into six categories (yogurt, dressings, spreads, porridges, emulsified sauces, and syrups) were investigated in relation to their rheological (dynamic oscillatory shear test) and nutritional properties (fat, carbohydrate, and protein). A tribological system (a glass ball and three polydimethylsiloxane pins) generated the extended Stribeck curve, monitoring friction factors (f) over an extended range of sliding speed (v) (10-8 to 100 m/s). Tribological parameters (f, v) at four inflection points dividing the frictional regimes (X1, breakaway point between the static and kinetic regimes; X1-X2, boundary; X2-X3, mixed; X3-X4, hydrodynamic regimes) and the slope between X3 and X4 (s) were subjected to principal component analysis and hierarchical clustering on principal components, using rheological and nutritional parameters as quantitative supplementary variables. Tribological patterns were predominantly influenced by viscosity, viscoelasticity, yield stress, fat content, and the presence of particles (e.g., sugar, proteins, and fibers) and pasting materials (e.g., starches and modified starches). The 19 tribological patterns were classified into 3 clusters: low f and s for fat- and/or viscoelastic-dominant foods (Cluster 1), low f and high s for food emulsions and/or those with low extent of shear-thinning (Cluster 2), and high f at the boundary regime either for the most viscous foods or for those in the presence of particulates (Cluster 3). These results suggest that the compositional and rheological properties have a more profound impact on the classification of complex tribological patterns than the categories of food products.

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.

Distinguishing between Linear and Star Polystyrenes with Unentangled Arms by Dynamic Oscillatory Shear Tests.

Linear and nonlinear viscoelastic properties of star polystyrene (PS) melts with unentangled arms were measured by using small-amplitude and medium-amplitude oscillatory shear (SAOS and MAOS) tests. For comparison purposes, such tests were also conducted on entangled linear and star PS melts. Interestingly, the linear viscoelastic properties of unentangled star PS were quantitatively described using the Lihktman-McLeish model for entangled linear chains, indicating that unentangled stars were indistinguishable from linear chains by using relaxation spectra. By contrast, the relative intrinsic nonlinearity (Q0), one of the MAOS material functions, exhibited a difference between unentangled star and linear PS. When the maximum Q0 value (Q0,max) was plotted against the entanglement number of span molecules (Zs), unentangled star PS exhibited larger Q0,max values than linear PS, which was quantitatively predicted via the multimode K-BKZ model. Therefore, in the unentangled regime, star PS was concluded to be characterized by intrinsically higher relative nonlinearity than linear PS.

Identification of gluten-like proteins in selected pod bearing leguminous tree seeds.

The protein composition, molecular weight distribution, and rheological properties of honey locust, mesquite, Kentucky coffee tree, and carob seed germs were compared against wheat gluten. Polymeric and Osborne fractionation protocols were used to assess biochemical properties. Dynamic oscillatory shear tests were performed to evaluate protein functionality. All samples had similar ratios of protein fractions as well as high molecular weight disulfide linked proteins except for the Kentucky coffee tree germ proteins, which were found to have lower molecular weight proteins with little disulfide polymerization. Samples were rich in acidic and polar amino acids (glutamic acid and arginine,). Rheological analyses showed that vital wheat gluten had the most stable network, while Kentucky coffee seed proteins had the weakest. High molecular weight disulfide linked glutenous proteins are a common, but not universal feature of pod bearing leguminous trees.

Density and Mechanical Properties of Selective Silicon Materials to Produce 3D Printed Paediatric Brain Model

This study presents a step towards exploring the possibility of using silicon materials as a surrogate to produce a multi-material 3D printed soft silicone brain model to be used in the investigation of Traumatic Brain Injury (TBI) in paediatric populations. Silicone represents a popular choice of material due to its viscoelastic properties, 3D printability, and capability to be tuned to possess different properties. Dynamic oscillatory shear tests were carried out for seven types of silicon materials at three different speeds against a different range of frequencies. The mechanical parameters response has been ranked on, which is the most appropriate to try. It also agrees with the range of reported paediatric brain tissue imitating grey and white matter as a surrogate brain material. Utilising of silicone for 3D printing represents a new approach to fabricate surrogate models that closely mimic biofidelic features and advance the medical engineering discipline.

Fabrication and mechanical behaviors of iron–nickel foam reinforced magnetorheological elastomer

Magnetorheological elastomers (MREs) have excellent magnetic-control mechanical properties, which ensures its great engineering application value in the field of vibration control. In this paper, the iron–nickel foam (INF) reinforced MREs with excellent magnetorheological (MR) properties were developed. The soft magnetic properties and three-dimensional (3D) foam structure of INF ensure an effective enhancement on the magnetic-control mechanical properties of MRE. The static and dynamic mechanical properties of the MRE were tested based on a parallel plate rheometer. Among them, static compression tests were carried out to study the static mechanical properties of MREs. The test results showed that INF reinforced MREs have excellent magneto-induced compression modulus. The effects of magnetic field, shear strain, and frequency on the dynamic mechanical properties of MREs have studied by the dynamic oscillatory shear tests. The test results revealed that the MRE has excellent MR properties under small strain. In addition, several successive tests were conducted to evaluate the response behavior under transient magnetic field and hysteresis properties of MREs under periodic magnetic field, and no obvious hysteresis in the repeated test curves have been observed. The INF reinforced MRE studied in this paper has potential application prospects in the field of micro-vibration control.

Viscoelastic properties of a novel hydrogel/foam composites for nucleus pulposus replacement

Neck and back pathologies cause considerable pain and suffering, and treatment costs tens of billions per year. A common source of problems is degeneration and herniation of the gel-like nucleus pulposus (NP) component of the intervertebral disc, and NP repair/replacement has been a long-term health care goal. We have investigated a novel class of hydrogel/foam composites to identify biocompatible materials with similar viscoelastic characteristics to the native tissue. Low acyl gellan gum (G) and agarose (A) in varying weight percentages were infused into Sugi® cellulose sponge material (F) to produce three candidate materials in addition to those samples without foam. Dynamic oscillatory shear tests and dynamic oscillatory axial compression test tests were conducted on the materials at frequencies between (f = 0.1–10 Hz) to measure elastic (storage) and viscous (loss) moduli in shear and compression conditions. The results show that hydrogel/foam composites show greater viscoelastic properties than hydrogel alone. Various materials of hydrogel and hydrogel/foam composite closely match the viscoelastic properties of native NP tissue.

Rheology⁻Microstructure Relationships in Melt-Processed Polylactide/Poly(vinylidene Fluoride) Blends.

In this study, small amplitude oscillatory shear tests are applied to investigate the rheological responses of polylactide/poly(vinylidene fluoride) (PLA/PVDF) blends and to correlate their viscoelastic properties with the morphological evolutions during processing. Although the analysis of the elastic moduli reveals some changes as a function of blend composition and processing time, the weighted relaxation spectra are shown to be more useful in detecting changes. The analysis demonstrates that when PVDF, i.e., the more viscous phase, is the matrix, the blend relaxes cooperatively and only a single relaxation peak is observed. By contrast, blends with highly concentrated morphologies do not fully relax, showing instead an upward increasing trend at longer times. This outcome is attributed to the broad distribution of highly concentrated droplets with a high probability of droplet–droplet contacts. Dynamic mechanical analysis (DMA) reveals that crystalline segmental motions attributed to the α-relaxation of PVDF at around 100 °C are restricted by the highly concentrated morphology of the 50/50 PLA/PVDF blend processed for 10 min. Relaxation analyses of the blends via dynamic oscillatory shear tests and DMA are shown to be powerful tools for investigating small microstructural changes in immiscible polymer blends.

Effect of vibration on adaptation of dental composites in simulated tooth cavities

This research investigated the effects of vibration on the rheological properties of dental composites and the adaptation of tooth cavity-composite interfaces. A portable vibratory packing device and two composites, micro-hybrid dental composite (MC) and nano-hybrid dental composite (NC), were evaluated. The frequency and amplitude of the vibratory packing device were measured. Dynamic oscillatory shear tests were conducted with varying frequency to examine the rheological properties of the composites. Twenty identical composite teeth with a Class I cavity were prepared and filled with one of the two composites. The composite was placed into a cavity using the vibratory packing device operating in either ON or OFF mode. After light-curing of the composite, the gap between the tooth and the composite was evaluated using micro-computed tomography. Two-way ANOVA was used to evaluate the effects of vibration and composite type on tooth-composite adaptation. The frequency of the vibratory packing device was 66.8 Hz. The complex viscosity, η*, of NC was higher than that of MC, and η* of both composites significantly decreased with increasing oscillation frequency. However, the application of vibration did not enhance adaptation at the tooth-composite interface.

Rheological Analysis of Live and Dead Microalgae Suspensions

We investigate the rheological properties of microalgae suspensions that are currently being used in various applications. Two kinds of microalgae, chlorella and Synechococcus, were used for preparation of the suspensions, and their rheological characteristics were analyzed experimentally. In order to evaluate the viability of algae, we performed live and dead tests using trypan blue staining assays. Morphological analyses for the algae were conducted using a scanning electron microscope (SEM) and an optical microscope (OP). We examined the viscoelastic behavior of the live and the dead algae suspensions by performing dynamic oscillatory shear tests.

Physicochemical and rheological properties of gelling pectin from Sosnowskyi's hogweed (Heracleum sosnowskyi) obtained using different pretreatment conditions

Using extraction with 0.7% aqueous ammonium oxalate, Sosnowskyi's hogweed pectins (yield 5–10%) with high molecular weight (200–700 kDa) and galacturonic acid content (70–85%), low degree of methylation (17–28%) and neutral sugar content (7–15%) were isolated from fresh, previously air-dried and frozen plant materials. All plant raw materials were pretreated with aqueous formaldehyde at 25 °C and dilute hydrochloric acid (pH 1.0 or 4.0, 50 °C). The different pretreatments of plant raw material slightly affected yield, chemical composition and molecular weight (average value and distribution) of hogweed pectin. The 13C-NMR spectroscopy indicated the similar structure of the pectins isolated from fresh and air-dried hogweed raw materials. The pectins were differed slightly in thermal degradation depending on the type of hogweed raw material. The aqueous solutions of hogweed pectins had a pseudoplastic flow behavior. Dynamic oscillatory shear tests showed that the pectin hydrogels in the presence Ca2+ (R∼0.6) represent true gels. The pectins from fresh plant material (pH 4.0) formed stronger gel networks (G' ∼2400 Pa) then compared to pectins from air-dried (G' ∼1400 Pa) and frozen (G' ∼900 Pa) plant raw materials. The pectin gelispheres of different size, particle shape, density and textural parameters were prepared by ionotropic gelation. The gelispheres derived from hogweed pectins (fresh and air-dried raw materials) were more stiffness compared to the gelispheres from the commercial low methoxyl apple pectin.

Viscoelastic properties of uncured resin composites: Dynamic oscillatory shear test and fractional derivative model

ObjectiveIn this study we analyze viscoelastic properties of three flowable (Wave, Wave MV, Wave HV) and one universal hybrid resin (Ice) composites, prior to setting. We developed a mathematical model containing fractional derivatives in order to describe their properties. MethodsIsothermal experimental study was conducted on a rheometer with parallel plates. In dynamic oscillatory shear test, storage and loss modulus, as well as the complex viscosity where determined. We assumed four different fractional viscoelastic models, each belonging to one particular class, derivable from distributed-order fractional constitutive equation. The restrictions following from the Second law of thermodynamics are imposed on each model. The optimal parameters corresponding to each model are obtained by minimizing the error function that takes into account storage and loss modulus, thus obtaining the best fit to the experimental data. ResultsIn the frequency range considered, we obtained that for Wave HV and Wave MV there exist a critical frequency for which loss and storage modulus curves intersect, defining a boundary between two different types of behavior: one in which storage modulus is larger than loss modulus and the other in which the situation is opposite. Loss and storage modulus curves for Ice and Wave do not show this type of behavior, having either elastic, or viscous effects dominating in entire frequency range considered. SignificanceThe developed models may be used to predict behavior of four tested composites in different flow conditions (different deformation speed), thus helping to estimate optimal handling characteristics for specific clinical applications.

Viscoelastic interactions between polydeoxyribonucleotide and ophthalmic excipients

This study investigated the interaction between polydeoxyribonucleotide (PDRN) and several ionic and nonionic isotonic agents, thickeners and a preservative that were employed as excipients in ophthalmic preparations. Interaction of each individual excipient and PDRN aqueous solution was evaluated by analyzing their rheological properties. Rheological properties of PDRN solutions were evaluated by dynamic oscillatory shear tests and values of elastic modulus (G′), viscous modulus (G″) and loss tangent (tan δ) were used to assess the relative changes in viscoelastic properties. At given concentrations, sodium chloride was found to show alteration in viscoelastic properties of PDRN solution while nonionic isotonic agents like d-glucose and d-sorbitol did not alter them. Similarly, nonionic water soluble polymers like polyvinylpyrrolidone (PVP) and hydroxypropyl methylcellulose (HPMC) also did not interact with PDRN to alter the viscoelastic properties. However, there were changes observed when carbopol 940 was used as a thickener. Therefore, PDRN was found to interact with ionic excipients and the interactions were negligible when nonionic materials were examined, which suggests that nonionic excipients are suitable to be formulated with PDRN.

Simulations of polydisperse magnetorheological fluids: A structural and kinetic investigation

A simulation method is proposed to explore the effect of particle size polydispersity in magnetorheology including Brownian motion. The method aims to extend the classical particle-level simulation methodology developed by Klingenberg et al. [J. Chem. Phys. 91, 7888–7895 (1989)] for the case of polydisperse magnetorheological (MR) fluids. The simulation study concerns the aggregation kinetics at rest as well as the rheological behavior under start-up of steady shear and dynamic oscillatory shear tests at increasing strain amplitudes. Results demonstrate that the effect of polydispersity is only relevant at the transition regime between magnetostatic to hydrodynamic control of the suspension structure. The yielding behavior is correlated to the structural characteristics (radial distribution functions, pair correlation functions, and angular connectivities) of the MR fluids before the onset of flow. A more abrupt transition is observed for polydisperse MR fluids because interparticle links are weaker in this case if compared to monodisperse suspensions in spite of the fact that polydisperse MR fluids exhibit a larger connectivity.

Characterization of Commercial Cheese Regarding Thermophysical Properties and Application of Multivariate Statistical Analysis to Elaborate Product Mapping

AbstractA variety of 25 commercial cheese were analyzed by means of four different methods to evaluate thermophysical parameters in order to estimate methods with high potential to differentiate between cheese varieties. Rheological properties of different temperatures were obtained by a dynamic oscillatory shear test. Furthermore, stretchability, meltability and the formation of free oil were obtained. Principal component analysis was applied to the data set to receive a mapping of the cheese. A reduction of the analyzed parameters to three principal components accounting for 76.3% of the total variation was achieved, indicating that the methods are well suited to characterize the cheese samples. Mapping of the obtained scores points out gaps and indicates missing products. This was demonstrated by including different experimental cheese with modified manufacturing protocols to the data set. Therefore, mapping supports cheese producers to design new products with specified characteristics by influencing the manufacturing protocol.Practical ApplicationsMapping of different commercial cheese visualizes cheese products in terms of thermophysical properties. This identifies missing products and supports accelerated product development by creating products with defined properties by influencing the manufacturing protocol. Furthermore, the availability of reliable methods and parameters to describe the thermophysical properties of cheese is of major importance for the cheese manufacturer in terms of quality management and characterizing cheese.

Studying the Interaction of Xanthan Gum and Pectin with Some Functional Carbohydrates on the Rheological Attributes of a Low-Fat Spread

Effects of xanthan gum (XG) (0.1 wt%) and pectin (PE) (0.5 wt%) alone and in combination with different concentrations (0.2 and 0.4 wt%) of locust bean gum (LBG), modified starch (MS), and Na-alginate (ALG) on some of the rheological characteristics of low-fat spreads, including flow behavior curves, rheological modeling, apparent viscosity, rheological modules (storage modulus (G′) and loss modulus (G″)), and delta degree (G″/G′) were studied. Results showed the power-law model was better than the Herschel–Bulkley model to describe the flow curve of dispersions. The k-value in the power-law model increased with increase in biopolymers concentration in solution. All samples exhibited shear-thinning flow behavior with a low yield stress. Dynamic oscillatory shear test showed that the spreads had a viscoelastic solid behavior with a gel-like structure. The G′ value was increased by increasing frequency from 0.03 to 15 Hz, while the G″ and G″/G′ values decreased. Also, MS in combination with XG and PE led to increase the G′ values of spreads in comparison with ALG and LBG. Moreover, microstructural and stability observations revealed that the spreads prepared with 0.1% XG-0.2% LBG significantly had the highest oiling out.

Influence of the prepolymer molecular weight and free isocyanate content on the rheology of polyurethane modified bitumens

Isocyanate-based modification is lately gaining acceptance as a successful way to give added value to bitumen, a crude oil refining by-product. In order to study the influence of prepolymer type on the rheological properties of the resulting binders, six prepolymers synthesized from polypropylene-glycols (PPG) with varying molecular weight (between 440 and 2425) and different molar excess of a polymeric MDI (4,4′-diphenylmethane diisocyanate) were used. Two modification procedures, either involving or not water addition were followed. The modification achieved depends on both the selected polyol molecular weight and the excess in MDI (i.e., free isocyanate content), although not in a similar extent. Viscous flow and dynamic oscillatory shear tests, at 60°C, demonstrated a much higher level of bitumen modification by using the prepolymer prepared with the polyol having a molecular weight of 940 and with a free isocyanate content of 17.4wt.%, mainly after addition of water. On the other hand, bitumen nature greatly affects the final rheological properties of these bituminous products. In that sense, modification results much more effective when conducted on bitumen with a well-developed colloidal microstructure.

Lyotropic Liquid Crystal Phases in Cellulose Acetate Phthalate/Hydroxypropyl Cellulose Blends

Cellulose and some of its derivatives form liquid crystalline solutions in a variety of solvents. The present work investigates cellulose acetate phthalate/hydroxypropyl cellulose blends in N,N-dimethylacetamide, in function of concentration and composition, by rheology, considering dynamic viscometry and oscillatory shear tests. The effects of composition, concentration, shear rate, and oscillatory deformation on the rheological functions determines the orientation or mobility of the chain segments in the shear field. Atomic force microscopy and polarized light microscopy studies on corresponding films show that specific interactions, such as the hydrogen bonds between cellulose acetate phthalate and the liquid crystalline component—hydroxypropyl cellulose, stabilizes the morphology, leading to the emergence of different formations typical for lyotropic liquid crystal phases. These studies contribute to a better knowledge of the specific interactions that generate and modify the liquid crystalline properties of cellulose derivatives, required by the applications in electronic domains.

Effect of chitosan molecular weight on the stability and rheological properties of β-carotene emulsions stabilized by soybean soluble polysaccharides

In this study, β-carotene emulsions were prepared using a two-stage homogenization process and adsorption of chitosan to anionic droplets coated with soybean soluble polysaccharides (SSPS). Effects of the molecular weights of chitosan on the stability and rheological properties of β-carotene emulsions were investigated. Results demonstrated that the ζ-potential, particle size and rheological properties of emulsions were greatly dependent on the chitosan molecular weight. It was found that the particle size of SSPS-stabilized emulsions increased with the rise of chitosan molecular weight at higher chitosan concentrations (>0.2 wt%). Chitosan molecular weight had a significant impact on the heat and light stability of β-carotene in emulsions. SSPS-stabilized emulsion with the adsorption of medium molecular weight-chitosan (MM-chitosan) was more stable than those with the adsorption of low and high molecular weight-chitosan (LM-chitosan and HM-chitosan). Dynamic oscillatory shear tests indicated that the viscoelasticity could be enhanced by the adsorption of higher molecular weight of chitosan onto the SSPS-coated droplet surfaces.

Bulk and interfacial viscoelasticity in concentrated emulsions: The role of the surfactant

The aim of this study was to investigate and compare bulk and interfacial viscoelasticity of emulsions stabilized with two surfactants of a markedly different nature: the ionic phospholipids mixture Epikuron 145V and the steric emulsifier Pluronic F68. Emulsions of olive oil in water were prepared by high-pressure homogenization using only one of these surfactants. The impact of the surfactant used on the final linear viscoelastic properties was investigated by means of small-amplitude dynamic oscillatory shear tests, obtaining the values of the storage and loss moduli as a function of frequency, as well as by retardation and relaxation essays. Our results show that for concentrated emulsions, the viscoelastic properties are considerably different depending on which surfactant is used, i.e., the employed surfactant influences to a major extent the bulk rheological properties. In order to explain these differences, an interfacial study of the adsorbed surfactant layers has been carried out, measuring interfacial tension and dilatational viscoelasticity by means of the pendant drop technique. A correlation between the results obtained in bulk and interface has been found.