The inflection point in the pressure dependence of viscosity under high pressure: a comprehensive study of the temperature and pressure dependence of the viscosity of propylene carbonate

The pressure dependence of the prototypical glass-former propylene carbonate has been investigated over a broad range of temperature and pressure that were inaccessible in previous investigations using dielectric spectroscopy. We find that the viscosity measurements validate the scaling relation, eta(T,V)=J(TV gamma), with a scaling parameter gamma close to that found from dielectric relaxation measurements. In the pressure dependence of the viscosity, we observe an inflection point in the log eta versus P response, similar to that found previously for other materials. However, this inflection has never been observed in dielectric relaxation measurements. Using the scaling property above, it is possible to determine the behavior of the dielectric relaxation time in this otherwise inaccessible experimental range and compare it with the viscosity measurements. We find that the behaviors of eta and tau are very similar, and a very good agreement between the function phi P calculated for these two quantities is found. Starting from the validity of the scaling properties, we show that the inflection point in the pressure dependence of the viscosity can be attributed to the convolution of the pressure dependences of the compressibility kappa T and the apparent activation energy at constant volume EV.     

Temperature dependence of the dynamic viscosity of liquid mercury

The dependence of the dynamic viscosity of mercury on temperature is calculated and expressed in terms of the cluster associate model, based on the Boltzmann distribution and with normalization at the melting point. The resulting refined equation for mercury viscosity adequately reflects this dependence over the range of the liquid state, including the critical point.     

Scaling analysis of the temperature dependence of intrinsic viscosity

The scaling predictions for the temperature dependence of the intrinsic viscosity of flexible polymers are briefly reviewed. When the predictions are fit to a power law over a fixed range of chain length, a relation between the exponent and prefactor of the Mark–Houwink–Sakurada equation emerges. In comparing with the experimental data compilation of Rai and Rosen, we conclude that real polymer systems are nowhere near the true good solvent limit, even when the exponent matches the good solvent prediction. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1989–1991, 1997     

The pressure and temperature dependence of methane decomposition

Single-channel hindered Gorin model RRKM calculations were performed on reaction (1). (1) Good agreement between theory and experiment was obtained for the temperature and pressure dependence of reaction (1). Isotopic data for the reverse association reaction, (?1), reported previously, are consistent with the model. Rate constants were cast in the form of an analytical expression and appropriate parameters were tabulated.     

On the viscosity of two 1-butyl-1-methylpyrrolidinium ionic liquids: Effect of the temperature and pressure

A new calibration procedure was used and four new temperature probes have been placed on a falling-body viscometer to improve its accuracy. The new configuration and calibration procedure allow measuring viscosities with an uncertainty of 3.5% at pressures up to 150 MPa. This device was employed to measure viscosities as a function of temperature and pressure for two ionic liquids (ILs): 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate and 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate. Besides, we have measured the flow curves at pressures up to 75 MPa and shear rates up to 1000 s⁻¹ in a Couette rheometer. Dynamic viscosities were correlated as function of temperature and pressure with four different equations with average absolute deviation lower than 1%. The pressure-viscosity and temperature-viscosity derived properties were analyzed and compared with those of other ionic liquids. Furthermore, experimental data were used to check the application of the thermodynamic scaling approach as well as the hard-sphere scheme. Both models represent the viscosity values with average relative deviations lower than 2%.     

Experimental evaluation of the pressure and temperature dependence of ion-induced nucleation

An experimental system for the study of ion-induced nucleation in a SO(2)/H(2)O/N(2) gas mixture was developed, employing a soft x-ray at different pressure and temperature levels. The difficulties associated with these experiments included the changes in physical properties of the gas mixture when temperature and pressure were varied. Changes in the relative humidity (RH) as a function of pressure and temperature also had a significant effect on the different behaviors of the mobility distributions of particles. In order to accomplish reliable measurement and minimize uncertainties, an integrated on-line control system was utilized. As the pressure decreased in a range of 500-980 hPa, the peak concentration of both ions and nanometer-sized particles decreased, which suggests that higher pressure tended to enhance the growth of particles nucleated by ion-induced nucleation. Moreover, the modal diameters of the measured particle size distributions showed a systematic shift to larger sizes with increasing pressure. However, in the temperature range of 5-20 °C, temperature increases had no significant effects on the mobility distribution of particles. The effects of residence time, RH (7%-70%), and SO(2) concentration (0.08-6.7 ppm) on ion-induced nucleation were also systematically investigated. The results show that the nucleation and growth were significantly dependent on the residence time, RH, and SO(2) concentration, which is in agreement with both a previous model and previous observations. This research will be inevitable for a better understanding of the role of ions in an atmospheric nucleation mechanism.     

On the difficulties of evaluating viscosity/temperature data

Summary Curve fitting, based on the method of least squares, have been carried out on viscosity/temperature data for fluids and solutions. In the course of this work, a number of exponential equations have been tested. It was determined that the WLF equations should not be used since the viscosity temperature coefficients are dependent upon the reference temperature. On the other hand, a thorough statistical analysis shows that it is not possible to make a clear-cut distinction among the 3 parameter exponential equations. Fitting calculations should take into account the fact that most experimental data is of varying goodness and must therefore be weighted. The use of a 4 parameter equation, for example, the Hybrid equation, can only under certain conditions be considered the best viscosity/temperature equation since the statistical variables are not that much better as for 3 parameter equations.

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Zusammenfassung Ausgleichsrechnungen, die auf der Methode der kleinsten Fehlerquadrate beruhen, sind an Viskositäts/TemperaturMeßdaten von Flüssigkeiten und Lösungen durchgeführt worden. Dabei sind eine Reihe von Exponentialgleichungen getestet worden. Es stellte sich heraus, da die WLFGleichung nicht angewendet werden sollte, weil die Temperaturkoeffizienten der Viskosität abhängig sind von der Bezugstemperatur. Andererseits ergibt eine gründliche statistische Analyse, daß eine eindeutige Unterscheidung zwischen den 3-parametrigen Exponentialgleichungen nicht möglich ist. Bei Ausgleichsrechnungen sollte die Tatsache berücksichtigt werden, daß die meisten Meßdaten unterschiedlich fehlerhaft sind und somit gewichtet werden müssen. Die Anwendung einer 4-parametrigen Gleichung, z. B. die der Hybrid-Gleichung, kann nur bedingt als beste Viskositäts/Temperatur-Gleichung angesehen werden, da die statistischen Größen nicht um so viel besser sind als bei den 3-parametrigen Gleichungen.

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With 9 tables     

Pressure dependence of viscosity

We reanalyze the pressure dependence of viscosity of liquids of constant composition under isothermal conditions. Based exclusively on very general considerations concerning the relationship between viscosity and "free volume," we show that, at moderate values of pressure, viscosity increases, as a rule, with increasing pressure, provided the liquid is in stable or metastable (undercooled) equilibrium states. However, even if the behavior of the viscosity is governed by free volume effects, deviations from a positive pressure dependence are possible, when the liquid's thermal expansion coefficient is negative. We derive an equation that allows one to quantitatively determine the pressure dependence of viscosity, which requires, in the simplest case, only the knowledge of the temperature dependence of viscosity at constant pressure, the thermal expansion coefficient, and the isothermal compressibility of the liquid. As an example, the negative pressure dependence of water in the range of temperatures 0-4 degrees C and of several silicate liquids, such as albite, jadeite, dacite, basalts, etc., could be explained in such a way. Other glass-forming liquids initially (for moderate pressures) show a positive pressure dependence of viscosity that changes to a negative one when subjected to high (approximately GPa) isostatic pressure. A detailed analysis of water and already mentioned silicate melts at GPa pressures shows that, in addition to free volume effects, other pressure induced structural transformations may have to be accounted for in a variety of cases. By this reason, the theoretical analysis is extended (i) in order to describe the pressure dependence of viscosity for systems that are in frozen-in thermodynamic nonequilibrium states (glasses, i.e., undercooled liquids below the glass transition temperature Tg) and (ii) to systems which undergo, in addition to variations of the free volume, pressure induced changes of other structural parameters. In such cases a decrease of viscosity with increasing pressure may occur, in principle, even if the thermal expansion coefficient is positive. In this way, the present analysis grants a general tool to estimate the pressure dependence of viscosity and supposedly settles the controversy in the current literature.     

Investigating the temperature dependence of the viscosity of a non-Newtonian fluid within lithographically defined microchannels

We present a study of the rheological phenomenology of a non-Newtonian glass former within hybrid microchannels above the vitrification region. We determined the temperature behavior of the viscosity, which is well fitted by a Vogel-Fulcher-Tamman law for shear rates between 4 x 10(-2) and 9 x 10(-1) s(-1). The microflow viscosity was compared with previously reported conductivity data of the investigated molecular system. Our findings provide an insight into the coupling between the structural dynamics in the bulk and that within the microchannels, suggesting lithographically defined microfluidic systems as promising tools for the investigation of the rheological properties of complex liquids.     

On the temperature dependence of vibrationally induced intensity

The temperature dependence of vibrationally induced transitions is investigated in the general case in which both BO and HT mechanisms are active and it is shown that this can give information about the relative strength of the two mechanisms.     

On the temperature dependence of non-radiative deactivation processes

It is shown that the fluorescence quantum yield depends on temperature rather than on the viscosity of the solvent. The intersystem crossing rate can be described as a sum of a temperature independent and a temperature dependent term. For most of the molecules investigated in this paper the latter can be assumed to have the Arrhenius form. With anthracene, however, significant deviations from the Arrhenius behaviour are observed. With a more general expression involving the density of states the temperature dependence of the fluorescence quantum yield can be satisfactorily described.     

Determination of the vapour pressure temperature dependence of californium hexafluoroacetylacetonate adducts

The temperature dependence of the vapour pressure of californium-249 hexafluoroacetylacetonate adducts with tributylphosphate /TBP/, tributylphosphineoxide /TBPO/ and dipropylsulphoxide /DPSO/ is determined. The enthalpy and entropy sublimation of the compounds are calculated.     

The dependence of craze velocity on the pressure and temperature of the environmental gas

The craze velocity was determined for poly(chlorotrifluoroethylene) (PCTFE) in CH₄ and for PCTFE, polystyrene, and poly(methyl methacrylate) in N₂. It was found that for temperatures near the boiling point the velocity and number of crazes depended on the relative pressure given by P exp[-(Q_v/R) (T_B^?1 - T^?1)], where P is the pressure, Q_v is the heat of vaporization, and T_B is the boiling point. The craze velocity was related to the coverage of the adsorbed gas. For coverages corresponding to a few monolayers the logarithm of the velocity was proportional to the relative pressure. As the temperature increases from T_B, the creep rate decreases because gas desorbs with increasing temperature; the creep rate attains a minimum value at a temperature where the general process of thermally activated deformation becomes dominant.     

On the anomalous temperature dependence of cellulose aqueous solubility

The solubility of cellulose in water-based media is promoted by low temperature, which may appear counter-intuitive. An explanation to this phenomenon has been proposed that is based on a temperature-dependent orientation of the hydroxymethyl group. In this paper, this hypothesis is investigated using molecular dynamics computer simulations and NMR spectroscopy, and is discussed in conjunction with alternative explanations based on solvent–solute and solvent–solvent hydrogen bond formation respectively. It is shown that neither simulations nor experiments lend support to the proposed mechanism based on the hydroxymethyl orientation, whereas the two alternative explanations give rise to two distinct contributions to the hydration free energy of cellooligomers.     

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 T_o 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 V_x(T_o)≡V_o (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 T_o.