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  • 1995-1999  (7)
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  • 1
    Electronic Resource
    Electronic Resource
    Excess properties of mixtures of n-alkanes from perturbation theory (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3192-3202 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Excess properties of binary mixtures of n-alkanes have been evaluated from perturbation theory. A good equation of state for the reference system mixture is combined with a simple approximation to the perturbation term and with a reasonable set of potential parameters to yield a qualitatively correct description of the trends of excess volumes and excess Gibbs energies of n-alkane mixtures without the need for any adjustable parameter. Moreover, the theory can be made quantitative by introducing two adjustable parameters for each temperature. These two parameters have a clear molecular origin and they could be removed if some of the approximations of the theory proposed here were replaced by a more rigorous evaluation. In this sense this paper is just a first step toward a fully molecular theory of excess properties of alkanes. Excess properties estimated from perturbation theory by using these two adjustable parameters are in excellent agreement with experiment and are clearly superior to those obtained from the classic FOV theory proposed by Flory, Orwoll and Vrij [J. Am. Chem. Soc. 86, 3507, 3515 (1964)]. It is our view that the theory of this work is also conceptually superior to the FOV theory, since it rests on a more rigorous molecular basis. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479599
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Critical properties of mixtures of alkanes from perturbation theory (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3183-3191 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The critical properties of binary mixtures of linear and branched alkanes have been evaluated using perturbation theory. An accurate equation of state for the reference system is combined with a mean field treatment of the perturbation term, along with a reasonable potential model. No adjustable parameters were used either for the pure compounds or for the binary mixtures. The aim of this work is to show which features of the critical properties of alkane mixtures can be obtained from a fully molecular based theory. It is shown that the main trends of the critical properties of alkane binary mixtures can be described qualitatively by the theory. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479598
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  • 3
    Electronic Resource
    Electronic Resource
    Vapor–liquid equilibria of linear and branched alkanes from perturbation theory (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 5681-5690 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vapor–liquid equilibrium properties of linear and branched alkanes with up to eight carbon atoms have been determined by means of a simple perturbation theory. An accurate equation of state for the reference system is combined with a mean field treatment of the perturbation term, along with a reasonable set of potential parameters. Experimental trends of the critical properties of alkanes are described qualitatively by the theory. In particular, the maximum in the critical pressure and density of linear alkanes as a function of the number of carbon atoms is reproduced and explained on a simple basis. The effect of branching on the critical properties is considered and it is found that the decrease in the critical temperature with branching is correctly predicted. With a few exceptions for some substances, other general trends in critical pressure and density are predicted and explained. The effect of branching on the principle of corresponding states is also studied, in particular on the coexistence densities and vapor pressures. It is found that branching reduces the slope of the vapor pressure curve and makes the coexistence curve narrower when these magnitudes are represented in a corresponding states plot. It is shown that a simple mean field theory is able to describe qualitatively the variation in the critical properties of linear and branched alkanes. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477186
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  • 4
    Electronic Resource
    Electronic Resource
    The second virial coefficient of hard alkane models (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 5670-5680 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The second virial coefficient for hard models of alkanes and other flexible molecules is determined numerically using a new algorithm which increases the speed of the calculations by a few orders of magnitude. For alkanes with few carbon atoms, linear and branched chains were considered and the effect of branching was analyzed. For linear hard alkanes, the second virial coefficient was computed for chains with up to 600 carbon atoms and the scaling behavior was studied. The effect of changes in the chemical structure of a flexible molecule (i.e., bond length, bond angle) was also studied. A fast and efficient empirical methodology to estimate the second virial coefficient of hard chains is given. This methodology uses ideas of convex body geometry. It is shown that the proposed methodology yields very good estimates of the second virial coefficient for chains with up to 100 monomer units, but it predicts incorrectly the scaling law. The virial coefficients provided in this work can be useful in the search of an equation of state for hard alkanes, since it is likely that a good equation of state should provide good estimates of the second virial coefficient. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477185
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  • 5
    Electronic Resource
    Electronic Resource
    Equation of state for hard n-alkane models: Long chains (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 701-713 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An equation of state (EOS) for hard n-alkane models is proposed. This equation requires a previous knowledge of the second virial coefficient of the hard n-alkane model. Since the numerical determination of the second virial coefficient of chain molecules is computationally expensive, a new method for estimating the second virial coefficient of hard polymer models is proposed. This method yields predictions for the second virial coefficients in very good agreement with those determined numerically. In order to test the proposed equation of state, molecular dynamics simulations for repulsive n-alkane chains were performed. Excellent agreement was found between theoretical and simulated pressures for n-alkanes with up to 100 monomer units. The effect of changes in the torsional potential, bond angle, and bond length, on the equation of state of hard n-alkane models is analyzed. The equation of state is also extended to mixtures of hard n-alkane models. The proposed methodology provides an accurate equation of state for realistic models of hard n-alkane molecules. An empirical formula describing the EOS of repulsive n-alkane chains is given. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470867
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  • 6
    Electronic Resource
    Electronic Resource
    Nonequilibrium properties of linear polar Kihara fluids from molecular dynamics. Results for models and for liquid acetonitrile (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 2034-2045 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics simulations for polar Kihara fluids are reported for linear models of different lengths at several dipole and quadrupole values and at three different thermodynamic states. Two of these states are close to the vapor–liquid equilibrium curve and the third one is at the same density as the first and at the same temperature as the second. Self-correlation functions and translational and orientational times are calculated and analyzed. Transport properties, diffusion, thermal conductivity, and shear viscosity are also reported and discussed in terms of multipolar forces. Correlation terms are used to calculate band broadening in different kinds of molecular spectra. Finally, it is shown how it is possible to discriminate between two models of acetonitrile that fit equilibrium properties equally well by using dynamic properties. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474554
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  • 7
    Electronic Resource
    Electronic Resource
    Dynamical properties and transport coefficients of Kihara linear fluids (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 4753-4767 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Transport properties of spherical and linear molecules modeled by the Kihara potential are studied by molecular dynamics simulations. Diffusion coefficients, shear viscosities, and thermal conductivities are calculated for a wide range of the fluid region and for several elongations. The corresponding individual and collective correlation functions are discussed along with angular velocity and reorientational correlation functions. Relaxation times and simple models relevant to orientational motion are also studied. The results obtained are discussed in a corresponding states framework, using previous Gibbs ensemble Monte Carlo data for the liquid–vapor equilibria of the models. In this way, the role of elongation can be studied. It is found that in most of the liquid region, the diffusion coefficient is weakly dependent on elongation. On the other hand, both viscosity and thermal conductivity are found to decrease with elongation. The dependence of transport coefficients on density and temperature is also discussed. On testing the Stokes–Einstein relation, it was observed that, unlike previous findings for hard spheres, stick boundary conditions perform just as good as slip boundary conditions for the Lennard-Jones fluid and the low-elongated Kihara fluid. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473473
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