Ultrasonic nonlinear parameters and sound speed of alcohol-water mixtures

Changes in the nonlinear parameter B/A caused by the addition of monohydric alcohols to water have been investigated. The measurements, made by using an aqueous solution of n-propanol, isopropanol, and t-butanol, show that as the alcohol concentration is increased, B/A decreases to a minimum at approximately 10% concentration (by volume). Further increase in alcohol concentration raises B/A rapidly to a maximum at about 80% by volume. This complex variation in B/A is attributed to solute-solvent interaction which is believed to be due to an enhancement of water structure in the water-rich region. These results suggest that the magnitude of B/A may be closely related to the quasilattice structure of water, which to a first approximation can be expressed by relative amounts of bound and unbound water.     

Tuning phase transitions and realization of special thermodynamic states in alcohol-water mixtures by the addition of ions

We demonstrate with the aid of visual investigations that multiply reentrant liquid-liquid transitions can be obtained in ethyl alcohol (E) - water (W) mixtures, by the addition of ions. Multiplicity of reentrance can be tuned by changing the concentration, size, or the structure forming ability of the ions added. This is a route to the realization of various thermodynamic states, such as special critical points (SCPs), in the vanishing limit of reentrance. We show that in E+W+ ion systems, one can achieve a plait point, a critical double point, a double critical point, and a critical inflection point, in addition to a line of critical points. We adduce evidence for the presence of supramolecular structures and the associated nanoscopic length scale in these systems, by small angle X-ray scattering experiments. Structuring gives rise to the intriguing phase behavior and renders these systems potentially significant to study the role of supramolecular structuring on the approach to asymptotic Ising criticality near SCPs.     

Molecular interactions in ternary organic liquid mixtures

Excess volumes (V₁₂₃^E) of five ternary mixtures were measured at 303.15 K. The mixtures include acetophenone and 1-propanol as common components. The non-common components chosen in the present investigation are benzene, toluene, chlorobenzene, bromobenzene and nitrobenzene. The measured excess volume data are negative over the entire composition range in the mixtures containing chlorobenzene, bromobenzene and nitrobenzene. On the other hand, the quantity exhibits an inversion in sign in the remaining two mixtures. The experimental results were compared with those predicted by empirical relations.     

Molecular structure of nuclei

Cluster structures of nuclei are discussed, with emphasis on nuclear clustering in unstable nuclei. The subjects we discuss are alpha condensed states, clustering in Be and B isotopes, and clustering in ³²Mg and ³⁰Ne. The subject of alpha cluster condensation comes from the clustering nature of dilute nuclear matter. We discuss that recent heavy-ion central collision experiments give us nice evidence of the clustering in dilute nuclear matter. We then present a new prediction of the existence of the “alpha cluster condensed states” in the self-conjugate 4n nuclei around the breakup threshold energy into n alpha-particles. As for the clustering in neutron-rich Be, we discuss the comparison between the antisymmetrized molecular-dynamics results and the recent experimental data, which shows that the clustering feature manifests itself very clearly in neutron-rich Be isotopes both in the ground and excited states. Clustering in Be isotopes near neutron dripline is intimately related to the breaking of the neutron magic number N = 8. We report our recent study about the possible relationship between the clustering and the breaking of the neutron magic number N = 20 in ³²Mg and ³⁰Ne. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: horiuchi@ruby.scphys.kyoto-u.ac.jp     

Quantitative analysis of alcohol-water binary solutions using Raman spectroscopy

Raman spectroscopy was used for rapid and in situ measurements of alcohols in alcohol-water binary systems. An external standard was used to eliminate factors such as laser power or instrumental effects. Band ratios between the Raman bands of the target molecule and that of acetonitrile as external standard were calculated and found to be proportional to the mass fraction of alcohol. Better linearity was achieved as compared with that in the calibration curve obtained by plotting the Raman intensity alone. The equations of the calibration curves were y=0.2747x with R² of 0.9996 and y=0.2189x+1.340×10⁻³ with an R² of 1.000 in methanol-water and in ethanol-water binary systems, with y and x denoting the Raman intensity ratio and the mass fraction of alcohol, respectively.     

Molecular relaxation behaviour of mixtures of some polar non-associative liquids

Molecular relaxation studies have been made on rigid polar solutes dibenzofuran and s-trioxane and their mixtures with benzophenone, ortho- and meta-dichlorobenzenes in the microwave region over a range of temperatures in dilute benzene solutions. The relaxation times and the thermodynamic parameters for the activated state have been determined using the measured dielectric data. The results obtained have been discussed in terms of the molecular motion of the system and are consistent with those of other rigid molecules studied previously. The results are also compared with the computed values obtained by employing a relation proposed by us earlier.     

Molecular origin of thermal diffusion in benzene + cyclohexane mixtures

The isotope effect in thermal diffusion (Soret effect) of benzene+cyclohexane mixtures has been investigated by a holographic grating technique. The Soret coefficient can be split into additive contributions. One contribution, the isotope effect, stems from the differences of both mass and moment of inertia, and is independent of composition. An additional "chemical" contribution depends on concentration and even changes its sign at a benzene mole fraction x(benz) approximately 0.7. The mass effect is in agreement with molecular dynamics calculations: the heavier component migrates to the cold side.     

Molecular relaxation of some rigid polar molecules and their mixtures

The dielectric behavior of benzene solutions of four rigid polar molecules, benzophenone, benzotrichloride, ortho- and meta- dichlorobenzenes and their mixtures has been studied in the microwave region over a range of temperatures. The dielectric data has been used to determine the relaxation times and the thermodynamic parameters for the activated state. The relaxation times for single component solutions agree well at temperatures at which literature values are available. The relaxation times for mixtures are consistent with those of other rigid molecules studied previously. The results have been also compared with the computed values obtained from a relation proposed by us.     

Molecular structure of graphite-polyimide interphases

The molecular orientation of adsorbed polyimides and model compounds with respect to highly oriented pyrolytic graphite (HOPG) surfaces was determined by reflection-absorption infrared (RAIR) spectroscopy. As the thickness of the pyromellitic diimide (PMDI) films decreased, bands near 766 and 729 cm^-1, which were assigned to the CNC out-of-plane bending modes, were relatively strong in the spectra, demonstrating that PMDI was adsorbed flat-down with the imide rings parallel to the HOPG surface. As the thickness of the N,N'-diphenylpyromellitic diimide (DPPMDI) films was decreased, bands near 1785 and 1722 cm^-1 which were assigned to the C=O stretching modes, were relatively strong in the RAIR spectra. Moreover, bands near 869, 841, 742, and 686 cm^-1 attributed to the out-of-plane bending modes of monosubstituted benzene rings became considerably stronger. It was suggested that the DPPMDI molecules nearest to the HOPG surface were adsorbed edge-on with the carbonyl groups perpendicular to the surface and with the monosubstituted benzene rings parallel to the surface. There were significant differences in relative band intensity observed between the transmission and RAIR spectra of polyimides derived from pyromellitic dianhydride (PMDA) and oxydianiline (ODA). The band near 1725 cm^-1 due to the C=O stretching mode increased its relative intensity in the RAIR spectra of PMDA/ODA polyimides, while the bands near 1499 and 1237 cm^-1 due to the ODA moieties decreased their relative intensities, implying that PMDA moieties were oriented edge-on with the carbonyl groups perpendicular to the surface and that the ODA moieties were oriented mostly parallel to the surface. However, the RAIR spectra obtained from PMDA and 2,2-bis[4-(4-aminophenoxy)-phenyl]-hexafluoropropane (4-BDAF) polyimides were similar to the transmission spectra of the polyimide, indicating that PMDA/4-BDAF was randomly oriented on the HOPG surface.     

Molecular structure of exotic mesons

The 0^— exotic meson state is considered as the P-wave molecular state ρ′(1465) of η(550) mesons. The mass and decay width of the exotic 0^— meson are calculated on the basis of the N/D dispersion method.     

Models of structure and properties of H-bonded molecular mixtures

Results on the modeling of molecular interactions, supramolecular organization and physicochemical properties of binary mixtures of organic solvents are presented. The mixtures, both with negative deviation from ideality, such as propanone–trichloromethane, dimethylsulfoxide–trichloromethane, and with positive deviation, such as 1,4-dioxane–methanol, 1,4-dioxane–ethanol, trichloromethane–methanol, trichloromethane–ethanol, have been studied. Models for the aggregation in mixtures due to specific intermolecular interactions are proposed. Integral and differential parameters of the supramolecular organization were obtained. Thermodynamic characteristics of aggregation (equilibrium constants, Gibbs energy, enthalpy and entropy) and structural parameters of the aggregates have been determined. Long-range molecular correlations and cooperativity of H-bonds have been established. The manifestations of the supramolecular ordering in the physicochemical properties of the mixtures are discussed.     

Ultrasoft colloid-polymer mixtures: structure and phase diagram

Binary mixtures of ultrasoft colloids and linear polymer chains were investigated by small-angle neutron scattering and liquid state theory. We show that experimental data can be described by employing recently developed effective interactions between the colloid and the polymer chains, in which both components are modeled as point particles in a coarse-grained approach, in which the monomers have been traced out. Quantitative, parameter-free agreement between experiment and theory for the pair correlations, the phase behavior and the concentration dependence of the interaction length is achieved.     

Molecular interaction and other thermodynamic properties in ternary liquid mixtures

Molecular interaction, adiabatic compressibility, intermolecular free length, molar volume, available volume and free volume have been computed by measuring ultrasonic velocity and density at 23°C in three ternary liquid mixtures with p-xylene as common component. The systems are I p-xylene-acetone-carbon tetrachloride, II p-xylene-acetone-cyclohexane and III p-xylene-benzene-cyclohexane. Molecular interaction is maximum when the mole fraction of acetone is 0.5 in I and 0.6 in II. It remains almost constant in III indicating no interaction in this case. The excess properties have also been given and the interactions explained.     

Molecular model for the VLE p- T-x relationships of binary mixtures

An analytical expression for the pressure-temperature-composition relations in the vapour - liquid equilibrium of non-polar binary mixtures is proposed. The model is based on a simple analytical expression for the vapour pressure of pure non-polar fluids, which, for a given temperature, requires as input only the Lennard- Jones molecular parameters and the acentric factor of the substance. The equilibrium mixture pressure is then expressed as a function of the vapour pressure of each component and of a mixture contribution. The molecular parameters required for this mixture contribution are related to the molecular parameters of the pure component through a modified Lorentz-Berthelot mixing rule, where the interaction parameters are given as simple functions of the temperature and composition, with eight appropriate constants for each binary mixture. We show that the model permits one to reproduce or predict in a simple way the pressure (for a given liquid mole fraction) or the liquid composition (for a given pressure).     

Survey of segregation alteration of hydrogen-helium mixtures via structure factor

In this study, thermodynamic instabilities in hydrogen-helium fluid mixture have been analyzed. These kinds of investigations are inevitable for indicating hydrodynamic transitions in Hydrogen-Helium fluid mixture. Therefore, first we have derived equation of state of mixture via Barker-Henderson statistical perturbation theory. Moreover, we have used Yiping radial distribution function in calculating perturbed terms. Via equation of state, we have calculated excess Gibbs free energy and the Gibbs free energy in the long wavelength limit. By means of this energy in hand we could estimate degree of hetero-coordination and segregations of this mixture which is a measure for defining thermodynamic instabilities. At last, these measurements have made us capable of anticipating thermodynamic instabilities and coordination of mixture in different concentrations.     

Positive ion structure in 3He-rich liquid helium mixtures

The structure of positive ions in impure ³He is investigated. We predict a “halo” of ⁴He around the ion. We use the halo to interpret recent experiments on ion mobility in ³He. Other properties of the halo are studied.