Steady Shear Flow Research Articles

Polyacrylamide Grafted Xanthan: Microwave-Assisted Synthesis and Rheological Behavior for Polymer Flooding.

Application of polymer-flooding systems in secondary and tertiary oil recovery represents a real challenge for oil industry. In this work, our main objective is to explore possibilities of making use of xanthan-g-polyacrylamide for polymer flooding in a particular Devonian oilfield of medium salinity. The graft polymer was synthesized by using microwave-assisted graft copolymerization reaction of acrylamide on xanthan. The synthesized copolymer with optimized grafting parameters has been characterized by Infrared Spectroscopy and Thermal Analysis (DSC). Rheological analysis by steady shear and oscillatory flow experiments have been subsequently performed for xanthan and grafted xanthan under reservoir conditions. In steady shear, as expected the grafted polymer solutions flow as shear-thinning materials and apparent viscosity showed good fits with Cross’s model. The viscosity losses due to salinity or temperature are more controlled for the grafted xanthan compared to pristine xanthan. When the grafted polymer concentration is increased to 2000 ppm the losses were halved. In oscillatory shear, the copolymer solutions followed a global behavior of semi-dilute entangled systems; furthermore, all dynamic properties were influenced by the brine salinity. Compared to xanthan, the elastic properties of xanthan-g-polyacrylamide solutions have been significantly improved in saline media and the losses in elasticity of grafted polymer solutions are lower.

Steady and Oscillatory Shear Flow Behavior of Different Polysaccharides with Laponite®.

The rheological behavior, in terms of steady and oscillatory shear flow, of Laponite® with different polysaccharides (alginate, chitosan, xanthan gum and levan) in salt-free solutions was studied. Results showed that a higher polymer concentration increased the zero-rate viscosity and decreased the critical strain rate (Cross model fit) as well as increasing the elastic and viscous moduli. Those properties (zero-rate viscosity and critical strain rate) can be a suitable indicator of the effect of the Laponite® on the shear flow behavior for the different solutions. Specifically, the effect of the Laponite® predominates for solutions with large critical strain rate and low zero-rate viscosity, modifying significantly the previous parameters and even the yield stress (if existing). On the other hand, larger higher polymeric concentration hinders the formation of the platelet structure, and polymer entanglement becomes predominant. Furthermore, the addition of high concentrations of Laponite® increases the elastic nature, but without modifying the typical mechanical spectra for polymeric solutions. Finally, Laponite® was added to (previously crosslinked) gels of alginate and chitosan, obtaining different results depending on the material. These results highlight the possibility of predicting qualitatively the impact of the Laponite® on different polymeric solutions depending on the solutions properties.

Inertial Force Transmission in Dense Granular Flows.

Dense granular flows are well described by several continuum models; however, their internal dynamics remain elusive. This study explores the contact force distributions in simulated steady and homogenous shear flows. The results demonstrate the existence of high magnitude contact forces in faster flows with stiffer grains. A proposed physical mechanism explains this rate-dependent force transmission. This analysis establishes a relation between contact forces and grain velocities, providing an entry point to unify a range of continuum models derived from either contact forces or grain velocity.

Brownian dynamics simulation on orthogonal superposition rheology: Time–shear rate superposition of colloidal gel

The dynamics of model colloidal gels under a steady shear flow is studied by means of a Brownian dynamics (BD) simulation while applying orthogonal superposition rheometry, which superimposes a small amplitude oscillatory flow orthogonal to the main flow direction. Orthogonal dynamic frequency sweep (ODFS) curves are obtained at various magnitudes of the main flow, which shows shear thinning behavior of the colloidal gel. The viscoelastic spectra of the ODFS can be superimposed onto a master curve by the horizontal shift factor, which is equivalent to particle viscosity. That is, the shear rate controls a single master clock for all viscoelastic spectra of the ODFS in the form of a time–shear rate superposition, which bears an analogy with the time–temperature superposition of polymeric systems. In the low-frequency region of the master curve, both orthogonal moduli are well superimposed onto a single master curve, whereas the loss modulus deviates slightly from the master curve in the high-frequency region, which coincides with the experimental findings. We observe spatial and time-varying structural properties in both low- and high-frequency regions on the ODFS curves by decomposing the pair distribution function. It is verified that each flow condition shifted onto the same stress level on the master curve shows identical spatial orthogonal moduli at all radial distances despite the differences in the aggregate size and average particle connectivity.

Comparative study on morphological, rheological and functional characteristics of extruded rice starch citrates and lactates

Two levels of chemically modified starches (starch citrates and lactates) prepared at 20% and 40% w/v concentration was subjected to extrusion to produce pregelatinized starches (PG). Starch citrates and lactates modified at 20% and 40% level were referred as (SC20 and SC40) and (SL20 and SL40), respectively. These PG starches underwent significant structural changes during extrusion as depicted by scanning electron micrographs. Native starches showed lower swelling power and water binding capacity but formed harder gels compared to chemically modified pregels. The dynamic rheology of these polymers (extruded modified starches) suggested visco-elastic property i.e. (G′ > G′′). Citrates demonstrated higher G′ than lactates in both frequency and temperature sweep tests. Stability of storage moduli over entire temperature range confirmed that addition of citrates and lactates led to strengthening of gel structure through cross linking and esterification. Non-newtonian behavior was shown by all samples as determined through steady shear flow test with flow behavior index <1. Starch citrate (SC20-PG) demonstrated higher shear stress values. While, SC40-PG depicted anti-thixotropic behavior as measured through in-shear structural recovery measurements. On the basis of results obtained, the dual modification (chemical followed by extrusion) may impart fruitful applications in various food products.

A review of the second normal-stress difference; its importance in various flows, measurement techniques, results for various complex fluids and theoretical predictions

Shear flow is ubiquitous. Not only is it arguably the most widely-used deformation type to characterise complex fluids in rheological studies but also, in practice, the deformation most likely to occur in the great majority of flows, e.g. involving fluid transport through pipes or conduits. In steady simple shear flow the rheological properties of a complex fluid are completely characterised in just three material functions; the variation with shear rate of the shear viscosity and the so-called first and second normal-stress differences. Despite requiring only three material functions to be completely characterised, most shear-flow rheological characterisations are usually restricted simply to the shear viscosity and, at best, the variation of the first normal-stress difference N1 with shear rate. The second normal-stress difference N2 remains very much neglected. For dilute polymer solutions where this quantity may be negligibly small in comparison to the first normal-stress difference, such neglect is justified but for a whole range of complex fluids – indeed even polymer solutions outside of the dilute regime and especially melts – it is not clear that N2 may be safely disregarded. Indeed, in this review article we spotlight a number of flows where second normal-stress differences are of importance and potentially major consequence. Following this attention, we review the many experimental techniques which have been proposed for its measurement and survey the available literature for measurements of this quantity for various complex fluids including the aforementioned polymeric solutions, melts, liquid crystals, dense non-Brownian suspensions (both with Newtonian and complex fluid bases), semi-dilute wormlike micellar fluids and magnetorheological fluids. Theoretical predictions for N2 from various commonly-used continuum constitutive equations – primarily from the polymer literature – are also given and their asymptotic predictions at low and high shear rates compared. Finally, we end with a brief summary and outlook.

Correlations in rheological behavior between large amplitude oscillatory shear and steady shear flow of silica‐filled star‐shaped styrene‐butadiene rubber compounds: Experiment and simulation

AbstractThe large amplitude oscillatory shear (LAOS) and steady shear behavior of star‐shaped SSBR/silica 60 phr (21 vol%) compounds with various filler surface areas was measured and simulated. An SBR gum and SBR compounds containing four different silicas with surface areas of 55, 135, 160, and 195 m2/g were utilized. Rheological behavior indicated clear correlation with surface area. LAOS tests showed an increase in dynamic moduli, shear stress, and higher order harmonic contributions with surface area. Elastic and viscous Lissajous figures showed significant distortion at intermediate and higher strain amplitudes. Additionally, ratios of third and fifth order stress harmonics to the first stress harmonic (I3/1 and I5/1, respectively) showed a ''bump'' at intermediate strain amplitudes for the three highest surface area compounds. With regards to steady shear, all materials showed strong shear thinning behavior, and an increase in shear viscosity with surface area. The Cox‐Merz rule was shown to be valid for the SBR gum but not for the filled compounds. However, the complex viscosity as a function of shear rate amplitude at various frequencies at high strain amplitudes and the steady shear viscosity as a function of shear rate coincided. This correlation, referred to as the Philippoff approach, has important ramifications for the rubber industry, providing quick data for predicting processing behavior. The Simhambhatla‐Leonov model was successfully employed to simulate rheological behavior for the SBR gum and the lowest surface area silica compound, but the model yielded mixed results for the higher surface area silica compounds.

Factors influencing the adhesive behavior of carboxymethyl cellulose-based hydrogel for food applications

Carboxymethyl cellulose (CMC) hydrogels have been used as adhesive materials for food and other newly emerged innovative applications. To increase the knowledge of CMC hydrogel-based adhesives and optimize the preparation and storage conditions in practical, we prepared CMC hydrogels for cigar wrapper application and investigated their adhesive performance as affected by different CMC type, concentration, pH, temperature, and storage time, etc. Two parameters, initial adhesiveness and peel strength were used to evaluate the adhesive behavior of CMC with paper and tobacco leaf. Sample C2 with relatively medium molecular weight and medium degree of substitution values showed the best adhesive performance. Hydrogels prepared using boiled water at neutral pH presented better adhesive behavior, which was not significantly affected by storage temperature (up to 13 days). The wettability, steady shear flow behavior, dynamic rheological properties, and stress recovery performance of CMC hydrogel were measured, and their correlations to the adhesive behavior were discussed.

Comprehensive physical visualisation of the chain conformation and solution property of carboxymethylated konjac glucomannan: Comparison of charged and uncharged polyelectrolytes

The present work deals with a comprehensive molecular characterization and delineation of solution property of a series of charged and uncharged carboxymethylated konjac glucomannan (CMKGM) with different molecular weights (Mw, 1.57 × 105–7.33 × 105) and degrees of substitution (DS, 0.19–1.63) by using various rheological models and solution scaling theory. CMKGM macromolecules in aqueous solutions are found to adopt semi-flexible chain conformation and show a tendency close to rigid chains with decreasing Mw and increasing DS. For uncharged CMKGM solutions, the Huggins–Kraemer, Heller, Fuoss and Wolf approaches can achieve equally excellent fitting results for the determination of intrinsic viscosity [η], whereas for charged CMKGM solutions, only the Huggins–Kraemer and Wolf plots are valid. In accordance with the physical scaling law, a scaling relationship exists between rheological parameters and concentration c for salt and salt-free aqueous solutions of CMKGM. The relationship of specific viscosity ηsp ~ c[η] and ηsp ~ c ~ Mw is derived for CMKGM in a high ionic strength environment (NaCl 0.15 M) by using the Kulicke-Keniewske approach. The constitutive models of the linear Maxwell model and two kinds of non-linear PTT and Giesekus models have also been applied to quantitatively describe the rheological properties of CMKGM entangled solutions under either dynamic or steady shear flow.

Phase behavior and rheological properties of basil seed gum/whey protein isolate mixed dispersions and gels.

Many food formulations comprise proteins and polysaccharides simultaneously, contributing in the functional properties in food systems. In this study, the effects of basil seed gum (BSG) addition to whey protein isolate (WPI) dispersions were investigated through phase behavior, steady shear flow, and small amplitude oscillatory shear tests (SAOS). The phase behavior of WPI‐BSG mixed solutions was dependent on the initial concentration of biopolymers, while the effect of BSG was predominant. Herschel–Bulkley model characterized the flow behavior of ternary mixtures, very well. Furthermore, apparent viscosity, the extent of thixotropy and viscoelastic behavior enhanced with increase in BSG concentration, significantly (p ˂ .05). Temperature sweep measurements showed a reduction in WPI gelling temperature by increase in BSG concentration. SEM results depending on BSG concentration revealed the protein continuous, bicontinuous, and polysaccharide continuous networks. Phase separation may be attributed to depletion flocculation and thermodynamic incompatibility of WPI and BSG molecules. The results confirmed the occurrence of phase separation and weak‐gel formation through mixtures, but the rate of gelation was more than the phase separation. In consequence, these results may open up new horizons in developing novel food products and delivery systems as well as utilizing as emulsifying, thickening and gelling agents in food and pharmaceutical industry.

Structure-rheology elucidation of human blood via SPP framework and TEVP modeling

Recent work modeling the rheological behavior of human blood indicates that it has all the hallmark features of a complex material, including shear-thinning, viscoelastic behavior, a yield stress, and thixotropy. After decades of modeling steady state blood data, and the development of simple steady state models, like the Casson and Herschel-Bulkley the advancement and evolution of blood modeling to incorporate more thixo-elasto-visco-plastic (TEVP) features to accurately capture transient flow has renewed interest. With recently collected steady state and oscillatory shear flow rheological data from a DHR-3 using human blood, we show modeling efforts with a contemporary thixo-elasto-visco-plastic (TEVP) model. Best fit rheological model parameters are used to determine values for normal, healthy blood and corroborate correlations from literature. Series of physical processes (SPP) analysis is incorporated to illustrate how mechanical properties are tied to the transient, evolving microstructure of human blood and physiological parameters. Using LAOS data predictions of the structure parameter, λ is compared, and correlated with the transient elastic modulus, G t ′ .

Nonlinear Thermo-Mechanical Full Coupling of Aluminum Oxide Particles Transport in Electrolytic Bath Using Lattice Boltzmann Method

A three-dimensional numerical model has been developed to quantify the predominant phenomena roles on dynamics alumina particles between an electrolytic bath and the vicinity of gas bubbles. At the particle scale, the bath, regarded as turbulent flow, was modeled by a steady plane shear flow and solved using a lattice Boltzmann method. The coupling between the fluid and particle phases is carried out using an immersed boundary method to tackle the interface. This numerical scheme resolves the hydrodynamic perturbation induced by the alumina particles, and hence their interactions are described by Lagrangian particle tracking. The hydrodynamic effects combined with mechanical and thermal responses on the computation of the fluid system's stress intensity factors were investigated. An excellent convergence and accuracy were achieved for the transport and interaction of the alumina particle model.

The relaxation dynamics of single flow-stretched polymers in semidilute to concentrated solutions.

Recent experiments on the return to equilibrium of solutions of entangled polymers stretched by extensional flows [Zhou and Schroeder, Phys. Rev. Lett. 120, 267801 (2018)] have highlighted the possible role of the tube model's two-step mechanism in the process of chain relaxation. In this paper, motivated by these findings, we use a generalized Langevin equation (GLE) to study the time evolution, under linear mixed flow, of the linear dimensions of a single finitely extensible Rouse polymer in a solution of other polymers. Approximating the memory function of the GLE, which contains the details of the interactions of the Rouse polymer with its surroundings, by a power law defined by two parameters, we show that the decay of the chain's fractional extension in the steady state can be expressed in terms of a linear combination of Mittag-Leffler and generalized Mittag-Leffler functions. For the special cases of elongational flow and steady shear flow, and after adjustment of the parameters in the memory function, our calculated decay curves provide satisfactory fits to the experimental decay curves from the work of Zhou and Schroeder and earlier work of Teixeira et al. [Macromolecules 40, 2461 (2007)]. The non-exponential character of the Mittag-Leffler functions and the consequent absence of characteristic decay constants suggest that melt relaxation may proceed by a sequence of steps with an essentially continuous, rather than discrete, spectrum of timescales.

Rheological properties of peanut protein isolate aggregation suspension and acid-induced gel

The dynamic rheological properties of peanut protein isolate (PPI) suspension and acid-induced PPI gels were studied. In frequency sweep test, the storage modulus (G′) and the loss modulus (G″) of PPI aggregation suspensions at different concentrations increased with the increase of frequency. The steady state shear flow test showed that PPI aggregation suspension had a thinning behavior of the shear, and the image of steady shear curve fitted the Carreau model. After gel formation, acid-induced PPI gels showed a typical Type I behavior (strain thinning) in strain sweep test, meaning that PPI gel got easily broken down, and there was a very small opportunity for the protein molecules to re-establish the network. Compared with the strain sweep of PPI aggregation suspensions and gels, the range of the storage modulus existed a dramatic difference, which could get about tenfold. As the frequency increased, both elasticity and viscosity increased in frequency sweep test, which indicated that the frequency dependence of the storage modulus increased with the increase of concentration. Keywords: peanut protein isolate (PPI), aggregation suspension, acid-induced PPI gel, dynamic rheological properties DOI: 10.25165/j.ijabe.20211403.6021 Citation: Huang Z G, Wang X Y, Chi S Y, Hua Z, Bi C H. Rheological properties of peanut protein isolate aggregation suspension and acid-induced gel. Int J Agric & Biol Eng, 2021; 14(3): 255–260.

Точные решения уравнений Обербека – Буссинеска для сдвиговых течений вязкой бинарной жидкости с учетом эффекта Соре

The paper considers an exact solution to the equations of thermal diffusion of a viscous incompressible fluid in the Boussinesq approximation with neglect of the Dufour effect for a steady shear flow. It is shown that the reduced system of constitutive relations is nonlinear and overdetermined. A nontrivial exact solution of this system is sought in the Lin–Sidorov–Aristov class. The resulting family of exact solutions allows one to describe steady-state inhomogeneous shear flows. This class generalizes the classical Couette, Poiseuille, and Ostroumov–Birikh solutions. It is demonstrated that the system of ordinary differential equations reduced within this class retains the properties of nonlinearity and overdetermination. A theorem on solvability conditions for the overdetermined system is proved; it is reported that, when these conditions are met, the solution is unique. The overdetermined system is solvable owing to the algebraic identity relating the horizontal velocity gradients, which are linear functions of the vertical coordinate. The constructive proof of the computation of hydrodynamic fields consists in the successive integration of the polynomials, the polynomial degree being dependent on the values of the boundary parameters.

Method of Viscoelasticity Measurement under Shear-Flow

In anticipation of that direct examination of the shear flow affection on the dynamic viscoelasticity might bring more comprehensive results than the LAOS method, a series of dynamic viscoelasticity measurements with parallel superposition of steady shear flow was planned. The measured values which are function of shear rate ̇γ, that is, storage and loss moduli G′(̇γ), G″(̇γ) and viscosity η(̇γ), are analyzed as three non-dimensional parameters G′(̇γ) / G′(0), G″(̇γ) / G″(0) and η(̇γ) / | η*(ω, ̇γ) |, where η* is complex viscosity. A Couette rheometer ONRH-1b (OhnaTech) was employed, and for the samples, hydroxypropyl cellulose, xanthan gum, carboxyvinyl polymer and C24-hydrophobically modified ethoxylated urethane ware used. All three analyzing parameters show clearly the differences of samples. It is found that the nature of their responses are subjected not by the shear itself, but by the value that divided shear rate with measure frequency (̇γ/ω). On the other hand, it is found that the properties that are subjected by the shear rate do exist. Observation of these results asserts that multifactorial rheological measurement including this superposition method is worthwhile.

Active- and transfer-learning applied to microscale-macroscale coupling to simulate viscoelastic flows

Active- and transfer-learning are applied to microscale dynamics of polymer flows for the multiscale discovery of effective constitutive approximations required in viscoelastic flow simulation. The result is macroscopic rheology directly connected to a microstructural model. Micro and macroscale simulations are adaptively coupled by means of Gaussian process regression (GPR) to run the expensive microscale computations only as necessary. This multiscale method is demonstrated with flows of a polymer solution as a model system. At the microscale level dissipative particle dynamics (DPD) is employed to model the fluid as a suspension of bead-spring micro-structures subjected to steady shear flow. The results yield the non-Newtonian viscosity and the first normal stress difference at strain rates as training data used in a GPR model. DPD parameters are calibrated with respect to experimental data for a real polymer solution. Compliance with these data requires adjustment of the DPD model's cutoff radius, which then becomes a function of the second invariant of the strain rate tensor. The FENE-P model is chosen for the macroscale description using the spectral element method (SEM) to simulate channel flow and flow past a circular cylinder. The DPD results at the lowest possible shear strain rate yield an estimate of the zero-shear rate viscosity, which allows the initiation of the macroscale flow by SEM as a Newtonian fluid. The resulting strain-rate field is surveyed to determine additional shear strain rate sampling points for the DPD system. This new information allows an initial fitting of parameters of the constitutive equation followed by new SEM simulations at the macroscale. Guided by active-learning GPR to select new sampling points, this process continues until convergence is achieved.The effectiveness of this new simulation paradigm for viscoelastic flows is tested with different macroscale operating conditions. The effective closure learned in the channel simulation is then transferred directly to the flow past a circular cylinder at low Reynolds number, where the results show that only two additional DPD simulations are required to achieve a satisfactory constitutive model. With an increase of the Reynolds number, the active-learning scheme automatically detects the inaccuracy of the learned constitutive model, and initiates additional DPD simulations for the extra data needed to once again close the microscale-macroscale coupled system. This new paradigm of active- and transfer-learning for multiscale modeling is readily applicable to other microscale-macroscale coupled simulations of complex fluids and other materials. Furthermore, the coupling between microscale and macroscale solvers can be seamlessly implemented with our open source multiscale universal interface (MUI) library.

Сравнительное изучение кинетики свертывания крови и тромбообразования реологическими и электрореологическими методами.

Цель исследования: изучить механизмы формирования и тромбодинамические свойства кровяного сгустка при тромбообразовании in vitro и представить сравнительное исследование кинетики тромбообразования с помощью реологических и электрореологических методов в условиях постоянного и осциллирующего сдвигового вискозиметрического течения; оценить свертывание цельной и консервированной крови, ее вязкоупругие свой ства и влияние фибриногена и декстранов на формирование сгустка. Материалы и методы. Вязкость и удельную электропроводимость нормальной и консервированной с CPD-A1-адениновым раствором крови измеряли ротационным вискозиметром Low Shear 30 Contraves (LS30) с коаксиальными цилиндрами и копией измерительной системы MS1/1 со встроенными электродами (разработана на базе LS30) в условиях постоянного сдвигового потока и в электрическом поле. Вязкоупругие свойства нормальной цельной крови исследовали с помощью реометра Physica MCR 301 (Anton Paar, Austria) в условиях осциллирующего синусоидального потока. Результаты. Представлены результаты кинетики динамической вязкости и удельной электропроводимости консервированной крови в процессе коагуляции в условиях постоянного сдвигового потока и в электрическом поле. Исследованы вязкоупругие свойства цельной крови в условиях синусоидального осциллирующего вискозиметрического течения и представлены зависимости упругого модуля G' (storage modulus) и модуля потерь G'' (loss modulus), а также нормальных сил как функция времени при свертывании. Приводятся данные эффекта фибриногена и декстрана на упругий модуль G' и на модуль потерь G'' цельной крови в процессе коагуляции. Заключение. В условиях вискозиметрического течения при низких скоростях сдвига кинетика тромбообразования характеризуется начальным этапом постепенного увеличения кажущейся вязкости и уменьшения удельной электропроводимости крови и периодом интенсивной коагуляции, характеризирующимся экспоненциальным ростом вязкости и параллельным уменьшением удельной электропроводимости исследуемого образца. Установлено, что коагулирующая цельная кровь обладает нелинейными вязкоупругими свойствами. Кинетика образования сгустка в условиях осциллирующего вискозиметрического течения крови характеризуется увеличением упругого модуля G' и модуля потерь G'' со временем. Одновременно зарегистрирована и отрицательная нормальная сила исследуемого образца в зазоре между пластинами при постоянной толщине зазора. Повышение содержание фибриногена ускоряет коагуляцию и увеличивает значения упругого модуля G' и модуля потерь G'', а также и нормальной силы коагулирующей цельной крови. Objectives: to study the mechanisms of thrombus formation and thrombodynamic properties of a blood clot during coagulation in vitro and to present a comparative study of clot kinetics formation under conditions of steady and oscillating shear viscometric flow and at electric field by rheological and electrorheological methods; to evaluate the coagulation of whole and preserved blood, its viscoelastic properties and the effect of fi brinogen and dextrans on clot formation. Materials/ Methods. The viscosity and electrical conductivity of normal blood and blood preserved with CPD-A1-adenine solution were measured with a Low Shear 30 Contraves (LS30) rotational viscometer with coaxial cylinders and with a copy of the measuring system MS1 / 1 with builtin electrodes at a steady viscometric shear flow and in an electric field too. The viscoelastic properties of normal whole blood were investigated using a Physica MCR 301 rheometer (Anton Paar, Austria) at an oscillating sinusoidal flow. Results. Kinetics of the dynamic viscosity and electrical conductivity of preserved blood during coagulation at a steady shear flow and at electric field were obtained. The viscoelastic properties of whole blood were investigated under conditions of sinusoidal oscillating viscometric flow. The dependences of the elastic (storage) modulus G' and the loss modulus G'', as well as the normal coagulation forces as a function of time are presented. The effect of fibrinogen and dextran on the elastic modulus G' and the loss modulus G'' of whole blood during coagulation are presented. Conclusions. The kinetics of blood coagulation at low shear rates is characterized by a gradual increase of the apparent viscosity and a decrease in blood conductivity at the initial stage and an exponential increase in viscosity during intensive coagulation and a parallel decrease of conductivity too. It was established that coagulating whole blood exhibit nonlinear viscoelastic properties under conditions of sinusoidal blood flow. The kinetics of thrombus formation is characterized by increasing the elastic modulus G' (storage modulus) and the loss modulus G'' with time. The negative normal force in the gap between the plates is also registered at a constant thickness of the gap. An increase in fibrinogen content accelerates coagulation and increases the values of elastic modulus G' and loss modulus G', as well as of the normal force of coagulating whole blood.

Evaluation of mechanical properties of different asphalt concrete types in relation with mixing and compaction temperatures

The Equiviscous (ASTM D2493) procedure for determining mixing and compaction temperatures of asphalt mixtures was built and developed for unmodified bitumen mixtures. The implementation of this procedure often requires heating of modified bitumen to excessive temperatures that can potentially damage asphalt mixtures. To overcome such issues, highway agencies and modifier suppliers generally predict a suitable mixing and compaction temperature based on experience. The objective of this paper is to investigate existing alternative methods which can be suitable for estimating the mixing and compaction temperatures of both warm mix asphalt (WMA) and polymer modified bitumen (PMB) mixtures. For this purpose, several proposed methods have been evaluated named as High Shear Rate method (HSR), Zero Shear Viscosity method (ZSV), and Steady Shear Flow method (SSF). The asphalt mixture mechanical properties such as Marshall Mix design and Indirect Tensile Strength test (ITS) were also measured based on the determined mixing and compaction temperatures through different methods.

The Influence of UV Light on Rheological Properties of Collagen Extracted from Silver Carp Skin.

Acid soluble collagen (ASC) was extracted from Silver Carp fish skin. Collagen was dissolved in acetic acid at varying concentrations and its rheological properties were studied. Steady shear flow properties of collagen solutions at concentrations of 5 and 10 mg/mL were characterized using rheometry at 20 °C. Collagen solutions were irradiated with UV light (wavelength 254 nm) for up to 2 h and rheological properties were measured. All the collagen solutions showed a shear-thinning flow behavior. A constant viscosity region was observed after 1 h of UV irradiation, which showed that collagen molecules were fully denatured. A short treatment with collagen solution by UV (ultraviolet) light led to an increase in viscosity; however, the denaturation temperature of UV-irradiated collagen decreased. Depending on the time of UV treatment, collagen extracted from Silver Carp fish skin may undergo physical crosslinking or photodegradation. Physically crosslinked collagen may find applications in functional food, cosmetic, biomedical, and pharmaceutical industries.