Composition Dependence Of Viscosity Research Articles

Temperature and composition dependence of viscosity, refractive index and thermodynamics of viscous flow for benzonitrile + methyl/ethyl/butyl methacrylate binary systems: Experimental and theoretical study

Temperature and composition dependence of viscosity, refractive index and thermodynamics of viscous flow for benzonitrile + methyl/ethyl/butyl methacrylate binary systems: Experimental and theoretical study

Anomalous Concentration Dependence of Viscosity: Hidden Role of Cross-Correlations in Aqueous Electrolyte Solutions.

The viscosity of aqueous electrolyte solutions exhibits well-known composition-dependent anomalies that show certain definitive trends and universal features. The viscosity of LiCl and NaCl solutions increases with concentration in a monotonic fashion, while solutions of KCl, RbCl, and CsCl exhibit a more complex behavior. Here, the viscosity first decreases and then increases with increasing concentration, with a rather broad minimum at intermediate concentrations (ca. 1-3 m). To unearth the origin of such puzzling behavior, we carried out detailed molecular-level analyses by interrogating the exact Green-Kubo expression of viscosity in terms of the stress-stress time correlation function (SS-TCF). The total SS-TCF can be decomposed into a collection of three self- and three cross-SS-TCFs arising from the three constituent components (water, cations, and anions). Mode coupling theory (MCT) analysis for the friction on ions and the viscosity of the solution suggests the possible importance of two-particle static and time-dependent cross-correlations between water and the ions. We calculate the viscosity and other dynamical properties for all five electrolyte (LiCl, NaCl, KCl, RbCl, and CsCl) solutions over a range of concentrations, using two models of water (SPC/E and TIP4P/2005). The total viscosity derives non-negligible contributions from all of the terms. The cross-correlations are found to be surprisingly large and seen to play a hidden role in the concentration dependence. However, the importance of cross-correlations is often not discussed. Our study leads to a theoretical understanding of the microscopic origin of the observed anomalies in the composition dependence of viscosity across all five electrolytes.

Measurement and correlation of density and viscosity of n-alcohol–water mixtures at temperatures up to 618 K and at pressures up to 40 MPa

Densities and viscosities of methanol-water, ethanol-water and n-propanol-water mixtures were measured over the entire range of compositions at temperatures from 523.2 to 618.2 K and at pressures up to 40 MPa. The excess molar volume calculated from the measured density changed negative to positive with increasing alcohol composition at some conditions studied, and this behavior was observed at lower temperature with increasing alkyl chain length. Maxima in composition dependence of viscosity, which is generally observed in ambient conditions, were not present at 618.2 K. Viscosities could be correlated with the Eyring's theory to within 6.4% at temperatures up to 476.2 K. The Peng-Robinson equation of state and Redlich-Kister mixing rule were used to obtain the excess Gibbs energy included in the Eyring's theory, and two binary interaction parameters in the mixing rules were determined by fitting of viscosity data. The densities were predicted using the volume translated Peng-Robinson equation of state to within 3.2% with parameters being determined by viscosity data at temperatures up to 476.2 K. A switching of fitting parameters from binary interaction parameters of the equation of state mixing rule to a proportionality constant, σ, of Eyring's theory was introduced, and viscosities and densities of the normal alcohol-water mixtures could be correlated and predicted to within 4.6% and 8.9%, respectively at temperatures above 476.2 K.

Viscosity and configuration entropy of glasses for CHROMPIC vitrification

The composition and temperature dependence of viscosity and configuration entropy of glasses with chemical composition close to that used for CHROMPIC radioactive waste vitrification were studied. The composition of fifteen studied glasses was derived from the composition of currently used glass frit by increasing/decreasing the content of each particular oxide and retaining the same relative amounts of the other components. The high-temperature viscosity in the range (101.8–103.0) dPa s was measured by the falling ball method while the low-temperature viscosity in the range (108–1012) dPa s was measured by the thermomechanical analysis. The experimental viscosity data were smoothed by the Vogel–Fulcher–Tammann viscosity equation. The temperature–composition dependence of viscosity was described by the Adam and Gibbs viscosity equation. The influence of increasing/decreasing content of particular oxides on the values of parameters of the Adam and Gibbs viscosity equation and on the value of configuration entropy was quantified and discussed.

Viscosity of heavy n-alkanes and diffusion of gases therein based on molecular dynamics simulations and empirical correlations

The viscosity of pure n-alkanes and n-alkane mixtures was studied by molecular dynamics (MD) simulations using the Green–Kubo method. n-Alkane molecules were modeled based on the Transferable Potential for Phase Equilibria (TraPPE) united atom force field. MD simulations at constant number of molecules or particles, volume and temperature (NVT) were performed for n-C8 up to n-C96 at different temperatures as well as for binary and six-component n-alkane mixtures which are considered as prototypes for the hydrocarbon wax produced during the Gas-To-Liquid (GTL) Fischer–Tropsch process. For the pure n-alkanes, good agreement between our simulated viscosities and existing experimental data was observed. In the case of the n-alkane mixtures, the composition dependence of viscosity was examined. The simulated viscosity results were compared with literature empirical correlations. Moreover, a new macroscopic empirical correlation for the calculation of self-diffusion coefficients of hydrogen, carbon monoxide, and water in n-alkanes and mixtures of n-alkanes was developed by combining viscosity and self-diffusion coefficient values in n-alkanes. The correlation was compared with the simulation data and an average absolute deviation (AAD) of 11.3% for pure n-alkanes and 14.3% for n-alkane mixtures was obtained.

Application of Optical Basicity for Estimation of Viscosity of SiO<sub>2</sub>-CaO-MgO-Al<sub>2</sub>O<sub>3</sub> System

A viscosity model based on NPL model with the corrected optical basicity is proposed for quaternary SiO2-CaO-MgO-Al2O3 slag system in the present work. The modified Arrhenius type of equation for temperature dependence of slag viscosity is employed. By means of fitting measured viscosity values for slags with basicity from 0.4 to 1.0 and temperature from 1593 to 1803 K, model parameters are optimized against values of optical basicity, which represents both the structure of molten slags and cationic effects. The relationship between model parameters and optical basicity, which is different from NPL model, is obtained. The present model is applied to estimate viscosity values of slag in SiO2-CaO-MgO-Al2O3 system. The comparison between estimated and measured values shows good agreement with a mean deviation of 12%. It proves fully that the present model can express the temperature dependence and composition dependence of viscosity.

Heat partitioning in terrestrial planets during core formation by negative diapirism

We investigate the gravitational heat partitioning between silicate and metallic phases during core formation by negative diapirism in terrestrial planets. We model the dynamic evolution of an iron diapir, sinking through a solid silicate proto-mantle. Our calculations include viscous heating and strong temperature and composition-dependence of viscosity. We show that the diapir mean temperature evolves towards an asymptotic value T d∞, which depends on the efficiency of viscous heating and heat transfer between the diapir and its surroundings, and on the viscous rheology. We derived a simple analytic model that captures the thermal evolution observed in our numerical experiments. This model can be applied to determine the heat distribution within terrestrial planets with a large number of diapirs, during their growth and early differentiation. We show that the partitioning of core formation heating during negative diapirism depends strongly on the size distribution of the iron diapirs. A large number of small sinking iron diapirs favors metal–silicate heat exchange and leads to a relatively hot core, which allows a sustainable dynamo, as on Earth. A small number of large diapirs have the opposite effect and could correspond to a Mars-like planet with an early dynamo that is no longer active. In all cases, negative diapirism tends to leave the lowermost mantle significantly hotter than its upper part, which could trigger large amounts of melting in the early deep mantle.

Relaxation in binary mixtures: Non-ideality, heterogeneity and re-entrance

Binary mixtures show many kinds of fascinating dynamical behaviour which has eluded microscopic description till very recently. In this work we show that much of the anomalous behaviour can be explained by building suitable models and carrying out theoretical and simulation studies. Specifically, three well-known problems have been addressed here. (a) Non-ideality in composition dependence of viscosity, (b) re-entrant behaviour of orientational relaxation, and (c) heterogeneity in supercooled binary mixtures. The physical origin of the dynamical behaviour of binary mixtures can be understood in terms of composition fluctuation, a study of which has also been presented in this paper.

Temperature and composition dependence of viscosity. II. Temperature dependence of viscosity of propylene carbonate-dimethoxyethane mixtures

The application of the currently used equations for the reproduction of the temperature dependence of viscosity η of binary solvent mixtures of propylene carbonate (PC) and dimethoxyethane (DME) favors the choice of the Vogel-Fulcher-Tammann (VFT) equation using the ideal glass transition point as the reference temperature To for the estimation of free and blocked (inaccessible) volumes. Reduced plots show that the free volumes as obtained from the VFT equation mainly determine the viscosities of the liquid mixtures; the blocked volumes Vx(To)≡Vo (x: mole fraction of PC) show ideal behavior. The effect of negative excess volumes V E on viscosity, studied in the preceding paper, is examined in comparison with the effect of a temperature decrease. The equal signs of η E and V E can be explained by referring the viscosities to the reference temperature To.

Temperature and composition dependence of viscosity I. Propylene carbonate-dimethoxyethane mixtures and thermodynamics of fluid flow

Concentration and temperature dependence of viscosity of propylene carbonate (PC)/dimethoxyethane (DME) mixtures were studied at temperatures between −45 and 25°C. Among various semiempirical ≠(x)-functions available for data analysis, only the McAllister equation fits the data precisely. Thermodynamic quantities obtained from such an analysis results in an interpretation of the structure of this binary system consistent with results from other methods.

Non-linear properties of supercooled liquids in the system Na 2OSiO 2

The physical properties, viscosity, density, heat capacity and thermal expansivity, of relaxed supercooled liquids in the temperature range just above the glass transition have been determined for ten compositions along the compositional binary Na 2OSiO 2, in the range of 2–45 mole% Na 2O, by a combination of scanning calorimetry, dilatometry and micropenetration viscometry. The viscosity, density, heat capacity and thermal expansivity in the glassy state have also been determined. The heat capacities illustrate a linear composition dependence for the glassy state and a smooth but strongly non-linear composition dependence for the supercooled liquid state. The thermal expansivities were determined by dilatometry up to the glass transition and, by a normalized comparison of relaxation behavior in the glass transition interval, to temperatures ∼50°C above the glass transition. The expansivity is a linear function of the molar composition in the glass but a strongly non-linear function of molar composition in the supercooled liquid. The viscosity data just above the glass transition temperature, combined with data from high temperature using the concentric cylinder method, illustrate that the composition dependence of viscosity is strongly non-linear and exhibits an inflection as a function of composition. The glass transition temperature, taken as the peak temperature of the calorimetric measurements, is not in general an isokom in this system. The data for these property determinations in the Na 2OSiO 2 system provide much improved constraints on the partial molar properties of SiO 2 liquid and partial molar properties of the SiO 2 component in silicate melts. The complex behavior of the transport properties, i.e. the glass transition temperature and the viscosity, point to complexities in viscous flow beyond that of simple binary mixing of the Na 2O and SiO 2 components.