Literatura científica selecionada sobre o tema "Universal viscosity curve"

We have introduced for the first time, a non-viscosity dependent universal calibration curve (UCC) for the successful prediction of the weight-average molecular weights of globular proteins in the range of 8.5–66.2 kDa with no dependence on the solvent viscosity.

Nearly, all dense suspensions undergo dramatic and abrupt thickening transitions in their flow behavior when sheared at high stresses. Such transitions occur when the dominant interactions between the suspended particles shift from hydrodynamic to frictional. Here, we interpret abrupt shear thickening as a precursor to a rigidity transition and give a complete theory of the viscosity in terms of a universal crossover scaling function from the frictionless jamming point to a rigidity transition associated with friction, anisotropy, and shear. Strikingly, we find experimentally that for two different systems—cornstarch in glycerol and silica spheres in glycerol—the viscosity can be collapsed onto a single universal curve over a wide range of stresses and volume fractions. The collapse reveals two separate scaling regimes due to a crossover between frictionless isotropic jamming and frictional shear jamming, with different critical exponents. The material-specific behavior due to the microscale particle interactions is incorporated into a scaling variable governing the proximity to shear jamming, that depends on both stress and volume fraction. This reformulation opens the door to importing the vast theoretical machinery developed to understand equilibrium critical phenomena to elucidate fundamental physical aspects of the shear thickening transition.

The equation σ=Kέm, where σ is the applied stress, έ is the strain rate, K and m are material constants that depend on stress / strain rate, temperature and grain size is often used to describe structural superplasticity. The general shape of the logσ-logέ curve is sigmoidal. Based on limited data, it was suggested by us earlier that a universal σ-έ curve could exist in a properly normalized space. έ and m are normalized with respect to έopt and mmax, the strain rate at which m is a maximum and the maximum m value respectively. Here a multi-dimensional relationship involving σ/σopt-έ/έopt-m/mmax-ΔF0/kT-η/ηopt is developed; σopt corresponds to έopt, ΔF0 is the free energy of activation for the rate controlling mechanism, k the Boltzmann constant, T the absolute test temperature, η the (apparent) viscosity of the superplastic alloy and ηopt is the viscosity of the same alloy for m=1 in a dimensionless σ-έ space. Using data concerning many systems, the phenomenology of structural superplasticity in all classes of materials is shown to be unique.

Rheological and magnetorheological behaviour of monolayer and double layer sterically stabilized magnetic fluids, with transformer oil (UTR), diloctilsebacate (DOS), heptanol (Hept), pentanol (Pent) and water (W) as carrier liquids, were investigated. The data for volumic concentration dependence of dynamic viscosity of high colloidal stability UTR, DOS, Hept and Pent samples are particularly well fitted by the formulas given by Vand (1948) and Chow (1994). The Chow type dependence proved its universal character as the viscosity data for dilution series of various magnetic fluids are well fitted by the same curve, regardless the nonpolar or polar charcater of the sample. The magnetorheological effect measured for low and medium concentration water based magnetic fluids is much higher, due to agglomerate formation process, than the corresponding values obtained for the well stabilized UTR, DOS, Hept and Pent samples, even at very high volumic fraction of magnetic nanoparticles.

Wall-pressure fluctuations can be represented by a spectrum level that is a function of flow-direction wavenumber and frequnecy, Φ (k1, ω). In the theory developed herein the frequency is replaced by a phase speed; ω = ck1. At low wavenumbers the spectrum is a universal function if nondimensionalized by the friction velocity u* and the boundary layer thickness δ, while at high wavenumbers another universal function holds if nondimensionalized by u* and viscosity ν. The theory predicts that at moderate wavenumbers the spectrum must be of the form Φ+ (k+1, ω+ = c+ k+1) = k+1 − 2 P+ (Δc+) where P+ (Δc+) is a universal function. Here Δc+ is the difference between the phase speed and the speed for which the maximum of Φ+ occurs. Similar laws exist in outer variables. New measurements of the wall-pressure are given for a large Reynolds number range; 45,000 < Re = Uoδ/ν < 113,000. The scaling laws described above were tested with the experimental results and found to be valid. An experimentally determined curve for P+ (Δc+) is given.

Wormlike surfactant micelles are widely used in various applications including fracturing technology in oil industry, template synthesis of different nanoobjects, micellar copolymerization of hydrophilic and hydrophobic monomers, and so forth. Most of those applications suggest the solubilization of different additives in the micelles. The present paper is aimed at the comparative study of the effect of the solubilization of hydrophobic (n-decane and 1-phenylhexane) and hydrophilic (N-isopropylacrylamide and acrylamide) substances on the rheological properties and structure of the micelles using several complementary techniques including rheometry, small angle neutron scattering, dynamic light scattering, and diffusion ordered NMR spectroscopy. For these studies, mixed micelles of potassium oleate and n-octyltrimethylammonium bromide containing the excess of either anionic or cationic surfactants were used. It was shown that hydrophobic additives are completely solubilized inside the micelles being localized deep in the core (n-decane, 1-phenylhexane) or near the core/corona interface (1-phenylhexane). At the same time, only a small fraction of hydrophilic additives (14% of N-isopropylacrylamide and 4% of acrylamide) penetrate the micelles being localized at the corona area. Despite different localization of the additives inside the micelles, all of them induce the breaking of wormlike micelles with the formation of either ellipsoidal microemulsion droplets (in the case of hydrophobic additives) or ellipsoidal surfactant micelles (in the case of hydrophilic additives). The breaking of micelles results in the drop of viscosity of the solution up to water value. The main result of this paper consists in the observation of the fact that for all the additives under study, the dependences of the viscosity on the volume fraction of additive lie on the same master curve being shifted along the volume fraction axis by a certain factor depending on the hydrophobicity of the added species. Those data are quite useful for various applications of wormlike surfactant micelles suggesting the solubilization of different additives inside them.

Abstract Rubber friction differs from that of hard solid materials in that it is not linearly related to the normal load and it depends strongly on sliding speed and temperature. There exists an interrelation between these two variables on their effect on the friction coefficient, first observed for the viscosity of liquids and generally described by the universal WLF transformation equation. The friction coefficient at a constant load is then described by a so-called master curve. Such master curves have been obtained on different types of surface and for gum rubbers as well as filled rubbers on wet and dry surfaces and it is shown that they may also be obtained on ice. The shape of the curve and position on the log(aTv) axis depends on the polymer and the track surface structure indicating that two distinct processes determine the friction: adhesion friction akin to a molecular relaxation process and a deformation process in which energy is lost due to the cyclic deformation of the rubber by the surface asperity. To obtain such a master curve it is necessary to keep the experimental speeds so low that the temperature rise in the contact area can be neglected. In practical tire tests, sliding speeds are high and hence the temperature rises with speed. Since the WLF equation is a negative function of temperature, the range of log(aTv) is limited. If thermocouples are used as sliders on rubber, it is shown that the experimental curves as function of speed can be transformed into a part of a master curve. For compound development friction tests, a limited range of track temperatures and speeds are sufficient to ensure a high correlation with road test data. A single point laboratory measurement may correlate with road tests if carefully chosen. More usually, it leads to misleading conclusions. Side force measurements at a reasonably large slip angle also reflect the friction coefficient and are a useful laboratory tool to evaluate the traction properties of tread compounds.

In this study, the rheological behavior of maize kernel was systematically investigated using a dynamic mechanical analyzer. The loss in toughness caused by drying resulted in a downward shift in the relaxation curve and an upward shift in the creep curve. The long relaxation behavior became obvious when the temperature was above 45 °C, resulting from the weakening of hydrogen bonds with temperature. The maize kernel relaxed more rapidly at high temperatures, caused by a reduction in the cell wall viscosity and polysaccharide tangles. The Deborah numbers were all much smaller than one, suggesting that the Maxwell elements showed viscous behavior. Maize kernel, as a viscoelastic material, showed a dominant viscous property at high temperatures. The decline in β with increasing drying temperature indicated an increase in the width of the relaxation spectrum. A Hookean spring elastic portion made up the majority of the maize kernel creep strain. The order–disorder transformation zone of maize kernel was about 50–60 °C. Due to the complexity of maize kernel, the William–Landel–Ferry constants differed from the universal values; these constants should be ascertained through experiments. Time-temperature superposition was successfully used to describe the rheological behavior. The results show that maize kernel is a thermorheologically simple material. The data acquired in this study can be used for maize processing and storage.

The aging and shear rejuvenation behavior of a commercial printing ink have been studied experimentally using creep and oscillation modes. We observed that the printing ink has typical rheological characteristics: time-dependent, reversible and shear-thinning viscosity. Meanwhile, these properties are very strongly influenced by shear history, thus employing pre-shearing to obtain a standard test state is of vital importance. After pre-shearing, the quiescent ink undergoes structural evolution, i.e., aging, including a sol-gel (liquid-solid) transition on the early stage at room temperatures, the higher the temperature, the earlier the sol-gel transition occurs. The degree of aging and shear rejuvenation can be characterized by the waiting time after pre-shearing and the stress dependence of the power-law index. Finally, we use a time-stress superposition to obtain a universal master curve which is able to describe the aging behaviors of the printing ink. This study shows that the aging processes of printing ink for different waiting times are self similar, variation of waiting time just change the time scale and elastic modulus.

The article shows the types of complications that occur mainly in the fields of the Absheron archipelago in Azerbaijan and in the oil fields of the Azerbaijani sector of the Caspian Sea; the most common and frequent of them are the watering of the production of sucker rod pumping wells and the intensity of sand manifestations. It is noted that methods that prevent complications or reduce their negative impact are more appropriate than methods for their elimination. It is proposed to isolate formation water in flooded sucker-rod pumping oil wells using a universal hydrodynamic method; In this method, a liquid barrier should be created in front of the water in the formation, and not a solid barrier, and high-viscosity dead (non-gaseous) oil should be taken as a separating fluid, the specific gravity of which should be equal to the specific gravity of the formation water. The article uses the following five functions of multifunctional measures when carrying out various well survey methods: I. Pouring clean fluid into the annulus to increase the amount of fluid in the wellbore and reduce the concentration of sand particles in it. II. Without stopping the operation of the pumping unit, adding clean oil to the annulus with the help of a unit, raise its static level several meters higher. III. Determination of values of Pk, Po and G in rod deep well pumping wells producing viscous-plastic oil without stopping the operation of the pumping unit. IV. To determine the reservoir pressure in the simplest way, all well production is drained with a hose into the annulus. V. When removing the first lower curve by the method of two-sided restoration of curves without stopping the operation of the pumping unit VI. When applying the extraction method without changing the indicator diagrams S and n of water-cut oil wells. Thus, the use of multifunctional measures improves the performance of the considered wells and provides great economic benefits. Keywords: polyfunctional measure, irrigated well, sand manifestation, corrosion, erosion, wear, complication, pipe space, sand concentration in liquid, recovery curve.

La connaissance des propriétés physico-chimiques des solutions de polymères utilisées en récupération assistée des hydrocarbures (RAH) est essentielle pour une bonne efficience du procédé. Ces travaux avaient pour but de conforter et enrichir un modèle de viscosité universelle dépendant du paramètre de recouvrement C[η] qui permet de prendre en compte l'occupation du milieu par les chaînes macromoléculaires (concentration d'enchevêtrement critique, C*, régimes dilué et semi-dilué). Les effets des microstructures, de la taille et de la composition des polymères ont été étudiés via la synthèse d'une librairie d'échantillons par polymérisation radicalaire contrôlée (RADT/MADIX) : polyacrylamides, copolymères statistiques et asymétriques acrylamide-acrylate de sodium, polyacrylamides post-hydrolysés. Chaque polymère a été caractérisé par chromatographie d'exclusion stérique et par rhéologie capillaire dont les protocoles et techniques ont été optimisées. Les effets de la microstructure sur les propriétés physico-chimiques dimensionnelles, rhéologiques et complexantes ont été déterminés. Mes travaux de thèse doivent répondre aux deux questions principales suivantes : Quel est l'effet de la microstructure et de la dispersité du polymère sur le modèle ? Quelle(s) est (sont) la(les) limite(s) du modèle en termes d'application ? Mes travaux incluent donc l'élaboration de polymères modèles couvrant une large gamme de masses molaires (de quelques dizaines de milliers à plusieurs millions de g/mol). Les polymères modèles sont de structures variées allant d'homopolymères aux copolymères statistiques et à blocs. Après leur caractérisation complète (composition chimique et structure), les propriétés rhéologiques des solutions sont étudiées. Pour cela, mes travaux comprennent le développement, au sein du laboratoire et spécifiquement pour cette étude, d'un rhéomètre capillaire. Les résultats expérimentaux sont alors comparés au modèle établi pour les polymères industriels pour accroître le potentiel du modèle
The knowledge of the physico-chemical properties of polymer solutions for enhanced oil recovery (EOR) is crucial to optimize the process. The purpose of this work was to consolidate and complete an universal viscosity model depending on C[η] parameter. The later allows taking into account the degree of interpenetration of polymer chains (critical concentration, C*, diluted and semi-diluted solutions). Various polymer parameters have been studied as the effects of microstructures, polymer size (molar mass and dispersity) as well as chemical composition. A library of polymer models was elaborated by controlled radical polymerization (RADT/MADIX). Series of polyacrylamides, statistical and asymmetric copolymers of acrylamide-sodium acrylate and post-hydrolyzed polyacrylamides were synthesized and characterized by steric exclusion chromatography and capillary rheology and the analytical protocols and techniques were optimized. The effects of the microstructure onto dimensional, rheological and complexation physico-chemical properties were determined