Masaharu Ohba

Thermodynamic properties of rigid polycyclic molecules. 1: Enthalpies of solution of fused ring polycyclic aromatic hydrocarbons

Abstract Enthalpies of solution, Δ sol H , have been measured by using an adiabatic calorimeter, in order to explain thermal stabilization of fused ring polycyclic aromatic hydrocarbon in solution process. Solutes used were benzene, naphthalene, anthracene, phenanthrene, naphthacene and chrysene. Solvents used were cyclohexane, heptane, 1,4-dioxane, benzene and chloroform. The solution process of benzene was endothermic for heptane and cyclohexane, almost athermal for dioxane, and slightly exothermic for chloroform. The Δ sol H results for all other solid solutes were large positive values for all solvents. The results for solid solutes show the good correlation with enthalpy of fusion. Enthalpies of solvation, Δ solv H , were estimated by subtracting enthalpy of sublimation from Δ sol H . The results show a linear dependence on the number of carbon atoms in solute molecule through near the origin.

The asymptotic behavior of the site-site Ornstein-Zernike equation and RISM-2 approximations for polyatomic molecular fluids

It is shown that the asymptotic properties of the reference interaction site model (RISM)-2 type integral equations for polyatomic molecular fluids are quite similar to those of simple fluids. The exact asymptotic form of the new site-site direct correlation function C αγ ( r ), which is defined by the site-site Ornstein-Zernike equation, is given by using the exact asymptotic form of the site-site total correlation function. The result is C αγ ( r )≃- U (1, 2)/ k B T for nonpolar fluids composed of homonuclear diatomic molecules as well as heteronuclear diatomic molecules, where U (1, 2) is an intermolecular potential, k B the Boltzmann constant and T the absolute temperature. The asymptotic form of C αγ ( r ) given by the RISM-2 approximations is found to be in accordance with the exact result. Thus, the RISM-2 theory is concluded to have no theoretical inconsistency like that in the RISM-1 theory.

Study of polar dumbbell fluids from the gaseous to the liquid densities by the reference interaction site model‐1 and ‐2 integral equations

The structures and the thermodynamic properties of a fluid composed of a nonpolar or a polar dumbbell molecule have been studied from the gaslike to the liquidlike density regions based on two types of the reference interaction site model (RISM) integral equation theories (RISM‐1 and RISM‐2). This is the first application of the RISM‐2 theory to a polar dumbbell fluid. We have proven that the RISM‐2 theory with the hypernetted‐chain (HNC) approximation has an inconsistency with respect to the zeroth‐order relation between site–site total correlation functions and site–site direct correlation functions in the Fourier space. An hypothetical bridge function is introduced to remedy this inconsistency, which works well to give good information on the structure and the dielectric constant in the lower‐density region. On the other hand, the RISM‐1 theory works well in the higher‐density region, but not well in the lower‐density region. Complemental application of these theories, that is, the RISM‐1 theory for th...

The shapes of critical loci of binary fluid mixtures on the p – T plane

The relations between the shapes of the critical loci of binary fluid mixtures and the positions of the critical points of their component fluids on the p–T plane were considered theoretically. The consideration was carried out for vapor–liquid phase equilibria in the model systems without liquid–liquid equilibria. We focused only the relations between the shapes and the tangent of the straight lines connecting the critical points of the component fluids on the p–T plane, and so the effects of the distance between the critical points were out of the scope of this work. The changes in the shapes of the critical loci were classified logically into three patterns. Literature survey has shown that the two patterns exist in the experimental results for several types of mixtures. The shapes of the critical loci of the binary fluid mixtures on the p–T plane are closely related to the relative positions between the critical points of their component fluids.

Thermodynamic properties of rigid polycyclic molecules. (2) Partial molar volumes of polycyclic aromatics compared with the rism integral equation theory

Partial molar volumes of polycyclic aromatics (benzene, naphthalene, anthracene, phenanthrene, chrysene, diphenyl, o-, m-, p-terphenyl) at infinite dilution were measured. The additivity rule with respect to the number of aromatic rings holds very accurately for the set of solute molecules of benzene, naphthalene and phenanthrene, as well as the set of benzene, diphenyl, and p-terphenyl. The linearity of the set of data of benzene, naphthalene and anthracene is slightly worse. The fact that the additivity rule holds including monomer for these series of polycyclic aromatics makes a sharp contrast with the case of n-alkane, where the partial molar volume of methane is somewhat larger than the value expected from the additivity rule. In order to explore the origin of this difference, theoretical calculations were made for model chain molecules. The calculated result suggests that this difference between polycyclic aromatics and n-alkane is not caused by the size difference between monomer and solvent molecule. The partial molar volume of isomers of terphenyl becomes smaller as the molecule takes more stretched form, which is quite opposite to many other compounds. This peculiar behavior is referred to the increase of dihedral angle between two aromatic rings along with the decrease of bond angle.

Density dependence of solvation properties in polar dumbbell fluids from gaseous to liquid densities

The solvent density dependence of the solvation energy difference associated with a charge transfer process in a polar dumbbell fluid is studied from the gaslike to the liquidlike densities by means of two types of the integral equation theories and the Monte Carlo simulation. The polar dumbbell fluid model including the Coulombic interaction explicitly has succeeded in a qualitative reproduction of quite a larger density dependence of the solvation energy in the low-density region than that in the higher-density region. The origin of the density dependence has been attributed to the difference in the reaction field response at various densities. At the low density, the reaction field shows a highly enhanced nonlinear response to the solute dipole moment. The nonlinear enhancement is an intrinsic nature in the gaseous dielectric solvation, and is due to the enhanced local density around the solute molecule with increasing the solute charge. On the other hand, the reaction field at the high density respond...

The dielectric constant and the site-site direct correlation function of the RISM-2 theory for polar polyatomic molecular fluids

The exact expression of the dielectric constant for polar polyatomic molecular fluids is obtained in terms of the site-site direct correlation function. This equation is closely related to the formula of the dielectric constant in terms of the molecular direct correlation function (the Ramshaw equation, Ramshaw, 1972, J. chem. Phys., 57, 2684). We discuss why RISM-1 theory gives a trivial expression for the dielectric constant using equations obtained here, and show that RISM-2 theory leads to a non-trivial result for the dielectric constant of molecular liquids.

The second dielectric virial coefficient of non-ideal polar hard-sphere fluids and polar hard dumb-bell fluids

The second dielectric virial coefficient, B ϵ, of fluids is calculated for the two liquids: non-ideal polar hard-spheres (two point charges +q and -q are embedded in the hard-sphere); polar hard dumb-bells. B ϵ depends sensitively on the shape of molecule. B ϵ for the non-ideal polar hard-sphere fluids is a positive value, and increases with separation of two charges. On the other hand, B ϵ for polar hard dumb-bell fluids decreases, becoming negative with the increasing length of the molecules. This behaviour agrees with the experimental results.

The second dielectric virial coefficient of asymmetrical polar hard dumb-bell fluids

We have calculated the second dielectric virial coefficient B ϵ of some asymmetrical polar hard dumb-bell fluids. In the case of molecules with a short bond length, the effect of the asymmetry of molecular shapes is to increase B ϵ. In contrast, for molecules with a long bond length, the effect is to decrease B ϵ gradually.

Pressure and temperature dependence of excess thermodynamic quantities of Lennard–Jones binary mixtures

Abstract The PY-integral equation has been applied for the model system consisting of monatomic molecules A and B obeying the Lennard–Jones potential law so as to establish the molecular basis for interpretation of excess thermodynamic quantities of solutions. The potential parameters used are σ A A =1.0 and σ B B =0.9283, as well as e A A =1.0 and e B B =0.8. These parameters are set as σ A A /( σ B B ) 3 = e A A / e B B . The critical parameters of these fluids are known to be ( P c , T c )=(0.129, 1.32) for species A and (0.129, 1.06) for species B and calculation has been carried out in the region where pressure and temperature are simultaneously below the critical values. The formalism proposed recently by Ohba and Nomura (J. Phys. Chem., 99, 12355 (1995)) has been adopted and the excess thermodynamic quantities such as excess volume V E , excess enthalpies H E , and excess specific heat capacities Cp E have been evaluated. Pressure dependence was one order of magnitude smaller than the case of temperature dependence and that the change of temperature from 0.95 to 1.0 gives rise to far more remarkable effect on the excess quantities than for the temperature change from T =0.8 to 0.9. The components contributing to the partial molecular enthalpy and the specific heat capacity have been evaluated.