Steady Shear Research Articles

Effects of Laminaria japonica polysaccharide and coumaric acid on pasting, rheological, retrogradation and structural properties of corn starch

The aim of this study was to investigate the effects of Laminaria japonica polysaccharide (LJP) and coumaric acid (CA) on pasting, rheological, retrogradation and structural properties of corn starch (CS). Rapid viscosity analysis (RVA) revealed that LJP significantly increased the peak viscosity, trough viscosity, final viscosity, and setback viscosity of CS gel (p < 0.05) in a concentration-dependent manner. The addition of LJP and CA simultaneously caused the pasting of CS to need a greater temperature (from 75.53 °C to 78.75 °C), suggesting that LJP and CA made CS pasting more difficult. Dynamic viscoelasticity measurements found that all gels exhibited typical characteristics of weak gel. When compared to CS gel, 4 % LJP increased the viscosity and fluidity of gel and the simultaneous addition of LJP and CA reduced the elasticity. The steady shear results showed that the all gels were pseudoplastic fluids with shear-thinning behavior. In the meanwhile, the addition of LJP and CA enhanced the pseudoplasticity of CS-LJP-CA gel and improved its shear thinning. Furthermore, thermodynamic results showed that 8 % LJP promoted the retrogradation of CS gel and 2.0 % CA delayed the retrogradation of CS gel. Notably, on the 7th day of retrogradation, 2.0 % CA significantly decreased the retrogradation rate of CS-LJP by 19.31 % as compared to CS + 8 % LJP. Microstructure observation revealed that LJP made the honeycomb network structure of CS gel partially collapsed, and the surface of CS-LJP gel developed venation. Nevertheless, the structure of CS-LJP gel was clearly enhanced by adding CA. FT-IR spectra demonstrated that the addition of LJP or CA to CS did not result in the formation of a new distinctive peak in the system, suggesting the absence of a new group. Moreover, LF-NMR findings showed that LJP and CA strengthened the gel structure of CS and enhanced its capacity to retain water. This study not only provided a new insight into using LJP and CA to regulate the gel properties of CS, but also provided scientific strategy for developing starchy foods.

Effects of Ultrasonic Power on the Structure and Rheological Properties of Skin Collagen from Albacore (Thunnus alalunga).

The effects of ultrasonic power (0, 150, 300, 450, and 600 W) on the extraction yield and the structure and rheological properties of pepsin-soluble collagen (PSC) from albacore skin were investigated. Compared with the conventional pepsin extraction method, ultrasonic treatment (UPSC) significantly increased the extraction yield of collagen from albacore skin, with a maximum increase of 8.56%. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed that peptides of low molecular weight were produced when the ultrasonic power exceeded 300 W. Meanwhile, secondary structure, tertiary structure, and X-ray diffraction analyses showed that the original triple helix structure of collagen was intact after the ultrasonic treatment. The collagen solutions extracted under different ultrasonic powers had significant effects on the dynamic frequency sweep, but a steady shear test suggested that the collagen extracted at 150 W had the best viscosity. These results indicate that an ultrasonic power between 150 and 300 W can improve not only the extraction yield of natural collagen, but also the rheological properties of the collagen solution without compromising the triple helix structure.

Particle size and concentration of ground rice on tribological properties and in vitro starch digestibility of rice porridge

ABSTRACT Rice porridge is a food for general consumption; however, it may vary in food texture and starch digestibility depending on particle sizes and concentrations. This study investigated the tribological properties, steady shear flow, and in vitro starch digestibility of rice porridge with different particle sizes of ground rice (small size, <0.2 mm; large size, 0.2–0.45 mm; based on sieving) and concentrations (5, 7.5, or 10% w/v). The results showed that a high concentration of large-sized ground rice promoted lubrication properties, with the maximum friction coefficient reducing from ~ 0.7 in the 5% w/v concentration to ~ 0.4 in the 10% w/v concentration. In addition, the reduction in the friction started at a sliding speed of ~ 2 mm/s for the high concentration ground rice compared to ~ 20 mm/s for the low concentration rice. The results of high viscosity, small hysteresis loops, and swollen rice particles under morphological observation showed greater porridge stability for the high concentration, thus promoting its lubrication properties. These physical characteristics of the porridge could also play a role in starch digestibility during in vitro gastric digestion. Therefore, the management of ground rice to obtain a large size and a high concentration in rice porridge could benefit food preparation for the elderly and people having difficulty swallowing.

A comparison between the FENE-P and sPTT constitutive models in large-amplitude oscillatory shear

The finitely extensible nonlinear elastic with Peterlin closure (FENE-P) and simplified Phan-Thien–Tanner (sPTT) viscoelastic models are used widely for modelling of complex fluids. Although they are derived from distinct micro-structural theories, these models can become mathematically identical in steady and homogeneous flows with a particular choice of the values of the model parameters. However, even with this choice of parameter values, the model responses are known to differ from each other in transient flows. In this work, we investigate the responses of the FENE-P and sPTT constitutive models in large-amplitude oscillatory shear (LAOS). In steady shear, the shear stress scales with the non-dimensional group $Wi/(aL)$ ( $Wi\,\sqrt {\epsilon }$ ) for the FENE-P (sPTT) model, where $Wi$ is the Weissenberg number, $L^2$ is the limit of extensibility in the FENE-P model ( $a$ being $L^2/(L^2-3)$ ), and $\epsilon$ is the extensibility parameter in the sPTT model. Our numerical and analytical results show that in LAOS, the FENE-P model shows this universality only for large values of $L^2$ , whereas the sPTT model shows it for all values of $\epsilon$ . In the strongly nonlinear region, there is a drastic difference between the responses of the two models, with the FENE-P model exhibiting strong shear stress overshoots that manifest as self-intersecting secondary loops in the viscous Lissajous curves. We quantify the nonlinearity exhibited by each constitutive model using the sequence of physical processes framework. Despite the high degree of nonlinearity exhibited by the FENE-P model, we also show using fully nonlinear one-dimensional simulations that it does not shear band in LAOS within the range of conditions studied.

Temperature dependence of mechanical strength in HPDC Mg–6Y–3Zn–1Al alloy with LPSO phase

The temperature dependence of mechanical strength including yield strength (YS) and ultimate tensile strength (UTS) in HPDC WZA631 alloy is investigated in a wide temperature range from room temperature (RT) to 350 °C. It is found that at 25–300 °C, YS and UTS do not drop markedly, from 173 MPa and 274 MPa at RT to 113 MPa and 170 MPa at 300 °C, respectively. While above 300 °C the flow stress falls rather rapidly, to 74 MPa for YS and to 108 MPa UTS at 350 °C. The (Al,Zn)2Y phase exhibits similar behavior between 150 °C and 350 °C, breaking up under stress and becoming the relatively stable crack source without catastrophic cracking. The LPSO phase, keeping steady and excellent critical resolved shear stress (CRSS) below 250 °C, remains unchanged with complete network structure at 150 °C and 250 °C. Therefore, the LPSO phase reinforces the alloy with slow flow stress reduction at RT-300 °C for WZA631 alloy. The tensile property deteriorates above 300 °C due to the destruction of the network structure as well as the reduction of CRSS for the prismatic slip of LPSO under tensile loading. Thus, the LPSO phase determines the mechanical strength evolution of WZA631 alloy, which is similar to the behavior of γ’ phase in the Ni-based superalloys. Besides, the relationship between strength and temperature is described by the Arrhenius equation, which may be reduced to an exponential model in the form of σ=a+bT for HPDC WZA631 alloy.

On rheological properties of disc-shaped cellulose nanocrystals

The rheological properties of a substance depend greatly on its morphology, and rod-shaped cellulose nanocrystals (RCNCs) and cellulose nanofibrils (CNFs) have been extensively studied for their rheological properties. Nevertheless, the rheological properties of disc-shaped cellulose nanocrystals (DCNCs) with crystalline allomorph II derived from mercerized cellulose remain unknown yet. This work investigated the DCNCs' rheological properties in depth using steady-shear and oscillation measurements. At the same concentration, DCNC's suspension viscosity is lower than that of RCNC; RCNC has an instinct viscosity of 258.2, while DCNC has 187.9. Comparing RCNC suspensions with cellulose nanorods, DCNC has a lower aspect ratio and exhibits a distinct steady shear behavior. Under polarized film, DCNC suspension cannot self-assemble into chiral or liquid crystal phases, and with increasing concentrations, the system transitions from an isotropic phase to a gel phase. Oscillation sweeps demonstrate that the gel transition occurs at 7 %–8 %. Based on thixotropic recovery sweep outcomes, the high-stress oscillations enhance the network structure of DCNC suspensions, which is significantly different from that of RCNC suspensions. Results demonstrate the unique properties of DCNC, highlighting its application as a rheological modifier.

Development of “clean label” gluten-free breads fortified with flaxseed slurry and sesame cake: Implications on batter rheology, bread quality and shelf life

Following the recently emerged trends for products without additives and valorization of food processing by-products, “clean label” gluten-free (GF) breads were developed using a flaxseed slurry (FS) at 3% or 4.5% level (flaxseed basis), instead of the commonly used structurant in GF doughs, methylcellulose, and 3 or 6% (flour mixture basis) sesame cake (SC) for further product nutritional improvement. These alternative ingredients increased batter hardness and cohesiveness (back extrusion test) as well as elastic modulus, complex and steady shear viscosity (rheometry), compared to formulation containing only methylcellulose (control). The fortified breads had lower loaf specific volumes, than the control, but significantly higher than a GF bread made without any added hydrocolloid. FS and SC enhanced the formation of β-sheet structures (FTIR spectroscopy) in the batter and bread protein matrix. FS breads exhibited similar crumb hardness, cohesiveness, and springiness (TPA test) with the control, whereas inclusion of SC compromised these textural attributes. Nevertheless, the latter samples showed less pronounced textural changes upon storage (25°C-48 h), with similar extent of staling to control. For the fortified stored breads, there were no significant changes in protein conformation, compared to fresh products, whereas crumb starch retrogradation (calorimetry-DSC) was lower than the control. Additionally, the FS and SC increased the protein and dietary fiber contents and introduced nutty and sesame-like flavor notes to the breads, leading to improved overall acceptability scores. Overall, FS and SC seemed to be promising functional ingredients for the development of “clean label” GF breads with enhanced quality and shelf life.

Thermally activated intermittent flow in amorphous solids.

Using mean field theory and a mesoscale elastoplastic model, we analyze the steady state shear rheology of thermally activated amorphous solids. At sufficiently high temperature and driving rates, flow is continuous and described by well-established rheological flow laws such as Herschel-Bulkley and logarithmic rate dependence. However, we find that these flow laws change in the regime of intermittent flow, where collective events no longer overlap and serrated flow becomes pronounced. In this regime, we identify a thermal activation stress scale, xa(T,), that wholly captures the effect of driving rate  and temperature T on average flow stress, stress drop (avalanche) size and correlation lengths. Different rheological regimes are summarized in a dynamic phase diagram for the amorphous yielding transition. Theoretical predictions call for a need to re-examine the rheology of very slowly sheared amorphous matter much below the glass transition.

Effect of rotational shear on the dielectric dispersion of a nematic liquid crystal above the Freedericksz threshold field.

Rheo-dielectric studies of soft materials provide important information on the dynamic structure and electric polarization. We study the dielectric dispersion of a nematic liquid crystal by applying a high AC probe field without a DC bias and a low AC probe field with a high DC bias under steady rotational shear. The dielectric anisotropy of the nematic is positive and the applied electric field is parallel to the velocity gradient with a magnitude larger than the Freedericksz threshold field. We find that the dielectric dispersion and the relaxation frequencies are strongly shear rate dependent. The analysis of the results based on a simple physical model shows that the effective dielectric constant of the nematic with non-uniform director tilt in the shear plane can be modelled as a series combination of parallel and perpendicular components. Our experiments demonstrate changes in dielectric dispersion are due to molecular reorientation under the influence of the competing effects of hydrodynamic and dielectric torques.

Heterogeneity-induced retraction in viscoelastic fluids following cessation of flow.

Complex fluids including colloidal suspensions, microgels, and entangled wormlike micelles (WLMs) can develop heterogeneous flow regions under imposed steady shear. In some of these systems, the evolution to this flow state from rest is accompanied by flow reversal - when a portion of the fluid moves opposite to the imposed flow direction. Flow reversal was proposed to occur in shear startup when (1) the fluid has significant elasticity, and (2) the flow becomes heterogeneous immediately following the stress overshoot [McCauley et al., J. Rheol., 2023, 67, 661-681]. To verify this hypothesis, a new method is developed for measuring flow heterogeneity. Upon cessation of the imposed flow, elasticity and flow heterogeneity cause retraction of the fluid, which is quantified with particle tracking velocimetry. Flow is stopped at key times during shear startup in two systems: a gel-like WLM that exhibits flow reversal before heterogeneous flow and a viscoelastic, fluid-like WLM that does not. The degree of flow heterogeneity is inferred from the shape and magnitude of velocity profiles measured during retraction. Flow heterogeneity develops earlier in gel-like WLMs - supporting the proposed flow reversal criteria. For comparison, heterogeneous Couette flows described with the upper-convected Maxwell or Germann-Cook-Beris models are analyzed. These theoretical flow problems confirm that stark differences in rheological properties across the flow geometry can cause significant fluid retraction and reproduce key features of the experimentally observed retraction. This new method can be used to extract quantitative information about spatially heterogeneous flows in viscoelastic complex fluids, whether or not flow reversal occurs.

Rheology of paste-like food inks for 3D printing: Effects of nutrient and water content

This research delves into understanding the effects of composition on the rheological response of multi-component food inks for 3D food printing. Accordingly, the motivation is to decouple the nutrient and water content effects on the rheology. We formulated inks by combining pea fractions with water and employing a water-holding-capacity based hydration method. Rheology is characterized by steady shear rate and oscillatory strain amplitude sweeps. Strain sweep curves infer that the deformation response of all inks follows a similar trend, and samples sharing the same macronutrient formulation are mapped to a master curve after scaling with the elastic plateau modulus. Samples sharing the same macronutrient formulation mapped to a master curve after scaling with the elastic modulus. Shear rate testing showed that the inks were shear thinning yield stress materials. Shear rate sweeps also collapsed on a master curve scaled by the yield stress and critical shear rate on the y and x axes. The yield stress and the plateau modulus appeared to be controlled by the water content, while the shear and strain thinning exponents were independent of the formulations, inferring that the rheology is scaled by the water content while preserving the shear thinning response. Observing the independence of the rheological properties from the nutrient composition and scalability of the rheology by the water content provided a step forward in developing formulations with various nutrient content at desired ow properties, which promises personalized nutrition. Furthermore, the study shows the applicability of various rheological techniques, which are expected to contribute to the literature on the rheology of granular pastes.

Laun's rule for predicting the first normal stress coefficient in complex fluids: A comprehensive investigation using fractional calculus

Laun's rule [H. M. Laun, “Prediction of elastic strains of polymer melts in shear and elongation,” J. Rheol. 30, 459–501 (1986).] is commonly used for evaluating the rate-dependent first normal stress coefficient from the frequency dependence of the complex modulus. We investigate the mathematical conditions underlying the validity of Laun's relationship by employing the time-strain–separable Wagner constitutive formulation to develop an integral expression for the first normal stress coefficient of a complex fluid in steady shear flow. We utilize the fractional Maxwell liquid model to describe the linear relaxation dynamics compactly and accurately and incorporate material nonlinearities using a generalized damping function of Soskey–Winter form. We evaluate this integral representation of the first normal stress coefficient numerically and compare the predictions with Laun's empirical expression. For materials with a broad relaxation spectrum and sufficiently strong strain softening, Laun's relationship enables measurements of linear viscoelastic data to predict the general functional form of the first normal stress coefficient but often with a noticeable quantitative offset. Its predictive power can be enhanced by augmenting the original expression with an adjustable power-law index that is based on the linear viscoelastic characteristics of the specific material being considered. We develop an analytical expression enabling the calculation of the optimal power-law index from the frequency dependence of the viscoelastic spectrum and the strain-softening characteristics of the material. To illustrate this new framework, we analyze published data for an entangled polymer melt and for a semiflexible polymer solution; in both cases our new approach shows significantly improved prediction of the experimentally measured first normal stress coefficient.

Rheology of bi-disperse dense fiber suspensions.

While significant progress has been made in the modeling and simulation of uniform fiber suspensions, no existing model has been validated for industrially-relevant concentrated suspensions containing fibers of multiple aspect ratios. In the present work, we investigate bi-disperse suspensions with two fiber populations in varying aspect ratios in a steady shear flow using direct numerical simulations. Moreover, we measure the suspension viscosity by creating a controlled length bidispersity for nylon fibers suspended in a Newtonian fluid. The results showed good agreement between the experimentally measured and numerically predicted viscosity for bi-disperse suspensions. The ratio between the aspect ratio of large to small fibers (size ratio) and the volume fraction of large fibers (composition) in bi-disperse systems strongly affected the rheological behavior of the suspension. The increment of relative viscosity associated with size ratio and composition can be explained by the decrease in the maximum flowable limit or jamming volume fraction. Moreover, the relative viscosity of bi-disperse suspensions collapses, when plotted against the reduced volume fraction, demonstrating the controlling influence of the jamming fraction in bi-disperse fiber suspensions.

Physicochemical, Structural and Rheological Properties of Hawthorn Yam (Dioscorea rotundata) Flour

Hawthorn yam has been widely used for the development of food products. The objective of the present work was to investigate the physicochemical, structural, and rheological properties of hawthorn yam flour (CHYF). The identification of chemical composition by proximal and Fourier Transform Infrared Spectroscopy (FTIR) analysis; the morphological by Scanning Electron Microscope (SEM) and rheological properties by steady shear test, stress test, frequency sweep, temperature sweep, and pasting properties analysis were done. CHYF presents a high carbohydrate content (80.47 ± 1.14%), followed by the protein content (8.76 ± 0.58%), ash (3.56 ± 0.52%), and the lowest fat content (0.39 ± 0.06%), and different functional groups such as C=O, COO, N–H, and O-H. Flour particles present a particle size between 27 and 43µm, with spherical-oval morphology with a smooth surface. Flours present a non-Newtonian fluid shear-thinning adjusted to the Power Law model (R2 &gt; 0.99), and a characteristic of a typical strong gel material with a storage modulus (G^') higher than loss modulus (G^'') and paste temperature of 81.6 ° C with a Peak Viscosity (PV) of 750 cP. Then, it is a potential source of natural ingredients with technological properties for the food industry and the food sovereignty of many countries in the world.

Manufacturing of emulsion type garlic paste: Characterization of rheological properties as affected by lecithin, guar gum, and olive oil using steady, dynamic, and three interval thixotropy tests

AbstractThe objective of this work was to investigate the steady, dynamic mechanical properties, and 3 interval thixotropy test (3 ITT) characterization of emulsion type garlic paste prepared with different concentrations of lecithin, guar gum, and olive oil. A three factor and three level Box Behnken design of response surface methodology was used to specify the physicochemical, steady shear, viscoelastic and deformation and recovery properties (applying 3 ITT) of paste. Garlic paste samples showed non‐Newtonian shear thinning behavior and Herchel–Bulkley model was fitted to the data satisfactorily (R2 &gt; 0.85). Dry matter contents were in the range of 37.13%–41.14% depending on the processing variables. Dynamic mechanical spectrum showed that the garlic paste was weak gel having dominant viscous behavior compared to elastic behavior. Three interval thixrotropy test showed that the samples showed partial recovery after deformation due to the weak gel like character. Optimization showed that the maximum consistency (114.6 Pa sn) would be at 2.11 g lecithin, 0.11 g guar gum and 14.96 mL olive oil while the minimum value (49.16 Pa sn) would be at 1.02 g lecithin, 0.11 g guar gum, and 5.81 mL olive oil. Overall, the findings of this investigation revealed that the physicochemical and rheological characteristics of garlic paste can be significantly influenced by the concentrations of lecithin, guar gum, and olive oil. It is crucial to carefully select the appropriate concentration levels to achieve the desired quality of garlic paste.Practical applicationsGarlic is one the most popular vegetables consumed by the people due to its characteristic taste and aroma. Because of its functional properties, garlic is also used as an additive for food formulation. In this study, garlic is used for the production of garlic paste which could be used for food formulations as a taste enhancer or salad aromatizer. Accurate and dependable rheological data play a crucial role in designing flow processes, assessing the deformation and recovery rates of substances during various engineering operations and preparation of new food formulations. In this context, we developed a predictive model by response surface methodology which estimates physico‐chemical and rheological properties of garlic paste samples. Therefore, this study holds significant importance in terms of estimating the physicochemical and rheological properties of garlic paste for food manufacturers.

Extrapolation of classical rheometry of plant protein pastes to extrusion conditions

This study explores alternative methods to measure the rheology of pastes based on soy and pea proteins, which are commonly used as starting material in extrusion for the preparation of meat analogs. Currently, it is still a challenge to obtain consistent rheological data on such materials for steady shear at conditions that are relevant for the extrusion of such systems. Hence, possibilities are explored for the extrapolation of results obtained with classical rheometers operating at temperatures below boiling point, to conditions that are relevant for the extrusion of such systems. The above was combined, with findings from off-line and in-line capillary rheometers, which can provide steady shear measurements above boiling point and at hydration levels as used in extrusion.We have analysed the consistency of our new results with previous oscillatory shear measurements, performed at conditions similar to those of meat analog extrusion. For validation of the extrapolation we have analysed whether the new rheology data follow similar scaling rules. As classical rheometers can handle only moderate torques, the measurements are limited to hydration levels higher than those used in extrusion (75–85%). Despite this limitation, strain sweeps with classical rheometers show that in this regime the elastic modulus also scales with Tg/T, the ratio of glass transition, and actual temperature. Yet, its dependency on Tg/T appears differently from measurements performed at extrusion-like conditions. Moreover, our current results indicate a strong thixotropic nature of plant protein pastes at temperatures below boiling point. Consequently, flow curves are only stable if performed from high to low shear rates. Nevertheless, our data can be mapped to a single master curve following the Herschel-Bulkley model, with parameters also following a scaling rule dependent on Tg/T.This Tg/T scaling is used to construct master curves with data from the off-line and in-line capillary rheometers. The obtained shift factors for the flow curves are in agreement with old literature data obtained for SPI, but they deviate significantly from our steady shear measurements with classical rheometers. Based on the results of our current and previous study we have a critical, general discussion on the possibility of extrapolation of classical rheometry of plant protein pastes to process conditions used for production of meat analogs.

Shear-induced flow and dynamics of the nematic phase of Sunset Yellow lyotropic chromonic liquid crystal

ABSTRACT Fundamental understanding of rheological properties of lyotropic chromonic liquid crystals is inadequate compared to their thermotropic counterparts in spite of the growing interest in these materials. Here, we investigate the rheological properties of a lyotropic chromonic nematic liquid crystal (LCLC), prepared by dissolving 32 wt% of Sunset Yellow (SSY) in water. The flow curves (stress-strain rate, σ − γ ˙ ) at different temperatures exhibit three flow regimes R1, R2 and R3, respectively. At room temperature, in R1 ( γ ˙ < γ ˙ cl ) and R3 ( γ ˙ > γ ˙ cu ) the sample exhibits Newtonian flow behaviour ( σ ∝ γ ˙ ), whereas, in R2 ( γ ˙ cl < γ ˙ < γ ˙ cu ), it shows a power-law dependence ( σ ∼ γ ˙ β ). With increasing shear rate the change of stress from R1 to R2 is continuous, whereas the change is discontinuous from R2 to R3. We observe stress fluctuations under steady shear in regime R2 similar to those reported in worm-like micellar systems and in thermotropic twist-bend nematic liquid crystals. The non-monotonic flow behaviour and the stress dynamics are corroborated using in situ rheo-microscopy.

Rheological Characterization of Gofio and Aloe Vera Blended Juice

Considering that gofio (Gf) and aloe vera juice (AVJ) have very good nutritional qualities, their combination is proposed because it is indicated as an easy and fast source of basic bio-elements. The texture of a food must be accepted by customers. This means that the rheological characteristics of the product must be known and controlled. Therefore, the influence of Gf concentration on the rheological behavior of Gf/AVJ suspensions must be determined. With continuous shear experiments, the purely viscous response of a material can be obtained. AVJ and Gf/AVJ suspensions showed shear-thinning behavior. The ability of Gf particles and aggregates to distort the flow field was quantified determining the intrinsic viscosity η of the suspensions at several shear rates using Krieger–Dougherty equation. The results indicated that the shape and size of Gf aggregates is not affected by the mechanical action due to shear. The power law (Ostwald–de Waele) model fitted the experimental steady viscosity versus shear rate values (steady viscosity curves). The flow index was less than 1, which corresponded to shear-thinning behavior. It was obtained that the flow index of AVJ maintained unaltered despite the presence of Gf particles. However, the viscosity value increased with the increasing amount of Gf as it was expected. The viscoelastic behavior of the microstructure at rest of the AVJ and Gf/AVJ suspensions was studied using oscillatory shear tests. First, linear viscoelastic response was confirmed in the relatively low amplitude shear region γ0&lt;0.001 using an amplitude sweep shear test. After that, frequency sweep shear tests were conducted in the region where Gf/AVJ suspensions showed linear viscoelastic behavior. Varying the frequency, the response of the microstructure at rest of the suspensions when the mechanical action lasts from short to long time interval can be characterized. Jeffreys mechanical model was used for the analysis of the LVE response of Gf/AVJ suspensions. Using small amplitude oscillatory shear (SAOS) tests, it was obtained that Gf/AVJ suspensions are viscoelastic liquids that change their texture from chewy to creamy when the Gf concentration increases.

Thixo-elastoviscoplastic modeling of human blood

We propose an enhanced model for the rheological characterization of human blood that accounts for thixotropy, viscoelasticity, and yield-stress. Blood plasma is assumed to act as a Newtonian solvent. We introduce a scalar variable, λ, to macroscopically describe the structure of blood. The temporal evolution of λ is governed by an equation that accounts for aggregation of red blood cells and breakdown of rouleaux structures. We introduce a Gaussian function that qualitatively describes experimental findings on rouleaux restructuring and the expression that was proposed by Stephanou and Georgiou for the breakdown term. The constitutive equation for stresses is based on the elastoviscoplastic formalism by Saramito. However, the max term of the viscoplastic deformation rate has been replaced by a continuous function of λ to account for smooth solid-fluid transition, following the experimental evidence. The continuous yielding description provides improved rheological predictions, especially in small amplitude oscillatory shear. The model predicts finite viscous dissipation at small amplitude oscillation, as we would expect from a gel material-like human blood. Overall, it has nine adjustable parameters that are fitted simultaneously to experimental data by nonlinear regression. The model can accurately predict numerous flow conditions: steady shear, step shear, hysteresis loops, and oscillatory shear. We compare this model (TEVP 9) to our previous formulation for human blood (TEVP 11), and we show that the predictions of the new model are more accurate, despite using fewer parameters. We provide additional predictions for uniaxial elongation, which include finite normal stress difference, extensional hardening at large values of the extensional rate, and extensional thinning at extremely large extensional rates.

Shear-DSC study on the crystal-isotropic phase transition of semidilute aqueous cetyltrimethylammonium bromide (CTAB) solutions

A differential scanning calorimeter equipped with a steady shear flow system (Shear-DSC) was developed, and the effects of shearing on the crystal-isotropic phase transition were investigated for aqueous cetyltrimethylammonium bromide (CTAB) solutions at 4, 18, and 26 wt%. At 18 wt%, where rod-like micelles are formed in the isotropic phase, the transition temperature Ttrs changes with the shear rate γ˙. At low shear rate (γ˙<1s−1), Ttrs decreases as γ˙ increases due to an increase in the surface energy of the crystal grains. At high shear rate (γ˙>30s−1), Ttrs increases as γ˙ increases because of the orientational ordering of rod-like micelles induced by shearing in the isotropic phase, leading to the formation of a nematic structure. The latter change is suppressed for the solution at 26 wt% because the nematic phase is formed without shearing, whereas it disappears at 4 wt% indicating that the spherical micelles are not deformed by shearing.