On the temperature and pressure dependence of the dynamic viscosity of n-alkanes

Isotherms of the coefficient of dynamic viscosity and isobars of n-alkanes are considered. One-parameter correlations for the isobars are constructed based on the literature data. A linear correlation is revealed between the boiling and melting temperatures and the found parameter of the baric dependence of viscosity for a homological series of alkanes.     

Studies on the relative temperature viscosity coefficient of nitrobenzene in n-hexane and n-heptane near the temperature of phase separation

The viscosity coefficient η of nitrobenzene in n-hexane and n-heptane was measured as a function of concentration and temperature near the te     

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     

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%.     

On the viscosity Arrhenius temperature for methanol + N,N-dimethylformamide binary mixtures over the temperature range from 303.15 to 323.15 K

Excess properties calculated from literature values of experimental density and viscosity in N,N-dimethylformamide (DMF) + methanol (Met) binary mixtures (from 303.15 to 323.15 K) can lead us to test different correlation equations as well as their corresponding derivative properties. Inspection of the Arrhenius activation energy (E_a) and the enthalpy (ΔH*) of activation of viscous flow shows very close values; here, we can define partial molar activation energies E_a1 and E_a2 for N,N-DMF and Met, respectively, along with their individual contribution separately. Correlation between the two Arrhenius parameters of viscosity in all compositions shows existence of main distinct interaction behaviours delimited by particular mole fractions in N,N-DMF. In addition, we add that correlation between Arrhenius parameters reveals interesting Arrhenius temperature that is closely related to the vaporisation temperature in the liquid vapour equilibrium, and the limiting corresponding partial molar properties can permit us to estimate the boiling points of the pure components.     

Effect of temperature on the intrinsic viscosity and conformation of different pectins

The effects of temperature on the intrinsic viscosity and on the conformation of pectin obtained from Citrus, Apple and Sunflower in a 0.17M NaCl solution were studied. Mark-Houwink plots for Orange, Apple and Sunflower pectin were obtained using HPSEC with online light scattering and viscosity detection. The intrinsic viscosity and flow activation energy E _a of pectin from the sources studied were measured over the temperature range 20–60°C. E _a values were 0.67, 0.69, 1.34, and 1.44 × 10⁷ J/(kmol) for commercial Citrus, Orange, Sunflower and Apple pectin, respectively. Intrinsic viscosity decreased linearly with increasing temperature, for all pectins except Apple one. These results clearly indicated that Apple pectin underwent structural changes that were more drastic than those that occurred for pectin from the other sources. E _a increased with decreasing weight average molar mass M _w indicating that pectin with low M _w were more asymmetric than pectin with higher values of M _w. Changes in the Huggins coefficients K _h with temperature for pectin from the various sources were attributed to the ability of pectin to aggregate, disaggregate and re-aggregate according to the temperature at which it was stored.     

Use of an automatic data quality control algorithm for crude oil viscosity data

When building correlations for physical properties, the data used must be quality controlled to ensure suitable performance of regression procedures and provide acceptable predictions. When using data from different sources and large datasets, this screening could become tedious and laborious unless a systematic and automated consistency check is used.For this study, we had a database of almost 3000 records of PVT properties and black-oil viscosity data coming from 324 differential liberation tests performed in different commercial laboratories.We developed a procedure to “clean up” the data on a test basis, before processing it with a regression routine. We individually screened each test, identified outlying observations and removed those from the regression calculations.The criteria used to discard data relied on the numerical evaluation of the first derivative of selected functions of one variable. If the physical behavior is predicted correctly, these functions should be monotonic. For example oil viscosity (observed function) should always increase as the pressure in the differential liberation tests decreases. Forward and backward derivatives were used to account for the end points. The filtered data resulting from this quality control process consisted of 2324 observations.The data were used to adapt two commonly used compositional viscosity models, Pedersen’s and Lohrenz, Bray and Clark (LBC), such that these models can be used for black-oil systems when compositional data are missing. The oil viscosity ranged from 0.13 to 78.3 cP, with pressure from 14.7 to 5602 psia (0.1–38.62 MPa) and temperature from 537 to 766 R (298–425.55 K). The oil specific gravity ranged from 0.389 to 0.921. These models were validated against an independent dataset consisting of 150 observations. The two models had lower statistical errors than currently available correlations.     

Fictive temperature, cooling rate, and viscosity of glasses

The physical correlation between the fictive temperature dependence of the cooling rate of the melts and the temperature dependence of the equilibrium viscosity has been found by doing differential scanning calorimetric and viscometric measurements on a silicate melt, and by performing finite element simulations of the fiber drawing from that melt. This correlation is governed by a correlation factor Kc (in Pa K) which is constant and universal for silicate glasses. The factor Kc is obtained in the cooling rate range from 10(-2) to 10(6) K/s and is in good agreement with that theoretically predicted. The physical feature of the correlation is discussed in the paper. When the fictive temperature equals the actual temperature, a linear relation exists between the cooling rate and the Maxwell relaxation rate, the slope of which depends on the fragility of the glass melts. The Avramov equation is extended to describe the cooling rate dependence of the fictive temperature. The cooling rate equation contains only one adjusting parameter, i.e., the fragility parameter alpha.     

Theoretical modeling for thermophysical properties of cellulose: pressure/volume/temperature data

Thermo-compression process—compression of pure cellulose under high temperatures and pressures—is a recent method to produce biodegradable materials. For such processes, experimental measurements and study of properties and behavior of cellulose are difficult to carry out. To overcome these difficulties, a complete pressure–volume–temperature investigation is needed as carried out in this work. To develop a predictive thermodynamic PVT model of cellulose theoretically, the modified Sanchez and Lacombe equation of state together with the implementation of the Hoftyzer and van Krevelen group contribution method and the Boudouris modification to the Constantinou and Gani’s group contribution method were coupled to the Compressible Regular Solution theory. The developed method is a pure predictive model and to examine the accuracy of theoretically calculated PVT data by the model, some available PVT data of cellulose at temperatures from 25 to 180 °C and pressures from 19.6 to 196 MPa (219 data points) were collected from literature. The comparisons were made and the agreement between the calculations and the experimental data were acceptable with a Cumulative Absolute Relative Deviation of 0.04 %. Consequently, the model can be used for prediction of thermodynamic properties of cellulose and cellulose-containing mixtures.     

Practical digest for evaluating the uncertainty of analytical assays from validation data according to the LGC/VAM protocol

The estimation of the measurement uncertainty of analytical assays based on the LGC/VAM protocol from validation data is fully revisited and discussed in the light of the study of precision, trueness and robustness.     

Analysis of intrinsic viscosity data on polyacrylonitrile in various solvents

Summary In the preceding paper, a method was proposed for interpreting quantitatively intrinsic viscosity data in terms of the parameters expressing the contributions of the excluded volume effect and the partially free draining effect, respectively. The purpose of this paper is mainly to demonstrate the usefulness of the method in obtaining wide ranges of informations concerning the dimensions of a polymer chain and the polymer-solvent interactions, without recourse to more laborious experiments usually made. Merely intrinsic viscosities of an unfractionated polyacrylonitrile (PAN) have been measured in various solvents at 30 and 50 °C, which is necessary and sufficient for this line of analysis. The solvents used were dimethylformamide (DMF), aqueous solutions of zinc chloride in the concentration range, 5770%, mixtures of dimethylsulfoxide (DMSO) and acetone in the range, 60100 vol.% of DMSO, and aqueous solutions of perchloric acid at the concentrations, 55 and 65%. First of all, making use of the parameters in theMark-Houwink equation obtained for two different solvents, quantitative discussions have become possible, with fair success, on the contributions of the draining effect and the excluded volume effect to the intrinsic viscosities of PAN solutions. The consideration of the draining effect, as well as of the differences in molecular heterogeneity, seems capable of accounting for considerably wide discrepancies in theMark-Houwink constants among several literatures on PAN in DMF. Next, making use of theMark-Houwink constants, theFlory's parameterK was evaluated (K=1.256 × 10^–3 at 35 °C), from which the dimensions of the PAN chain were discussed. Furthermore, theMark-Houwink constants were calculated for the various solvents from the intrinsic viscosity of the single sample. Finally, the thermodynamic interactions of the polymer with the various solvents were discussed in terms of the parameters appearing in the theory ofFlory andFox. In all cases studied, the heat of dilution parameter and even the entropy of dilution parameter are negative, indicating strong attractive interactions between them.

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Zusammenfassung In der Arbeit wird eine Methode vorgeschlagen zur quantitativen Interpretation von Daten der intrinsic-Viskosität in Parametern, die die Beiträge des ausgeschlossenen Volumens und die teilweise Durchspülung betreffen. Der Sinn dieser Arbeit ist hauptsächlich, den Nutzen der Methode zu beweisen, weitere Informationen über die Dimension einer Polymerenkette und die Wechselwirkung von Polymer-Lösungsmittel ohne Rückgriff auf die normalen aufwendigeren Untersuchungen zu erhalten. Es wurden einfach intrinsic-Viskositäten von unfraktioniertem Polyacrylnitril (PAN) in verschiedenen Lösungsmitteln bei 30 und 50° C gemessen, die notwendig und ausreichend für diese Analysen sind. Lösungsmittel waren Dimethylformamid (DMF), wäßrige Lösungen von Zinkchlorid im Konzentrationsbereich 57–70% gemischt mit Dimethylsulfoxyd (DMSO) und Aceton im Bereich 60–100 Volumen-% von DMSO und wäßrige Lösungen von perchloriger Säure in Konzentrationen von 55–65%. Zunächst, indem von den Parametern derMark-Houwink-Gleichung aus zwei verschiedenen Lösungsmitteln Gebrauch gemacht wurde, wurden quantitative Diskussionen mit gutem Erfolg über den Beitrag der Durchspülung und den Effekt des ausgeschlossenen Volumens möglich. Die Betrachtung der Durchspülung wie auch der Unterschiede in molekularer Heterogenität scheint für beträchtlich starke Diskrepanzen derMark-Houwink-Konstanten aus der Literatur über PAN in DMF verantwortlich zu sein. Aus denMark-Houwink-Konstanten läßt sichFlorys ParameterK ermitteln (K=1.256 · 10^–3 bei 35 °C), aus dem die Dimension der PAN-Kette folgt. Weiter wurden dieMark-Houwink-Konstanten für die intrinsic-Viskosität in verschiedenen Lösungsmitteln für eine einzelne Probe berechnet. Schließlich läßt sich die thermodynamische Wechselwirkung dieses Polymers mit verschiedenen Lösungsmitteln in Parametern diskutieren, die in der Theorie vonFlory undFox erscheinen. In allen untersuchten Fällen ist die Verdünnungswärme und auch die Verdünnungsentropie negativ, was auf eine starke Wechselwirkung schließen läßt.

     

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.     

气化中煤灰熔点和黏度预测模型

根据煤灰中硅铝含量及硅铝比对煤灰进行分类研究,构建了灰熔融点和黏度与组分关系的优化模型,并对宽组分范围的煤灰熔点、黏度关系进行探讨。获得了更加精确的灰熔点预测模型,全液相温度模型预测误差为±40℃,实验值和预测值的标准误差为25℃。采用修正的Urbain模型和Roscoe模型相结合,模型预测值和实验值吻合较好,低黏度下对数黏度的预测值和实验值误差为±0.1;高黏度下黏度的预测值和实验值误差为±0.2。结果表明,基于煤灰组分分类的拟合结果优于涵盖宽组分的模型。     

On the Adam-Gibbs-Kirkpatrick-Thirumalai-Wolynes scenario for the viscosity increase in glasses

We reformulate the interpretation of the mean-field glass transition scenario for finite dimensional systems, proposed by Kirkpatrick, Thirumalai, and Wolynes (KTW). This allows us to establish clearly a temperature dependent length xi( *) above which the mean-field glass transition picture has to be modified. We argue in favor of the mosaic state introduced by KTW, which leads to the Adam-Gibbs relation between the viscosity and configurational entropy of glass forming liquids. Our argument is a mixture of thermodynamics and kinetics, partly inspired by the random energy model: small clusters of particles are thermodynamically frozen in low energy states, whereas large clusters are kinetically frozen by large activation energies. The relevant relaxation time is that of the smallest "liquid" clusters. Some physical consequences are discussed.