Journal of Molecular Liquids (v.150, #1-3)

Thermophysical properties of carbon nanotubes in toluene under high pressure by I. Adamenko; L. Bulavin; V. Korolovych; K. Moroz; Yu Prylutskyy (1-3).
It investigates the thermophysical properties and the equation of state of single-walled carbon nanotubes in liquid toluene. The equation of state is established for the investigated system. It analyzes the dependence of its constants on temperature and characteristics of the structure. Numerical values of isothermal elastic modulus are obtained as functions of pressure. It is found that the addition of carbon nanotubes in toluene caused the increase of the energy of molecular interaction in the investigated system.
Keywords: Carbon nanotubes; Thermophysical properties; Equation of state;

Dielectric properties of ammonium salt aqueous solutions by A. Lileev; A. Lyashchenko (4-8).
High-frequency dielectric permittivity, dielectric losses and low-frequency conductivity of aqueous solutions of ammonium salts (NH4NO3, NH4BF4, NH4C1O4, NH4SO3NH2, NH4HSO4, (NH4)2SO4, and NH4SCN) were measured at 288, 298 and 308 K. The parameters of the process of the dielectric relaxation (i.e. time τ and enthalpy of activation ΔHε ++) were calculated. These values characterize the mobility of water molecules in solutions. The structure-breaking effect is found for all investigated ammonium salts. The variation of this effect for different anions in dependence on factors determining the molecular-kinetic hydration of ions (form, size, charge, etc.) is established.
Keywords: Dielectric relaxation; Water; Solution; Electrolyte; Hydration;

The molar transition energy (E T) polarity values of 1-(p-dimethylaminophenyl)-2-nitroethylene were collected in mixed solvent systems comprising a formamide [N,N-dimethylformamide (DMF), N-methylformamide (NMF) and formamide (FA)] and a hydroxylic (water, methanol, ethanol, propan-1-ol, propan-2-ol, butan-1-ol, and 2-methylpropan-2-ol) solvent. Mixed systems containing DMF with the other formamides (NMF and FA) and NMF with FA were also studied. Each solvent system was analyzed in terms of both solute–solvent and solvent–solvent interactions. These latter interactions were responsible for the synergism observed in some mixtures. All data were successfully fitted to a model based on solvent exchange equilibria and the results suggest that both hydrogen bonding and solvophobic interactions contribute to the formation of the solvent complexes responsible for the observed synergistic effects in the PS of the dye.
Keywords: Preferential solvation; Amides; Binary mixtures; Mixed solvents;

Phase behavior of room temperature ionic liquid – H2O mixtures: N, N-diethyl-N-methyl-N-2-methoxyethyl ammonium tetrafluoroborate by Hiroshi Abe; Yukihiro Yoshimura; Yusuke Imai; Takefumi Goto; Hitoshi Matsumoto (16-21).
Phase behavior of room temperature ionic liquid (RTIL)-H2O mixtures (x  = 0.0-98.5 mol% H2O) was investigated by in-situ observations of simultaneous X-ray diffraction and differential scanning calorimetry method, and Raman spectroscopy: The RTIL is N, N-diethyl-N-methyl-N-2-methoxyethyl ammonium tetrafluoroborate, [DEME][BF4]. We found that the crystal structure at low temperature is almost the same as that of pure [DEME][BF4] over the whole range of water concentration. Above 60 mol%, H2O crystal appears inside the RTIL crystals. The difference in the enthalpy between the liquid and the solid state was estimated as a function of H2O concentration. In Raman spectra, a nearly-free hydrogen bonded band of H2O appears clearly below 90 mol%. We correlate the existence of nearly-free bonds in the [DEME][BF4]-H2O mixtures with the abrupt change of the enthalpy at around 90 mol%.
Keywords: Simultaneous X-ray diffraction and DSC measurements; Room temperature ionic liquids; Raman spectroscopy; Nearly-free hydrogen bonded water;

Dipole moment studies of complexes of alcohols with ethyl bromide by T. Indira; G. Parthipan; H. Aswathaman; T. Thenappan (22-24).
The experimental values of the dipolar increment of the complexes of ethyl bromide with p-cresol, cyclohexyl alcohol, butyl alcohol, and propyl alcohol in dilute solutions of benzene have been measured at a temperature of 308 K. Dipolar incremental values of the systems were calculated using Huyskens method based on Onsager′s theory. Some problems related to the dipole moment enhancement (Δμ) caused by hydrogen bond formation between donor and acceptor molecules are discussed.
Keywords: Dielectric constant; Density; Dipolar increment; Proton donor; Proton acceptor; Hydrogen bond;

The systems studied were water/sucrose laurate/ethoxylated mono-di-glyceride/isopropylmyristate/peppermint oil. The solubilization capacity of water in the oils is dependent on the surfactants and oils mixing ratios (w/w). The transport properties (electrical conductivity and dynamic viscosity) were studied as function of water volume fraction. Electric percolation phenomenon was observed in these systems and the water volume fraction percolation thresholds were determined. The diffusion properties investigated by nuclear magnetic resonance confirm a progressive transformation of the water-in-oil to bicontinuous and inversion to oil-in-water microemulsions that occur upon dilution with water. The diffusion coefficients of surfactants increase with the increase in the water volume fraction. The structural parameters studied by small angle X-ray scattering that include the periodicity and correlation length were estimated. The periodicity increases linearly with the increase in the water volume fraction whereas the correlation length increases with the increase in the water volume fraction to a certain value then decreases. Cryogenic transmission electron microscopy images for diluted microemulsions revealed the presence of spheroidal droplets of up to 10 nm diameter.
Keywords: Percolation threshold; Diffusion coefficients; Scattering intensity; Periodicity; Correlation length;

In the application of long range corrections to calculation of potential energy and pressure utilizing molecular dynamics simulation, it is common to use a longer distance of cut-off to obtain more accurate results. The radial distribution function is assumed to be equal to unity in conventional terms for the long range corrections. The main objective of this work is to introduce a methodology for obtaining a correlation for radial distribution function from preliminary simulation runs and then use it in other simulation runs with a smaller ratio of cut-off distance to collision diameter. This, in turn, results in much lower CPU time requirements. The radial distribution function is considered as a convergent oscillating function. A number of simulations were performed in NVT ensemble with the ratio of cut-off distance to collision diameter set to five. Also, two sets of simulations with the ratio of two were performed. The first set used the conventional term of long range corrections and the second used the term presented in this work. With the ratio of two, calculating the pressure of argon in liquid and supercritical fluid states resulted in much lower CPU time and less error. In predicting pressure, applying the new correlation for radial distribution function reduced the CPU time by a factor of twelve. Assuming cut-off distance to be twice the collision diameter also resulted in a decrease of nearly 4% in relative error. In addition, the effect of this modification on argon properties: such as heat capacity, thermal pressure coefficient and isothermal compressibility are investigated using molecular dynamics simulation data in fluctuation formulas.
Keywords: Molecular dynamics simulation; Long range corrections; Lennard–Jones; Argon; Thermodynamic properties;

Molar volume, viscosity and conductance of lithium chloride (LiCl), sodium chloride (NaCl) and potassium chloride (KCl) in 0.01 m aqueous ascorbic acid have been calculated from density, viscosity and conductance data at temperatures 303.15, 308.15, 313.15 and 318.15 K. The solute–solvent interactions for LiCl, NaCl and KCl have been inferred from ϕ v o, B-coefficient of Jones–Dole equation and Λ m o values. The structure making/breaking behavior of LiCl, NaCl and KCl is inferred from the sign of [∂2 ϕ v o/∂T2]p, dB/dT and temperature coefficient of Walden product i.e. d(Λ m o η o)/dT values. It has been found from molar volume, viscosity and conductance studies that LiCl, NaCl and KCl behaves as structure-breaker in 0.01 m aqueous ascorbic acid solution. The energy of activation for LiCl, NaCl and KCl is calculated from conductance and viscosity data and it has found that E Λ is less than E η .
Keywords: Molar volume; Viscosity; Conductance; Alkali chloride;

The ionic contribution to the dielectric susceptibility and to the impedance of a thin layer of dielectric liquid subjected to ac electric field was studied numerically. Quasi-blocking electrodes and equal mobility of anions and cations were assumed. Field dependent dissociation and recombination were taken into account. The polarization resulting from the ionic space charge was calculated. Its non-sinusoidal time dependence revealed the non-linear properties of the system. The linear and non-linear components of dielectric susceptibility were calculated as functions of frequency. The influence of the amplitude of bias voltage, layer thickness, concentration and mobility of ions was also studied. The frequency dependence of the real and imaginary parts of the electrical impedance revealed features characteristic for an equivalent circuit formed by the series of two parallels of a resistance and a capacitance. One of them may be attributed to the electrodes and the other to the bulk of the layer.
Keywords: Dielectric liquid; Impedance; Dielectric susceptibility;

The nature of solute–solvent interactions in ternary solutions of rifampicin–water–ethanol was investigated by means of electronic absorption spectra recorded in visible and in ultraviolet range respectively. Measurements upon the frequency in the absorption band maxima were carried out, the mathematical interpretation of the solvent spectral shifts, on the basis of Bakhshiev's theory, leading to the emphasizing of orientation and dynamic forces. Molecular orbital modeling applied by means of specialized soft, resulted in the computational approach of rifampicin dipole moment and intramolecular hydrogen bond lengths, evidencing also four metastable conformers.
Keywords: Rifampicin; Water–ethanol solutions; Solvent effect; Microscopic parameters;

2-Amino-4-methoxy-6-methyl-pyrimidine (AMMP) and 2-amino-4,6-dimethyl-pyrimidine (ADMP) react with 2,6-dichloro-4-nitrophenol (DCNP) to form yellow proton transfer (PT) complexes in acetonitrile at absorption maxima around 420 nm. These PT reactions have been applied to the simultaneous spectrophotometric determination of (AMMP) and (ADMP) in acetonitrile. Factors controlling the PT process were studied and optimized. Job's method of continuous variations was applied to identify the composition of the formed complexes. The PT complex formation constants (K PT) and the molar extinction coefficients (ε) were estimated using Benesi–Hildebrand equation. Moreover, the solid PT complexes were isolated and characterized using elemental analysis and infrared measurements.
Keywords: Pyrimidines; DCNP; Electronic spectra; PT complexes;

Clegg–Pitzer–Brimblecombe ion-interaction semi-empirical approach was rarely exploited for modeling electrolyte, particularly, in mixed solvent systems. Indeed, a review of the literature shows that the use of an exact and complete form of this model (PSC) was only limited to the works of two research groups for the investigation of electrolyte in mixed solvent systems. In this work, we have used both Pitzer and PSC ion-interaction theoretical approaches for modeling the non-ideal behavior of HCl in the ternary HCl + methanol + water electrolyte system. The modeling purposes were achieved based on the experimental determination of the mean molal activity coefficients for HCl in this ternary system by using the potentiometric data of a galvanic cell containing a pH glass membrane and Ag/AgCl electrodes. The measurements were performed over the electrolyte molality ranging from 0.01 up to 5.75 mol/kg in mixed methanol (x%) + water (100 −  x%) solvent, with solvent mass fraction percents: x% = 10, 20, 30, 40 and 50%, at 298.15 ± 0.05 K.
Keywords: Activity coefficient; Pitzer; Pitzer–Simonson–Clegg; Mixed solvent;

We present molecular dynamics simulations of the seventeen-atom system of chloroform equimolar in benzene on the basis of a previously proven Fortran code, Lennard–Jones potential parameters, fractional atomic charges, and complete molecular structure data between 248 and 498 K at a common density. Specifically, the generated l  = 1 orientational auto-correlation functions of the tumbling and spinning–tumbling motions of chloroform in its benzene solution are combined, by established group-theoretical principles, to three linear combinations that quantitatively characterize for the benzene-dissolved chloroform molecules the time evolution of the average direction of their average rotation axis as well as that of the mean rotation angle around it. Based on these findings we conclude, first, that the probability density function of the average rotational motion of the dissolved chloroform molecules follows a memory-less process (Markoffian), second, that a previously proposed 1:1 chloroform–benzene complex, with the H atom of the C–H bond of its chloroform moiety pointing to the center of the plane of an adjacent benzene species, has a near-vanishing probability to prevail in the solution.
Keywords: Molecular dynamics simulation; Search for equimolar chloroform–benzene complex; Orientational correlation functions; Average direction of average rotation axis; Mean rotation angle; Molecular shape; Rotational Markoff process;

Densities, speeds of sound and refractive indices for the binary mixture of dibutyl ether and 1-chlorobutane have been determined at atmospheric pressure and at the temperature range from 283.15 K to 313.15 K. Excess volumes, excess isentropic compressibilities and refractive index deviations have been calculated from the experimental data and fitted by the Redlich–Kister equation. Excess volumes and isentropic compressibilities are negative over the whole composition range while refractive index deviations are positive.
Keywords: Thermodynamic properties; Densities, speeds of sound; Refractive indices; Dibutyl ether; 1-Chlorobutane;

This work presents a phenomenological theory for the single-chain dynamics in semidilute and concentrated polymer solutions and allows to describe the crossover from Zimm to Rouse-like behavior both in time domain and in spatial domain. The polymer solution is described as a set of oscillators fixed in space and submerged in an incompressible fluid. It is shown that the coupled equations of motion of such a polymer system give rise to the time dependence of the Oseen-like tensor and, as a consequence, the time-dependent hydrodynamic screening length. Monomer mean-square displacements and the single-chain dynamic structure factor are calculated.
Keywords: Polymer solution; Hydrodynamic screening;

To test the validity of existing scaling laws which express the possible relationship between the excess entropy and transport properties, the diffusion and viscosity coefficients of liquid Fe, Co and Ni metals are calculated. To predict excess entropy, the pair distribution functions are calculated from the solution of Ornstein–Zernike integral equation. It is shown that the scaling laws proposed by Dzugutov for diffusion and by Li et al. for viscosity lead to a good estimation for diffusion and viscosity coefficients at the melting point.
Keywords: Liquid metals; Transport properties; Scaling law; Surface tension;

The interaction between nonionic semi-flexible polymer, hydroxypropylcellulose (HPC) and cationic surfactant hexadecylbenzyldimethylammonium chloride (C16BzCl) has been studied in aqueous sodium chloride (NaCl), sodium hexanoate (NaHx) and propylammonium chloride (PrACl) solutions employing conductivity, viscosity and cloud point measurements. The salts selected allowed us to investigate the effect of hydrophobic co- and counter-ions compared with simple ions upon polymer–surfactant interaction. Cloud point and viscometric results indicate interaction between C16BzCl and HPC although not reflected from condutometric data. Addition of different levels of salts to the polymer–surfactant system reveal that the charge compensation of micelles bound to the polymer chains is less in the presence of NaHx than in NaCl or PrACl, both showing similar effect. Also the effect of increase in surfactant concentration at a particular polymer plus additive concentration is equivalent to the increase in hydrophobic modification of the polymer as reflected in cloud point and viscosity decrease.
Keywords: Hyrdoxypropyl cellulose; Polymer–surfactant interaction; Hydrophobic salts; Cloud point;