Small Amplitude Oscillatory Shear Research Articles

The effects of freeze-thaw cycles on the rheological properties of yeasted and non-yeasted frozen bread doughs

The effects of repeated freeze-thaw cycles on yeasted and non-yeasted frozen bread doughs were investigated by a series of fundamental rheological tests, including small stress amplitude oscillatory test, shear creep-recovery, and uniaxial and planar extensional tests. Results showed that yeasted and non-yeasted doughs tested under both shear and extension using small and large deformations were rheologically different. Yeasted dough exhibited significantly higher storage modulus (G’) as measured by the small stress amplitude oscillatory test and lower compliance measured in creep recovery tests. The effects of freeze-thaw cycles were clearly displayed in non-yeasted doughs, especially in large deformations rheological tests. Resistance to deformation of non-yeasted dough was altered by freeze-thaw cycles, indicated by creep recovery tests conducted under 500 Pa creep stress. The extension failure stress of non-yeasted dough was affected by freeze-thaw cycles, indicated by uniaxial and planar extensional tests. The negative impact of freeze-thaw cycles in yeasted doughs was more pronounced for dough examined with extensional tests. This was revealed by a decreased strain hardening behavior of doughs after freeze-thaw cycles when tested by uniaxial and planar extensional tests. Large deformation tests, particularly under extensional deformations can assist in the understanding of the freeze-thaw impact on dough matrices.

Viscoelastic behavior of oral mucosa. A rheological study using small-amplitude oscillatory shear tests

The purpose of this work was to determine the viscoelastic behavior of porcine and human oral mucosa under physiological conditions of temperature, hydration and chewing. The linear elastic and viscous shear moduli of these soft tissues were determined by small-amplitude oscillatory shear (SAOS) tests at masticatory frequency using a stress-controlled rheometer equipped with an immersion cell on punched biopsies 8 mm in diameter. Non physiological conditions of temperature were also used to access other parameters such as the denaturation temperature of collagen.First, the different parameters such as normal force, frequency and maximal strain were adjusted to obtain reliable data on porcine mucosa. The optimal normal force was 0.1N and the linear viscoelastic limit was found for a strain amplitude of 0.5% for both 0.1 and 1 Hz. The storage moduli of porcine mucosa, ranging from 5 to 16 kPa, were in the same range as cutaneous tissues determined by SAOS at equivalent frequencies. The storage modulus, superior to the loss modulus G″, indicates a predominant elastic contribution to shear stress in chewing conditions.Second, this protocol evidenced an influence of the anatomic site of the mouth on the viscoelastic behavior of porcine mucosa, mandibular biopsies having higher storage moduli than maxillary biopsies. Temperature scans showed the mechanical manifestation of collagen denaturation in the 60–70 °C range as previous calorimetric analyses. Finally, this mechanical protocol was successfully adapted to characterize human mucosa in an elderly population. It was shown that the elastic modulus is impacted by local inflammation (gingivitis), decreasing significantly from 6 ± 1.4 kPa to 2.5 ± 0.3 kPa.

High-temperature rheological behavior and non-isothermal pyrolysis mechanism of macerals separated from different coals

It is a challenge to accurately characterize the caking behavior of coal after thermal softening and its reaction mechanism. In this work, the formation behavior of metaplast during coal macerals coking was investigated using high-temperature confocal laser scanning microscopy and high-temperature small-amplitude oscillatory shear rheometer, the source of diversities in thermal fluidity of coal was revealed by thermogravimetric-mass spectrometry analysis and kinetic-thermodynamic theory calculations. The results showed that although vitrinite was the generator of metaplast in the thermoplastic stage, the expansion rate of vitrinite from coking coal is more than 70% greater than that from gas coal for two consecutive times. Moreover, the total weight loss of vitrinite from gas coal was about 1.262 times higher than that from coking coal, but the latter exhibited more generous aliphatic groups in pyrolysis products. In the thermal flow interval, the reaction activation energy of vitrinite and inertinite from coking coal and gas coal was 271.0 ± 0.7, 302.0 ± 1.5, 241.0 ± 0.1 and 300.25 ± 1.55 kJ/mol, respectively. Eventually, the kinetic and thermodynamic mechanism parameters of raw coal and macerals had favorable correspondence regularity, and macerals with the most prominent parameters would be dominant in the overall thermal properties of raw coal.

Small and large oscillatory shear behaviors of gelatin/starch system regulated by amylose/amylopectin ratio

This work explores the influence of starch amylose/amylopectin ratio on the gel-related features of gelatin/starch system using small and large amplitude oscillation shear methods. The higher self-aggregation and self-entanglement ability of amylose reduced the miscibility of gelatin and starch, and increases zero-shear viscosity (ŋ0) and reduces sol-gel transition temperature (Tgel) by enhancing the difficulty of molecule movement and thus the difficulty of gel formation. The gelatin/amylopectin-rich system has higher gel hardness and wider linear viscoelastic region, which are related to the higher integrity and uniformity of network structure. The gelatin/amylose-rich system shows enhanced ability to resist deformation against external shear forces (suggested by higher storage and complex modulus) under small amplitude oscillatory shear (SAOS), which is ascribed to the larger rigidity and entanglement degree of amylose. At strain amplitude up to 50% (middle amplitude oscillatory shear, MAOS), gelatin/amylose-rich system exhibits reduced structure recovery ability (reflected by larger semi-minor axis of ellipse, and lower strain amplitude for inflexion of elastic stress) under MAOS, but enhances restructuring capacity at strains of 500% and 1000% (large amplitude oscillatory shear, LAOS) (indicated by occurrence of secondary loop) than gelatin/amylopectin-rich system. Those seemingly contradictory phenomena are correlated with the preference of hydrogen bond forming ability among amylose rather than with gelatin. This weakens interactions between amylose and gelatin and thus inhibits recovery of bulk structure under MAOS, but is favor for the formation of amylose aggregations, which is helpful for the local structure restructuring and thus enhances structure restructuring capacity under LAOS. The results help us comprehensively understand the gel-related properties of gelatin/starch system and are valuable for rational design of gelatin/starch systems with improved gel-related features.

Effect of Cold Atmospheric Pressure Argon Plasma Jet Treatment on the Freeze-Dried Mucilage of Chia Seeds (Salvia hispanica L.).

In the present study, the effects of the treatment of chia seeds with a cold atmospheric pressure plasma jet (CP) using argon as a working gas for different times (30, 60, and 120 s) on the rheological, structural, and microstructural properties of the freeze-dried mucilages at -54 °C were investigated. All mucilage gels showed pseudoplastic flow behavior, and CP treatment of chia seeds increased the viscosity of mucilages, probably due to the cross-linking between polymer molecules. The dynamic rheological analysis revealed that all mucilages were elastic gels and that CP treatment improved the elastic properties in a treatment time-dependent manner. Large amplitude oscillatory shear (LAOS) results showed that freeze-dried mucilages showed Type I strain-thinning behavior. Similar to small amplitude oscillatory shear (SAOS) results, CP treatment has affected and improved the large deformation behavior of mucilages depending on treatment time. Meanwhile, Fourier transform infrared spectroscopy (FTIR) revealed the incorporation of hydroxyl groups onto the surface and the formation of C-O-C glycosidic bonds during plasma treatment. Scanning electron microscope (SEM) micrographs showed the formation of denser structures with CP treatment time. Regarding color properties, CP treatment decreased the lightness values of mucilages. Overall, this study showed that CP is an effective way to modify both the SAOS and LAOS properties of freeze-dried chia mucilage and improve viscosity.

Steady State and Dynamic Oscillatory Shear Properties of Carbon Black Filled Elastomers

A correlation between the steady shear viscosity and complex dynamic viscosity of carbon black (CB) filled rubbers was found by evaluating the Cox-Merz rule and an alternative approach originally proposed by Philippoff for dilute polymer solutions, but since applied to amorphous polymers and concentrated suspensions. This was done by measuring the rheological properties of 16 industrially important rubber mixes containing CB N660 at concentrations of 20 and 35% by volume. A capillary rheometer at various shear rates and a dynamic oscillatory shear rheometer at small and large amplitude oscillatory shear (SAOS and LAOS) were used. The apparent viscosity, storage and loss moduli, complex dynamic viscosity and Fourier transform harmonics were measured. Generally, the shear stress, storage and loss moduli increased with increasing CB loading. Also, the ratio of third and fifth stress harmonics to first harmonics increased with increasing strain amplitude and filler loading. Viscous Lissajous figures (shear stress versus shear rate) at a strain amplitude of 14% showed a nearly linear response for compounds containing CB at 20% by volume. All other shear stress responses demonstrated a strong nonlinearity. The stress waveforms at a strain amplitude of 140% for compounds containing 35% CB by volume displayed a backwards tilted shape expected for highly filled compounds. The stress waveforms at a strain amplitude of 1,000% tended toward a rectangular shape expected for pure polymer. Generally, the nonlinear response of the compounds appeared to be dominated by the filler at strain amplitudes of 14% and 140% and by the rubber matrix at a strain amplitude of 1,000%. The Cox-Merz rule was not applicable for any of the compounds with their complex dynamic viscosity being greater than the apparent viscosity. However, a modification of the approach proposed by Philippoff provided reasonable agreement between the apparent viscosity and complex dynamic viscosity.

Star-to-Bottlebrush Transition in Extensional and Shear Deformation of Unentangled Polymer Melts

A series of model poly((±)-lactide) (PLA) graft copolymers was synthesized by ring-opening metathesis polymerization and used to probe the star-to-bottlebrush transition in shear and extensional flows. Ten samples with backbone degrees of polymerization 11 ≤ Nbb ≤ 420 were investigated using small-amplitude oscillatory shear (SAOS) and extensional rheometry measurements. Each contained one PLA side chain of length Nsc = 72 per two backbone repeating units on average (graft density of z = 0.5). The star-like to bottlebrush transition was identified at Nbb = 50–69 using SAOS. In extension, melt strain hardening is absent in the star-like melts (Nbb ≤ 50) but is prominent in the bottlebrush limit (Nbb > 69). The onset of melt strain hardening occurs at a time scale equivalent to the Rouse time of the backbone. A molecular interpretation of these results builds upon recent conjectures related to strain-induced increases in interchain friction in bottlebrush polymers. These findings will be useful in designing bottlebrush melts that strain harden, which is critical in various types of processing methods involving extensional flows, including foaming, 3D printing, and film-blowing.

Effect of specific surface area on the rheological properties of graphene nanoplatelet/poly(ethylene oxide) composites

The rheological properties of poly(ethylene oxide) containing graphene nanoplatelets (GNPs) having different specific surface areas (SSAs) are studied using steady shear and small amplitude oscillatory shear experiments. A series of GNPs having SSAs ranging from 175 ± 5 to 430 ± 13 m2/g was prepared using a thermomechanical exfoliation process. The complex viscosity, moduli, and yield stress of the composites increase with SSA, whereas electrical and rheological percolation threshold concentrations decrease, suggesting that higher SSAs promote filler network formation. Modeling of small amplitude oscillatory shear data using a two-phase model confirms that hydrodynamic effects dominate at low concentrations below 8 wt. %, where the particles are noninteracting. At higher concentrations, the response is dominated by filler-phase contributions. We demonstrate that the two-phase model parameters can be used to track the exfoliation of graphite into GNPs. Fitting of rheological percolation curves using Utracki and Lyngaae–Jørgensen models at low concentrations (noninteracting regime) resulted in aspect ratios between 19 and 76. At high concentrations (interacting particles), the aspect ratios determined by the Krieger–Daugherty model ranged between 5 and 24 due to aggregation. The highest aspect ratios (defined as the ratio of major dimension to minor dimension) were associated with GNPs that had the highest SSA of 430 m2/g. Strain sweeps revealed that the critical strain for the onset of nonlinear viscoelasticity scaled with SSA above the percolation threshold. The scaling relationships of the critical strain and storage modulus with volume fraction were used to infer the fractal dimensions of filler networks.

Concentration Scaling on Linear Viscoelastic Properties of Cellular Suspensions and Effects of Equilibrium Phase Behavior.

Concentration scaling on linear viscoelastic properties of cellular suspensions has been studied by rheometric characterisation of Phormidium suspensions and human blood in a wide range of volume fraction under small amplitude oscillatory shear experiments. The rheometric characterisation results are analysed by the time-concentration superposition (TCS) principle and show a power law scaling of characteristic relaxation time, plateau modulus and the zero-shear viscosity over the concentration ranges studied. The results show that the concentration effect of Phormidium suspensions on their elasticity is much stronger than that of human blood due to its strong cellular interactions and a high aspect ratio. For human blood, no obvious phase transition could be observed over the range of hematocrits studied here and with respect to a high-frequency dynamic regime, only one concentration scaling exponent could be identified. For Phormidium suspensions with respect to a low-frequency dynamic regime, three concentration scaling exponents in the volume fraction Region I (0.36≤ϕ/ϕref≤0.46), Region II (0.59≤ϕ/ϕref≤2.89) and Region III (3.11≤ϕ/ϕref≤3.44) are identified. The image observation shows that the network formation of Phormidium suspensions occurs as the volume fraction is increased from Region I to Region II; the sol-gel transition takes place from Region II to Region III. In combination with analysis of other nanoscale suspensions and liquid crystalline polymer solutions reported in the literature, it is revealed that such a power law concentration scaling exponent depends on colloidal or molecular interactions mediated with solvent and is sensitive to the equilibrium phase behaviour of complex fluids. The TCS principle is an unambiguous tool to give a quantitative estimation.

Rheological Performance of High-Temperature-Resistant, Salt-Resistant Fracturing Fluid Gel Based on Organic-Zirconium-Crosslinked HPAM

Development of low-cost, high-temperature-resistant and salt-resistant fracturing fluids is a hot and difficult issue in reservoir fluids modification. In this study, an organic zirconium crosslinker that was synthesized and crosslinked with partially hydrolyzed polyacrylamide (HPAM) was employed as a cost-effective polymer thickener to synthesize a high-temperature-resistant and salt-resistant fracturing fluid. The rheological properties of HPAM in tap water solutions and 2 × 104 mg/L salt solutions were analyzed. The results demonstrated that addition of salt reduced viscosity and viscoelasticity of HPAM solutions. Molecular dynamics (MD) simulation results indicated that, due to electrostatic interaction, the carboxylate ions of HPAM formed an ionic bridge with metal cations, curling the conformation, decreasing the radius of rotation and thus decreasing viscosity. However, optimizing fracturing fluids formulation can mitigate the detrimental effects of salt on HPAM. The rheological characteristics of the HPAM fracturing fluid crosslinking process were analyzed and a crosslinking rheological kinetic equation was established under small-amplitude oscillatory shear (SAOS) test. The results of a large-amplitude oscillation shear (LAOS) test indicate that the heating effect on crosslinking is stronger than the shear effect on crosslinking. High-temperature-resistant and shear-resistant experiments demonstrated good performance of fracturing fluids of tap water and salt solution at 200 °C and 180 °C.

Gaborheometry: Applications of the discrete Gabor transform for time resolved oscillatory rheometry

Oscillatory rheometric techniques such as small amplitude oscillatory shear (SAOS) and, more recently, medium amplitude oscillatory shear and large amplitude oscillatory shear (LAOS) are widely used for rheological characterization of the viscoelastic properties of complex fluids. However, in a time-evolving or mutating material, the build-up or breakdown of microstructure is commonly both time- and shear-rate (or shear-stress) dependent, and thixotropic phenomena are observed in many complex fluids including drilling fluids, biopolymer gels, and many food products. Conventional applications of Fourier transforms for analyzing oscillatory data assume the signals are time-translation invariant, which constrains the mutation number of the material to be extremely small. This constraint makes it difficult to accurately study shear-induced microstructural changes in thixotropic and gelling materials, and it is becoming increasingly important to develop more advanced signal processing techniques capable of robustly extracting time-resolved frequency information from oscillatory data. In this work, we explore applications of the Gabor transform (a short-time Fourier transform combined with a Gaussian window), for providing optimal joint time-frequency resolution of a mutating material’s viscoelastic properties. First, we show using simple analytic models and measurements on a bentonite clay that the Gabor transform enables us to accurately measure rapid changes in both the storage and/or loss modulus with time as well as extract a characteristic thixotropic/aging time scale for the material. Second, using the Gabor transform we demonstrate the extraction of useful viscoelastic data from the initial transient response following the inception of oscillatory flow. Finally, we consider extension of the Gabor transform to nonlinear oscillatory deformations using an amplitude-modulated input strain signal, in order to track the evolution of the Fourier–Tschebyshev coefficients of thixotropic fluids at a specified deformation frequency. We refer to the resulting test protocol as Gaborheometry (Gabor-transformed oscillatory shear rheometry). This unconventional, but easily implemented, rheometric approach facilitates both SAOS and LAOS studies of time-evolving materials, reducing the number of required experiments and the data postprocessing time significantly.

Emulsion-based oleogelation using octenyl succinic anhydride modified granular cold-water swelling starch

Oleogels were produced starting from Pickering emulsions, stabilized by octenyl succinic anhydride (OSA) modified high amylose (HS-OSA), waxy (WS-OSA), and granular cold-water swelling starch (GCWS-OSA). GCWS-OSA had the highest degree of OSA substitution (DS) and contact angle with the oil-water interface, and the smallest emulsion droplet size (0.0149, 80.4°, 12.58 μm), followed by WS-OSA (0.0098, 76.2°, 22.83 μm) and HS-OSA (0.0049, 73.3°, 31.50 μm). In small amplitude oscillatory shear (SAOS), all template emulsions and oleogels had G’ > G’’ (tan δ ≤ 0.1) and behaved as soft viscoelastic solids. The highest G’ was observed for WS-OSA and GCWS-OSA, which clearly produced a much stiffer material. In large amplitude oscillatory shear (LAOS), WS-OSA and GCWS-OSA oleogels showed a progressive disruption of the microstructure, which resulted in an increase in viscous dissipation. At the highest strain of 20.5%, WS-OSA and GCWS-OSA were showing completely plastic behavior, whereas the structure of the HS-OSA based oleogel still displayed significant residual elasticity, indicating only partial disruption of the microstructure. WS-OSA and GCWS-OSA also had a much higher strain overshoot (Payne effect) in G”, then the sample based on HS-OSA. The higher DS and granular structure of GCWS-OSA contributed to a more stable Pickering emulsion and stiffer oleogel. • Pickering emulsions were used as a template to create oleogels. • Emulsions were stabilized using three types of OSA-modified rice starch particles. • Emulsions and oleogels were characterized using SAOS and LAOS measurements. • The Pickering emulsions produced oleogels with high stiffness. • The stiffness of oleogels can be tailored by choice of the appropriate starch.

Incorporating chitin nanocrystal yields stronger soy protein gel: Insights into linear and nonlinear rheological behaviors by oscillatory shear tests

Chitin nanocrystals (ChNs) were successfully fabricated from shrimp and their effects on the microstructure and gelling properties of glucono-δ-lactone-induced soy protein isolate (SPI) were investigated. Firstly, transmission electron microscopy (TEM) showed that the average length and width of ChNs were 208.8 nm and 19.2 nm, respectively. The zeta potentials of ChNs changed from +38.6 mV at pH 3.0 to +16.4 mV at pH 8.0. Subsequently, the gel strength, water holding capacity (WHC) and viscoelasticity of the composite gels were improved by increasing the ChNs concentration from 0 to 1.0% (w/v). Based on low field nuclear magnetic resonance (LF-NMR) analysis, the decrease in PT 22 and increase in PT 21 indicated that the improvement of WHC was associated with the transformation of free water into immobilized water. Scanning electron microscopy (SEM) showed that the incorporation of ChNs promoted the formation of a denser and more homogenous gel network. All composite gels showed high frequency dependence and a typical Type I (strain thinning) network behavior. The increase in both elastic and viscous moduli further showed the improvement in the microstructure of composite gels, which was induced by the addition of ChNs. The Sequence of Physical Processes (SPP) analysis provided a detailed deformation history of gel microstructure by the evolution of the instantaneous storage (G′t) and loss moduli (G″ t ). In this method, gel samples experienced various degrees of microstructural rearrangements at small amplitude oscillatory shear (SAOS) region (γ = 0.64%) and large amplitude oscillatory shear (LAOS) region (γ = 100%). • Formation of stronger SPI gels through incorporation of ChNs. • ChNs increased the gel strength, WHC and viscoelasticity of SPI gels. • ChNs provided a denser and more uniform microstructure for SPI gels. • All gels showed high frequency dependence and type I behavior. • The gel microstructure showed stepwise changes during large deformation.

Impact of Photoactive Monomer Location in Photoresponsive Block Copolymer/Ionic Liquid Solutions

By incorporating a photoactive moiety into a block polymer, the phase behavior can be controlled with light. Previous studies have looked at situating azobenzene, a common photoresponsive molecule, along the backbone of the polymer as a pendant group, and even as part of the solvent rather than as a comonomer. Here, we study the effect of the positioning of pendant azobenzene groups along the polymer backbone on the lower critical disorder–order transition of poly(methyl methacrylate)-block-poly(benzyl methacrylate) (PMMA-b-PBnMA, or MB) in the ionic liquid 1,3-dimethyl imidazolium bis(trifluoromethylsulfonyl)imide. Using small-angle X-ray scattering and ultraviolet (UV)-irradiated small-amplitude oscillatory shear rheology, the placement of azobenzene statistically along the benzyl methacrylate backbone (MBsA) is compared to locating it as a midblock between the PMMA and the PBnMA (MAB) or as an end block after the PBnMA (MBA). Two concentrations of polymer in the ionic solvent were studied, 35 and 50 wt %. At 35 wt %, MBsA microphase-separated at 60 °C, MBA at 100 °C, and followed by MAB at 120 °C, a trend that was repeated at 50 wt %. MBsA was the only polymer to order onto a lattice at 35 wt %, forming hexagonally close-packed spheres. Both MBsA and MBA formed hexagonally packed cylinders at 50 wt %. MBsA consistently ordered onto a lattice over the temperature range of interest, while MBA only did so at 50 wt %, and MAB remained disordered at both concentrations. MBsA was also the only sample of the three to successfully transition reversibly between order and disorder with light. Therefore, adjusting the location of the azobenzene units within the thermo- and photoresponsive polymer solution significantly changes the overall behavior of the solutions and the ability to control that behavior with light and temperature.

Multiscale modeling of complex fluids under SAOS and LAOS using a combined FENE transient network model

The multiscale modeling of complex fluids under small and large amplitude oscillatory shear flow using non-linear kinetic and transient network models is presented. The kinetics of microstates is analogous to chemical kinetics, which defines the physical macromolecule interaction in a Newtonian fluid, and the concentration of microstates defines a variable maximum length of extension for each microstate. The effect of important parameters like viscosity ratio, chain length, viscoelasticity, kinetic rate constants, for different initial entanglement scenarios (entangled, disentangled and aleatory) are analyzed. The Lissajous curves for the shear stress and the first normal stress difference versus the instantaneous strain or strain-rate are shown. The self-intersection of the Lissajous curves or secondary loops is shown to depend on the kinetic rate constants, the maximum extension length, and the elasticity.

On the rheology and magnetization of dilute magnetic emulsions under small amplitude oscillatory shear

A dilute magnetic emulsion under the combined action of a uniform external magnetic field and a small amplitude oscillatory shear is studied using numerical simulations. We consider a three-dimensional domain with a single ferrofluid droplet suspended in a non-magnetizable Newtonian fluid. We present results of droplet shape and orientation, viscoelastic functions and bulk emulsion magnetization as functions of the shear oscillation frequency, magnetic field intensity and orientation. We also investigate how the magnetic field induces mechanical anisotropy by producing internal torques in oscillatory conditions. We found that, when the magnetic field is parallel to the shear plane, the droplet shape is mostly independent of the shear oscillation frequency. Regarding the viscometric functions, we show how the external magnetic field modifies the storage and loss moduli, especially for a field aligned to the main velocity gradient. The bulk emulsion magnetization is studied in the same fashion as the viscoelastic functions of the oscillatory shear. We show that the in-phase component of the magnetization with respect to the shear rate reaches a saturation magnetization, at the high frequencies limit, dependent on the magnetic field intensity and orientation. On the other hand, we found a non-zero out-of-phase response, which indicates a finite emulsion magnetization relaxation time. Our results indicate that the magnetization relaxation is closely related to the mechanical relaxation for dilute magnetic emulsions under oscillatory shear.

Nonlinear viscoelasticity and crystallization behavior of anhydrous milk fat/palm stearin/oleogel blends

The crystallization behavior of anhydrous milk fat (AMF)/palm stearin (POs)/diacetyl tartaric acid ester of mono(di)glycerides (DATEM) oleogel blends was investigated, moreover, the linear and nonlinear rheological behavior of systems was analyzed by small amplitude oscillatory shear (SAOS) and large amplitude oscillatory shear (LAOS). The addition of DATEM oleogels inhibited the growth rate of crystals of blends at 4 °C and reduced the average size of crystalline nanoplatelet. Moreover, the DATEM oleogels promoted the transition of blends to more stable β polymorphism. The nonlinear rheological response of blends was qualitatively analyzed by normalized Lissajous-Bowditch curves. The addition of DATEM oleogels made blends more resistant to large deformations and slowed down viscous losses while reducing the rearrangement behavior of the crystal microstructure under high strain. These findings could open up the possibility of developing low-saturated fat products and further broaden the application of oleogels.

Rod-climbing rheometry revisited.

The rod-climbing or "Weissenberg" effect in which the free surface of a complex fluid climbs a thin rotating rod is a popular and convincing experiment demonstrating the existence of elasticity in polymeric fluids. The interface shape and steady-state climbing height depend on the rotation rate, fluid elasticity (through the presence of normal stresses), surface tension, and inertia. By solving the equations of motion in the low rotation rate limit for a second-order fluid, a mathematical relationship between the interface deflection and the fluid material functions, specifically the first and second normal stress differences, emerges. This relationship has been used in the past to measure the climbing constant, a combination of the first (Ψ1,0) and second (Ψ2,0) normal stress difference coefficients from experimental observations of rod-climbing in the low shear rate limit. However, a quantitative reconciliation of such observations with the capabilities of modern-day torsional rheometers is lacking. To this end, we combine rod-climbing experiments with both small amplitude oscillatory shear (SAOS) flow measurements and steady shear measurements of the first normal stress difference from commercial rheometers to quantify the values of both Ψ1,0 and Ψ2,0 for a series of polymer solutions. Furthermore, by retaining the oft-neglected inertial terms, we show that the "climbing constant"  = 0.5Ψ1,0 + 2Ψ2,0 can be measured even when the fluids, in fact, experience rod descending. A climbing condition derived by considering the competition between elasticity and inertial effects accurately predicts whether a fluid will undergo rod-climbing or rod-descending. Our results suggest a more general description, "rotating rod rheometry" instead of "rod-climbing rheometry", to be more apt and less restrictive. The analysis and observations presented in this study establish rotating rod rheometry combined with SAOS measurements as a prime candidate for measuring normal stress differences in complex fluids at low shear rates that are often below commercial rheometers' sensitivity limits.

Super stable Melaleuca alternifolia essential oil Pickering emulsions stabilized with cellulose nanofibrils: Rheological aspects

Melaleuca alternifolia essential oil (MaEO) has attracted technological interest in the pharmaceutical, cosmetic and food sectors for its outstanding and broad antimicrobial spectra. However, its active components are highly susceptible to oxidation due to weathering. Therefore, stabilization of the MaEO components is essential. In this work, we evaluated the stability and rheology of MaEO-in-water Pickering emulsions using cellulose nanofibrils (CNF) as an eco-friendly and sustainable stabilizing agent. Small amplitude oscillatory shear (SAOS) tests brought exciting information about the relationship between internal microstructure strength and the relaxation processes, retardation processes, and viscous flow behavior of the emulsions. Measurements of oil droplet diameter distribution and steady-state rheological tests indicate that the emulsions have super stability under static environmental conditions within 28 storage days. Also, the emulsions present steady-state viscosity suitable for applications in dysphagic foods, presenting a pronounced shear-thinning behavior appropriate to developing cream and lotion skin-care eco-friendly products for the human body.

Dynamic rheological properties of sesame protein dispersions

AbstractInterest in utilizing new sustainable protein sources is increasing, and understanding the rheological behavior of sesame protein can be useful in further application. Small amplitude oscillatory shear measurements of sesame protein dispersions at varying concentrations of 5.0%, 7.5%, and 10.0% were examined at both linear and nonlinear regions. Although the sesame protein dispersions showed pseudoplastic behavior, the shear‐thickening effect of sesame proteins at higher concentrations makes it possible to apply in beverages without increasing viscosity. The low values of the yield point of the sesame protein explained its feasibility for utilization in varying products such as high‐protein‐enriched beverages without the adverse effect of the high viscosity. The fracture stress and strain indicated the high strength of the sesame protein to the mechanical changes. The mechanical properties of the sesame proteins also confirmed typical strong gel behavior. The complex viscosity (η*) was decreased linearly with frequency demonstrating the shear thinning phenomenon. The frequency dependency of the protein was shown a low n value that explains a relatively elastic gel structure. These rheological characteristics of the sesame proteins might be more reliable than the previous works on the static rheological behavior, which provides a new horizon in the application of a sustainable protein in food industries.