Viscosity Of Solids Research Articles

General theory of the viscosity of liquids and solids from nonaffine particle motions.

A microscopic formula for the viscosity of liquids and solids is derived rigorously from a first-principles (microscopically reversible) Hamiltonian for particle-bath atomistic motion. The derivation is done within the framework of nonaffine linear response theory. This formula may lead to a valid alternative to the Green-Kubo approach to describe the viscosity of condensed matter systems from molecular simulations without having to fit long-time tails. Furthermore, it provides a direct link between the viscosity, the vibrational density of states of the system, and the zero-frequency limit of the memory kernel. Finally, it provides a microscopic solution to Maxwell's interpolation problem of viscoelasticity by naturally recovering Newton's law of viscous flow and Hooke's law of elastic solids in two opposite limits.

Characterization of magnesium oxide nanoparticle for water-based drilling mud formulation

This research is based on the synthesis and analysis to determine the efficiency and cost effectiveness of nanoparticle materials used in drilling fluid during oilfield exploration process. The study was carried out in the formulation of a waterbased drilling fluid, in which the prepared additives were treated with magnesium oxide (MgO) nanoparticles. The rheological properties of nanoparticle materials, such as flow time, viscosity, shear rate, shear stress, torque difference, and separation of solids and liquids, have been determined. The study also analyzed the fluid loss with respect to time in a manual filter press for low temperature and low pressure versus high pressure and high temperature using filter press hydraulic dead weight assembly in high temperature and high pressure. The nanoparticle used for the study was characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffractometer and particle size analyzer. Viscosity parameters were optimized using a multi-speed viscometer, lubricity tester and pH meter at effective concentration, as well as contact time, temperature and pressure changes as a function of concentration. The study suggests the use of MgO nanoparticle as an additive for water-based mud exploration in oilfields.

On Nanosecond Thermophysics (Review)

A review of highly nonequilibrium states generated in solids and liquids by a short shock-wave action is presented. States with large deviator stress components, large negative pressures, overheating of the solid phase, supercooling of the liquid phase, and issues of viscosity of liquids (including metal melts) and solids at strain rates up to 108 s–1 and high pressures are considered. The dynamic tensile strength (cavitational strength) of metal melts, fast polymorphic transformations, and a new rule for selecting the detonation velocity of explosives are discussed.

Predicting the Viscosity of Petroleum Emulsions Using Gene Expression Programming (GEP) and Response Surface Methodology (RSM)

This paper summarizes an investigation of certain operating parameters on the viscosity of petroleum emulsions. The production of crude oil is accompanied by emulsified water production, which comes along with various challenges like corroding the transport systems and catalysts poisoning during petroleum refining in the downstream. Several process variables are believed to affect the ease with which emulsified water can be separated from emulsions. Some of the issues have not been extensively examined in the literature. The simplicity with which water is separated from petroleum changes with age (after formation) of the emulsion; notwithstanding, this subject has not been investigated broadly in literature. This study tries to assess the correlation between aging time, water cut, crude oil viscosity, water viscosity and amount of solids and viscosity of petroleum emulsions. To achieve that, a response surface methodology (RSM) based on Box-Behnken design (BBD) was used to design the experiment. Synthetic emulsions were prepared from an Offshore Malaysian Crude oil based on the DoE design and were aged for 7 days. The emulsions viscosities were measured at 60-degree Celsius using an electromagnetic viscometer (EV100). The broad pressure and temperature range of the HPHT viscometer permit the imitation of acute conditions under which such emulsions may form. The data obtained from the RSM analysis was used to develop a prediction model using gene expression programming (GEP). It was discovered that the viscosity of water has no effect on the viscosities of the studied emulsions, as does the water cut and amount of solids. The most significant factor that affects emulsion viscosity is the aging time, with the emulsion becoming more viscous over time. This is believed to be imminent because of variations in the interfacial film structure. This is followed by the amount of solids, also believed to be as a result of increasing coverage at the interface of the water droplets, limiting the movements of the dispersed droplets (reduced coalescence), thereby increasing the viscosity of the emulsions.

Rheological properties for fresh cement paste from colloidal suspension to the three-element Kelvin–Voigt model

In the present work, rheological behaviors of fresh cement paste are studied based on multi-disciplinary approaches, i.e., colloidal suspension using attractive van der Waals force, rheology using the Bingham model and Bingham–Papanastasiou model, which are able to describe the behavior of cement pastes before and after yield stress, and finally the continuum mechanics based on Maxwell and Kelvin–Voigt models. To achieve this, the fresh cement paste with different water-to-cement ratios of 0.3 up to 0.6 is prepared. The attractive van der Waals forces are estimated based on the distances between solid cement particles, which vary at every single water-to-cement ratio. The rheology experiments of all water-to-cement ratios are performed using a rheometer. According to our experimental outcomes, the Bingham and Bingham–Papanastasiou models are applied in the modeling of the experimental curves and determination of yield stress and viscosity. Maxwell and the Kelvin–Voigt models are utilized in describing solid-like behavior before yield stress and fluid-like behavior beyond yield stress. It is observed that the increase of water generates a decrease in the viscosity, yield stress, and packing concentration of solids. It also increases the distances between two cement particles in the cement pastes. According to the modeling results, the Bingham–Papanastasiou model is well adapted for the cement paste flow due to its additional modeling parameter, which is known as m. The role of m is understood and described by linking the van der Waals interaction, rheology, and three-element Kelvin–Voigt model as a whole in function of water-to-cement ratio. m is understood as a key parameter in which the distance between particles affects the rheological behavior of fresh cement pastes. Lastly, the two-phase flow simulations have been successfully achieved and compared with the experiments. The conclusion and outlooks are summarized and discussed at the end of the paper.

Predicting the viscosity of solids using steady-state creep behavior of the fibrous composites semi-theoretically

A semi-analytical formulation is presented for obtaining the viscosity of solids (such as metals) using the steady state creep model of the short-fiber composites. For achieving this aim, fluid mechanics theory is used for determining the viscosity. Sometimes, obtaining the viscosity is experimentally difficult and intricate. So, the present model may be beneficial to obtain the viscosity of metals.

Novel Functional Whey-Based Drinks with Great Potential in the Dairy Industry.

This work focuses on the production of liquid whey protein concentrates by ultrafiltration followed by thermal denaturation and homogenization of the ultrafiltrated concentrate, as well as on the production of ultrafiltrated permeates concentrated by reverse osmosis. Kefir grains (fresh and thawed) and/or commercial probiotic bacteria were inoculated in both liquid whey protein concentrates and concentrated ultrafiltrated permeates and grown at 25 °C for 24 h for the manufacture of fermented drinks. The physicochemical characterization (pH, titratable acidity, viscosity, and content of total solids, ash, fat and proteins) of the obtained drinks was then assessed and compared. Enumeration of viable microorganisms was carried out immediately after inoculation (at 0 h), during the fermentation period (at 12 and 24 h) and during refrigerated storage (at 48, 168 and 336 h). The fermented drinks showed acceptable physicochemical and sensorial properties, and contained above 7 log CFU/mL of lactococci and lactobacilli and 6 log CFU/mL of yeasts after 14 days of refrigerated storage, which is in agreement with the standards required by international organizations like European Food Safety Authority (EFSA) and Food and Drug Administration (FDA) for products containing probiotics. In summary, the strategy developed in this work contributes to the expansion of the applications of products derived from whey fractionation for the design of novel functional foods.

Pressure dependence of glass transition in As2Te3 glass.

Amorphous solids prepared from their melt state exhibit glass transition phenomenon upon heating. Viscosity, specific heat, and thermal expansion coefficient of the amorphous solids show rapid changes at the glass transition temperature (Tg). Generally, application of high pressure increases the Tg and this increase (a positive dT(g)/dP) has been understood adequately with free volume and entropy models which are purely thermodynamic in origin. In this study, the electrical resistivity of semiconducting As(2)Te(3) glass at high pressures as a function of temperature has been measured in a Bridgman anvil apparatus. Electrical resistivity showed a pronounced change at Tg. The Tg estimated from the slope change in the resistivity-temperature plot shows a decreasing trend (negative dT(g)/dP). The dT(g)/dP was found to be -2.36 °C/kbar for a linear fit and -2.99 °C/kbar for a polynomial fit in the pressure range 1 bar to 9 kbar. Chalcogenide glasses like Se, As(2)Se(3), and As(30)Se(30)Te(40) show a positive dT(g)/dP which is very well understood in terms of the thermodynamic models. The negative dT(g)/dP (which is generally uncommon in liquids) observed for As(2)Te(3) glass is against the predictions of the thermodynamic models. The Adam-Gibbs model of viscosity suggests a direct relationship between the isothermal pressure derivative of viscosity and the relaxational expansion coefficient. When the sign of the thermal expansion coefficient is negative, dT(g)/dP = Δk/Δα will be less than zero, which can result in a negative dT(g)/dP. In general, chalcogenides rich in tellurium show a negative thermal expansion coefficient (NTE) in the supercooled and stable liquid states. Hence, the negative dT(g)/dP observed in this study can be understood on the basis of the Adams-Gibbs model. An electronic model proposed by deNeufville and Rockstad finds a linear relation between Tg and the optical band gap (Eg) for covalent semiconducting glasses when they are grouped according to their average coordination number. The electrical band gap (ΔE) of As(2)Te(3) glass decreases with pressure. The optical and electrical band gaps are related as Eg = 2ΔE; thus, a negative dT(g)/dP is expected when As(2)Te(3) glass is subjected to high pressures. In this sense, As(2)Te(3) is a unique glass where its variation of Tg with pressure can be understood by both electronic and thermodynamic models.

Post‐stroke dysphagia: progress at last

Oropharyngeal Dysphagia (OD) is both underestimated and underdiagnosed as a cause of malnutrition and respiratory complications following stroke. OD occurs in more than 50% of stroke patients. Aspiration pneumonia (AP) occurs in up to 20% of acute stroke patients and is a major cause of mortality after discharge. Systematic screening for OD should be performed on every patient with stroke before starting oral feeding, followed, if appropriate by clinical and instrumental (videofluroscopy and/or fiberoptic endoscopy) assessment. Bolus modification with adaptation of texture and viscosity of solids and fluids and postural adjustments should be part of the minimal treatment protocol, but they do not change the impaired swallow physiology nor promote recovery of damaged neural swallow networks in stroke patients. To this purpose, two new neurostimulation approaches are being developed to stimulate cortical neuroplasticity to recover swallowing function: (i) those aimed at stimulating the peripheral oropharyngeal sensory system by chemical, physical or electrical stimulus; and (ii) those aimed at directly stimulating the pharyngeal motor cortex, such as repetitive transcranial magnetic stimulation (rTMS). The study of Park et al. in this issue of Neurogastroenterology and Motility evaluated the effect of rTMS in dysphagic stroke patients and showed a marked improvement in swallow physiology. Other studies also using rTMS showed plastic changes in pharyngeal motor cortical areas relevant to swallowing function. If further randomized controlled trials confirm these initial results, the neurorehabilitation strategies will be introduced to clinical practice sooner rather than later, improving the recovery of dysphagic stroke patients. Progress at last.

Influence of Boundary Conditions on CFD Simulation of Gas- particle Hydrodynamics in a Conical Fluidized Bed Unit

The hydrodynamics of gas-particle conical fluidized bed containing dried TiO2 micro-size particles were studied experimentally and computationally. The pressure drop was studied by pressure measurements and mean solid velocity in the different axial and radial positions and their experimental values were measured by a parallel 3-fiber optical probe. The Eulerian-Eulerian multiphase model, including kinetic theory of granular flow using Gidaspow (1994) drag function was used in the computational fluid dynamics (CFD) simulation. The frictional viscosity of solids is predicted from the equation proposed by Schaeffer (1987), whereas semi-empirical boundary equations developed by Johnson and Jackson (1987) were applied for the tangential velocity and granular temperature of the solids at the wall. Three different types of boundary conditions (BC), consisting in free-slip/no-friction, no-slip/friction and high-slip/small-friction, were used in this work to compare the results of the model with the experimental data. The numerical predictions using free-slip/no-friction BC agreed reasonably well with the experimental pressure drop measurements, especially at superficial gas velocities higher than the minimum fluidization velocity, Umf. The results for simulated mean axial solid velocity show that the free-slip BC was in better agreement with the experimental data compared with the other boundary conditions. The model also provides reasonable predictions for particle circulation and formation of fountain zone, gulf-effect and air velocity.

Modeling of viscosity for power plant ash slurry at higher concentrations: Effect of solids volume fraction, particle size and hydrodynamic interactions

The rheological behaviour of five fly ash samples (having different d 50) collected from a thermal power plant has been investigated over a range of volumetric solids concentration ( ϕ = 0.32–0.4945) in shear rate range of 10–200 s − 1 . The slurry was highly pseudo-plastic whose behavior can be described by a non-Newtonian power law model in the range of solids concentration studied. The maximum solids fraction ( ϕ m ) at which the slurry viscosity approaches infinity, was determined for the fly ash samples using the relationship between inverse of relative viscosity (i.e. 1 μ r ) and volume fraction of solids ϕ. A model incorporating maximum solids fraction ( ϕ m ), power law index ( n), median particle size ( d 50), co-efficient of uniformity ( C U), shear rate ( γ̇) has been developed to predict the viscosity. The model predictions and the experimental data matched quite well for all five samples and it is expected to be quite helpful in evaluating the hydraulic parameters for design of commercial high concentration fly ash slurry pipelines. The most important variables such as volume fraction of solids, particle size, and size distribution, and their effect on the hydrodynamic forces in a non-Newtonian laminar flow regime are discussed.

Intrinsic Viscosity of Proteins and Platonic Solids by Boundary Element Methods.

The boundary element (BE) method is used to implement a very precise computation of the intrinsic viscosity for rigid molecules of arbitrary shape. The formulation, included in our program BEST, is tested against the analytical Simha formula for ellipsoids of revolution, and the results are essentially numerically exact. Previously unavailable, very precise results for a series of Platonic solids are also presented. The formulation includes the optional determination of the center of viscosity; however, for globular proteins, the difference compared to the computation based on the centroid is insignificant. The main application is to a series of 30 proteins ranging in molecular weight from 12 to 465 kD. The computation starts from the crystal structure as obtained from the Protein Data Bank, and a hydration thickness of 1.1 Å obtained in previous work with BEST was used. The results (extrapolated to an infinite number of triangular boundary elements) for the proteins are separated into two groups: monomeric and multimeric proteins. The agreement with experimental measurements of the intrinsic viscosity in the case of monomeric proteins is excellent and within experimental error of 5%, demonstrating that the solution and crystal structure are hydrodynamically equivalent. However, for some multimeric proteins, we observe strong systematic deviations around -20%, which we interpret as a systematic deviation of the solution structure from the crystal structure. A possible description of the structural change is deduced by using simple ellipsoid model parameters. A method to obtain intrinsic viscosity values for proteins to 1-2% accuracy (better than experimental error) on the basis of a single BE computation (avoiding the need for an extrapolation on the number of surface triangles) is also presented.

Structural Viscosity of Solids

Simple estimates of the coefficient of dynamic viscosity of some metals are considered. Experimental results on shock loading of aluminum, copper, and steel plane specimens are given. It is shown that the coefficient of dynamic viscosity depends on the characteristic size of the structural level of plastic strain at which loading-energy dissipation is considered. It was found that the main level that determines the viscosity of materials under high-velocity loading is the mesoscopic level with a characteristic size of ≈ 10 μm. Key words: viscosity, high-velocity loading, mesoscopic level, interferogram.

Anomalous absorption of bulk shear acoustic waves by an ultra-thin layer of a non-Newtonian fluid

A strong maximum of absorptivity (as much as dozens of per cent) of bulk shear acoustic waves by an ultra-thin layer of a non-Newtonian fluid between two solid surfaces is shown to be achieved at an optimal layer thickness. This optimal thickness is demonstrated to be usually much smaller than the wavelength and the wave penetration depth in the fluid. The coefficients of reflection, transmission, and absorption of shear waves polarized perpendicular to the plane of incidence are determined as functions of incidence angle, layer thickness, fluid viscosity, relaxation time(s), frequency, and parameters of solids. A frictional contact approximation, in which the layer can be considered as a contact with friction is justified for non-Newtonian fluids. The anomalous absorption of bulk shear waves in thin nonuniform fluid layers with viscosity and/or relaxation time varying across the layer is analyzed in the frictional contact approximation. It is shown that unlike the anomalous absorption in Newtonian fluids, the anomalous absorption in non-Newtonian fluid layers is frequency dependent even in the frictional contact approximation. This dependence is analyzed analytically and numerically.

An experimental study on the shear viscosity of solids

Viscoelastic solids with high viscosity were experimentally studied with the intention of having them deformed under uniform shear stress. A kind of sandwich method was developed for applying a constant shear stress to a specimen, and its deformation was observed optically using heterodyne interferometry with a sensitivity of 10 nm in displacement measurement. Time-dependent deformation data were analyzed on the basis of a mechanical model of anelasticity plus viscosity. Viscosity in the range of 108–1014 Pa⋅s could be determined at temperatures of 20–200 °C. Through a simulation using the finite element method together with an experiment visualizing the deformation, the specimen deformation was shown to be of an almost uniform shear mode. Experiments were performed to determine the temperature dependence of viscosity for several kinds of glasses near their glass transition Tg, and the determined viscosity values were about 107 Pa⋅s at Tg. The viscosity values measured by a rotation disk viscometer were in good agreement with the present data. The viscosity of some glasses was also measured by the beam bending and penetration methods, and values of 109–1012 Pa⋅s at Tg were obtained. The large discrepancy between the two kinds of data was considered.

A new apparatus for measuring high viscosity of solids

A new apparatus which is capable of measuring Newtonian viscosity as high as 108-1014 Pa · s has been developed. The upper and the lower faces of a cubic specimen 1 x 1 x I cm3 in size are respectively bonded to movable and fixed plates, and a constant shear stress is applied to the specimen. The displacement of the upper plate is measured and recorded as a function of time utilizing the HP-5528A optical laser measuring system. The sensitivity of the displacement measurement is 10 nm. Measurements at temperatures up to 200°C can be made by using a small furnace installed around the specimen. A variety of adhesive materials, polymers and ceramics, have been tested for the specimen-plate bonding. Aqueous Sauereisen cement showed a stable and rigid bonding in the experimental temperature range. Experiments for rubber (soft) and silicon crystal (hard) specimens have been performed to ascertain the reliability of the present method. The apparatus is also able to measure the anelasticity (mechanical relaxation) of solids, but is not adaptable to the measurement of the shear modulus of specimens; because the instantaneous displacement of the movable plate at the moment of the loading is mostly due to the rotational and inhomogeneous elastic deformations of the specimen.

Friction and energy dissipation at the atomic scale: A review

Discussions of energy dissipation during friction processes have captured the attention of engineers and scientists for over 300 years. Why then do we know so little about either dissipation or friction processes? A simple answer is that we cannot see what is taking place at the interface during sliding. Recently, however, devices such as the atomic force microscope have been used to perform friction measurements, characterize contact conditions, and even describe the ‘‘worn surface.’’ Following these and other experimental developments, friction modeling at the atomic level—particularly molecular dynamics (MD) simulations—has brought scientists a step closer to ‘‘seeing’’ what takes place during sliding contact. With these investigations have come some answers and new questions about the modes and mechanisms of energy dissipation at the sliding interface. This article will review recent theoretical and experimental studies of friction processes at the atomic scale. Theoretical treatments range from simple, analytical models of two-dimensional, coupled ball-spring systems at 0 K, to more complex MD simulations of three-dimensional arrays of hydrogen- and hydrocarbon-terminated surfaces at finite temperatures. Results are presented for the simplest yet most practical cases of sliding contact: sliding without wear. Sliding without friction is seen in weakly interacting systems. Simple models can easily explain the energetics of such friction processes, but MD studies are needed to explore the dynamics (excitation modes, energy pathways,...) of thermally excited atoms interacting in three-dimensional fields. These studies provide the first atomic-scale models for anisotropic friction and boundary lubrication. Friction forces at atomic interfaces must ultimately be measured at the macroscopic level; these measurements, which depend on the mechanical properties of the measuring system, are discussed. Two rather unique experimental studies of friction are also reviewed. The first employs a ‘‘surface force apparatus’’ to measure adhesion and friction between surfactant monolayers. The correlation of adhesion hysteresis and friction provides a new mechanism of friction; moreover, the interpretation for the effect—hysteresis from entanglement of the molecular chains during a phase transformation—implies that the dynamics are taking place at an accessible time scale (seconds to minutes). The second study extends the time domain at which friction can be measured to the nanosecond scale. A quartz-crystal oscillator is used to monitor the viscosity of monolayer liquids and solids against solid surfaces. Interfaces slip angstroms in nanoseconds. Modelers have suggested a variety of mechanisms for this atomic-scale friction process, from defect-mediated sliding to electron drag effects. The article ends by identifying the vast, barely charted time-space domain (micro-to-pico time and length scales) in which experiments are needed to further understand the dynamic aspects of friction processes.

Apparent viscosity of particulate solids determined using creepanalysis

Creep compliance measurements were used to quantify the ability of a range of materials to undergo plasticdeformation. Dibasic calcium phosphate dihydrate, anhydrous lactose, sodium bicarbonate, sodium chloride, partially pregelatinised corn starch and two types of microcrystalline cellulose represented materials with principal consolidation mechanisms ranging from brittle fracture to extensive plastic deformation. As the porosity of a compact decreased, apparent viscosity increased due to increasing resistance to viscous flow. An exponential relation was shown between apparent viscosity and porosity. Test conditions, including the porosity of the sample, should be specified when quoting a value of apparent viscosity derived from such tests.

Cutting resistance of rocks

A theory is suggested for rock cutting resistance based on a model of cutting in a brittle mode, i.e. with a latent internal sliding crack. The theory considers any plastic, viscous and other irreversible strains for a body subjected to cutting;. and also any spatial configuration of the cutter. The maximum cutting force in relation to cutting depth, cutting tool shape, initial stressed state, and rock properties is worked out using the invariant Γ-integral. It is established that the maximum cutting force in a brittle mode is only governed by the sliding viscosity of the rock and it does not depend on its other elastic and strength characteristics. A simpler equation derived by the authors previously emerges in the particular case of a plane-stressed or plane-strained sliding viscosity of solids from the results of experiments with cutting by any cutting tool of spatial configuration. Some results are given for the experiments of cutting typical sedimentary rocks.

Mathematical Model of Viscosity Measurements for Viscoelastic Solids

A methodology is described for determining the viscosity of viscoelastic solids. A three-parameter model consisting of two springs and one dashpot is constructed to represent the viscoelastic material. With this model, the viscosity can be determined from the experimental stress-time curve generated from short-term loading at a constant strain rate, followed by holding the total strain. The feasibility of this model to represent viscoelastic ceramics is also addressed.