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We have performed a combined experimental and theoretical study of the thermodynamic properties of semifluorinated alkanes. In particular, the liquid density of perfluorohexylhexane (F6H6) and perfluorohexyloctane (F6H8) has been measured as a function of temperature from 273.15 to 353.15 K and at four temperatures as a function of pressure up to 600 bar. The results were interpreted using the SAFT-VR equation of state. The perfluoroalkylalkanes were modeled as heterosegmented diblock chains using parameters for the alkyl and perfluoroalkyl segments developed in earlier work. Through this simple approach, we are able to predict the thermodynamic behavior of the perfluoroalkylalkanes studied without fitting to any experimental data for the systems being studied.

Configurational-bias Monte Carlo has been incorporated into the Wang-Landau method. Although the Wang-Landau algorithm enables the calculation of the complete density of states, its applicability to continuous molecular systems has been limited to simple models. With the inclusion of more advanced sampling techniques, such as configurational-bias, the Wang-Landau method can be used to simulate complex chemical systems. The accuracy and efficiency of the method is assessed using as a test case systems of linear alkanes represented by a united-atom model. With strict convergence criteria, the density of states derived from the Wang-Landau algorithm yields the correct heat capacity when compared to conventional Boltzmann sampling simulations. [ABSTRACT FROM AUTHOR]

Shear viscosity of n-decane was computed using the molecular stress transient time correlation function (TTCF) formalism for the wide range of shear rates from 1.7 × 1010 s-1 to 2.13 × 104 s-1. In earlier work calculations were presented for the shear viscosity of n-decane using the atomic stress formalism of the TTCF method (G. Pan and C. McCabe, J. Chem. Phys. 125(19), 4527 (2006)) in which we were able to close the gap between the lowest shear rates accessible by direct nonequilibrium molecular dynamics (NEMD) simulations and the highest shear rates possible in experimental studies. Here it is shown that the application of the molecular stress approach within the TTCF formalism, as an alternative to the atomic stress method, significantly reduces the number of NEMD trajectories necessary to obtain the shear viscosity. [ABSTRACT FROM AUTHOR]

The phase and volumetric behaviour of binary mixtures of n-alkanes and n-perfluoroalkanes at subcritical conditions have been studied using the SAFT–VR equation of state. In previous work [C. McCabe, A. Galindo, A. Gil-Villegas, G. Jackson, Predicting the high-pressure phase equilibria of binary mixtures of perfluoro-n-alkanes plus n-alkanes using the SAFT–VR approach, J. Phys. Chem. B 102 (1998) 8060–8069] the SAFT–VR equation was successfully used to predict the phase behaviour of binary mixtures of low molecular weight n-perfluoroalkanes + n-alkanes. A transferable binary interaction parameter was proposed which enabled the accurate prediction of the critical lines for all the systems studied. In this work we focus on the low pressure liquid–liquid immiscibility displayed by binary mixtures of longer chains (C5ㅡC8). New transferable binary interaction parameters for these mixtures are proposed, based on the reproduction of the UCST and excess volumes for the n-hexane + n-perfluorohexane system. With these parameters, predictions are then made for the vapour–liquid equilibria (VLE), liquid–liquid equilibria (LLE) and excess volumes of other binary mixtures without any additional fitting to experimental data. The resulting predictions from the SAFT–VR equation are in good agreement with the available experimental data. [Copyright &y& Elsevier]

SAFT is perhaps the most versatile, fundamentally, based engineering equation of state in use today. However, in common with all analytic equations of state, SAFT exhibits classical behavior in the critical region rather than the non-analytical, singular behavior seen in real fluids. Recently, so-called crossover equations of state have been developed which solve this shortcoming by incorporating the scaling laws valid asymptotically close to the critical point while reducing to the original classical equation of state far from the critical point. We have combined the SAFT-VR equation of state with an analytical crossover technique to obtain the SAFT-VRX equation of state. The SAFT-VRX approach combines the accurate low temperature behavior of SAFT-VR with a precise representation of the critical region. Preliminary results are presented for hydrocarbon systems which illustrate the accuracy of the SAFT-VRX approach over the entire fluid phase region. [Copyright &y& Elsevier]

The properties of alkanes in the C[sub 20]-C[sub 40] mass range are of fundamental importance in industrial applications as they are important constituents of synthetic lubricant base stocks. In an extension to earlier work on alkanes in the C[sub 20]-C[sub 40] carbon number range we present the results of molecular simulations for 9-octylheptadecane, a starlike isomer of C[sub 25]. Both equilibrium (EMD) and nonequilibrium molecular dynamics (NEMD) simulations have been performed under ambient state conditions and to pressures in the gigapascal range. The EMD simulations focus on calculations of the rotational relaxation times, while the NEMD simulations reveal the dependence of the viscosity on strain rate. Additionally, we calculate the viscosity number and pressure-viscosity coefficient for 9-octylheptadecane and compare the results with those obtained experimentally. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The vapor pressure of four liquidperfluoroalkylalkanes(CF3(CF2)n(CH2)mCH3; n= 3, m= 4,5,7; n= 5, m= 5) was measured as a function of temperature between278 and 328 K. Molar enthalpies of vaporization were calculated fromthe experimental data, and the results were compared with data fromthe literature for the corresponding alkanes and perfluoroalkanes.The heterosegmented statistical associating fluid theory was usedto interpret the results at the molecular level both with and withoutthe explicit inclusion of the dipolar nature of the molecules. Additionally,ab initio calculations were performed for all perfluoroalkylalkanesstudied to determine the dipole moment to be used in the theoreticalcalculations. We demonstrate that the inclusion of a dipolar termis essential for describing the vapor–liquid equilibria ofperfluoroalkylalkanes. It is also shown that vapor–liquidequilibria in these compounds result from a subtle balance betweendipolar interactions, which decrease the vapor pressure, and the relativelyweak dispersive interactions between the hydrogenated and fluorinatedsegments. [ABSTRACT FROM AUTHOR]

Abstract: The viscosity of (hexane+perfluorohexane) mixtures has been measured at 298K, 303K and 308K, over the whole composition range. The results show large negative deviations from the arithmetic mean of the viscosities of the pure components, reaching −17% at x(perfluorohexane)=0.7. To obtain molecular level insight into the behaviour of the system, all-atom molecular dynamics simulations have been performed and used to calculate the viscosities, radial distribution functions, and rotational relaxation times of the studied (hexane+perfluorohexane) mixtures. This is the first effort to assess the effect of mixing hydrogenated and fluorinated molecules in the viscosity. [Copyright &y& Elsevier]

As part of a combined experimental and theoretical study of the thermodynamic properties of perfluoroalkylalkanes (PFAAs), the liquid density of perfluorobutylpentane (F4H5), perfluorobutylhexane (F4H6), and perfluorobutyloctane (F4H8) was measured as a function of temperature from 278.15 to 353.15 K and from atmospheric pressure to 70 MPa. The liquid densities of n-perfluoropentane, n-perfluorohexane, n-perfluorooctane, and n-perfluorononane were also measured at room pressure over the same temperature range. The PVT behavior of the PFAAs was also studied using the SAFT-VR equation of state. The PFAA molecules were modeled as heterosegmented diblock chains, using different parameters for the alkyl and perfluoroalkyl segments, that were developed in earlier work. Through this simple approach, we are able to predict the thermodynamic behavior of the perfluoroalkylalkanes, without fitting to any experimental data for the systems being studied. Molecular dynamics simulations have also been performed and used to calculate the densities of the perfluoroalkylalkanes studied. [ABSTRACT FROM AUTHOR]

As part of a systematic study of the thermophysical properties of two important classes of fluorinated organic compounds (perfluoroalkanes and perfluoroalkylalkanes), viscosity measurements of four n-perfluoroalkanes and five perfluoroalkylalkanes have been carried out at atmospheric pressure and over a wide range of temperatures (278–353 K). From the experimental results the contribution to the viscosity from the CF2and CF3groups as a function of temperature have been estimated. Similarly, the contributions for CH2and CH3groups in n-alkanes have been determined using literature data. For perfluoroalkylalkanes, the viscosity results were interpreted in terms of the contributions of the constituent CF2, CF3, CH2, and CH3groups, the deviations from ideality on mixing hydrogenated and fluorinated chains, and the contribution due to the formation of the CF2–CH2bond. A standard empirical group contribution method (Sastri–Rao method) has also been used to estimate the viscosities of the perfluoroalkylalkanes. Finally, to obtain molecular level insight into the behavior of these molecules, all-atom molecular dynamics simulations have been performed and used to calculate the densities and viscosities of the perfluoroalkylalkanes studied. Although both quantities are underestimated compared to the experimental data, with the viscosities showing the largest deviations, the trends observed in the experimental viscosities are captured. [ABSTRACT FROM AUTHOR]

Abstract: Partial molar volumes at infinite dilution have been obtained for 3 perfluoroalkylalkanes (PFAA) in n-octane at 298.15K from experimental apparent molal volumes. The results were interpreted estimating the contributions of the hydrogenated and perfluorinated segments to the partial molar volume. For this reason, partial molar volumes at infinite dilution for 3 perfluoroalkanes (PFA) in n-octane at 298.15K have also been obtained. The results were further interpreted using the hetero-SAFT-VR equation of state, which models the perfluoroalkylalkanes as heterosegmented di-block chains. The cross interactions, both intra and intermolecular, were characterised using parameters developed in earlier studies for (alkane+perfluoroalkane) mixtures: the calculations are thus fully predictive. The theory is able to accurately predict the volumetric behaviour of the solutions of perfluoroalkylalkanes, without fitting to any experimental data. [Copyright &y& Elsevier]

Abstract: In previous work, we developed the crossover SAFT–VR equation of state (SAFT–VRX) for pure fluids by following the crossover approach proposed by Kiselev. The SAFT–VRX equation was shown to be very accurate in the prediction of PVT and phase behaviour for both non-associating and associating fluids. In particular, simple expressions for the potential model parameters for the n-alkane homologous series were developed, allowing the prediction of the thermodynamic properties without fitting to experimental data. In this work, we have applied the SAFT–VRX equation to binary mixtures of short-chain n-alkanes, using the prescriptions for the model parameters developed previously to determine the pure fluid parameters. The SAFT–VRX equation is found to accurately predict the gas–liquid critical locus and vapor–liquid equilibrium data for the systems studied without fitting to binary experimental mixture data. [Copyright &y& Elsevier]

The saturation vapour pressure of {x BF3 + (1−x)n-C4H10} has been measured at 195.49 K. The system shows large positive deviations from Raoult’s law and liquid–liquid immiscibility over a wide composition range whose limits have been estimated as 0.39±0.030.9785. The excess molar Gibbs energies (GmE) have been calculated as a function of composition from the vapour pressure data. For the hypothetical equimolar mixture GmE (x=0.5) = (703.9±29) J mol−1. The results were interpreted using the statistical associating fluid theory for potentials of variable range (SAFT-VR), as well as compared with those of related systems, such as (BF3 + n-pentane) and (BF3 + xenon). [Copyright &y& Elsevier]