Takayo Takigawa

Thermoynamic properties (HmE, CP,mE, VmE, κTE) of binary mixtures {x1,3-Dioxane + (1−x)Cyclohexane} at 298.15 K

Abstract Molar excess enthalpies HmE, isobaric heat capacities CP,mE, volumes VmE and isothermal compressibilities κTE for the 1,3-dioxane(3DX) + cyclohexane mixture were measured at 298.15 K, in order to compare to those of the 1,4-dioxane(4DX) + cyclohexane mixture. HmE is endothermic and the maximum value about 1.5 kJ mol−1 at x ≈ 0.45, and lower than that of the 4DX mixture by about 80 J mol−1. VmE is positive over the whole concentration and the maximum value is about 0.85 cm3 mol−1 at x ≈ 0.45, and lower than that of the 4DX mixture. The above results suggest the energetic unstabilization, resulting in the volume expansion in the mixture. CP,mE shows the characteristic W-shaped concentration dependence, which has maximum at x ≈ 0.45 and two minima at x ≈ 0.1 and 0.9. The maximum CP,mE value for 3DX mixture shifts toward the positive side, compared to that of 4DX mixture. κTE were estimated from speeds of sound, densities, thermal expansion coefficients and isobaric heat capacities of the pure component liquids and the mixtures. The κTE result shows the positive concentration dependence over the whole composition range. The 3DX mixture has the similar thermodynamic properties to the 4DX mixture, despite that 4DX is the nonpolar solvent and 3DX is the dipolar liquid. this means that there exists the local dipolar interaction between 4DX molecules, and the prevalence of “microheterogeneity” in the both mixtures.

Excess enthalpies of binary mixtures {xdioxane isomer+(1−x)non-polar liquid} at 298.15 K

Abstract Molar excess enthalpies H m E have been measured at 298.15 K for binary mixtures {1,3-dioxane or 1,4-dioxane+cyclohexane or n -pentane or 2,2,4-trimethylpentane or tetrachloroethene or benzene} by using a home-made flow calorimeter constructed newly for determining excess enthalpy in the dilute concentration range. The positive H m E for alkane and cycloalkane systems were found. Those of the benzene systems were exothermic except for the 1,4-dioxane rich region. The experimental result was discussed qualitatively in view of intermolecular interactions in mixtures and the isomer effect on thermodynamic properties of dioxane mixtures.

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.

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.