Relations between transport coefficients and their density and temperature dependence

Nonequilibrium statistical mechanics via density fluctuation theory predicts relations between the bulk and shear viscosity, thermal conductivity, and self-diffusion coefficient of a fluid. In this Feature Article, we discuss such relations holding for fluids over wide ranges of density and temperature experimentally studied in the laboratory. It is discussed how such relations can be used to successfully compute the density and temperature dependence on the basis of intermolecular interaction potential models with the help of the modified free volume theory and the generic van der Waals equation of state once the parameters in them are determined at a low density or at a subcritical temperature. Although some approximations have been made to derive them, they represent a reliable molecular theory of transport coefficients over the entire density and temperature ranges of fluids--namely, gases and liquids--a theory hitherto unavailable in the kinetic theory of liquids and dense gases.     

General expression for the density dependence of the mori coefficients

The particular expression that relates the first Mori coefficients of the solvent particles with the solute particles as a function of their masses m₁ and m₂ is generalized to the case of the solute particle also having a different volume. The resulting density relationship, in terms of the mass factor M(m₂) and coupling constants C_D, is also valid for the second Mori coefficients and for two- and three-dimensional system. © 1992 by John Wiley & Sons, Inc.     

A simple method for calculation of the surface tension of molecular inorganic liquids

A method was proposed for calculation of the temperature dependence of the surface tension using a single experimental characteristic of a substance, its boiling point.     

Molecular friction coefficients in polymers and their temperature dependence

Colloid and Polymer Science - Analysis of the temperature dependence of viscoelastic and dielectric relaxation processes in several individual polymers by the equation of Williams, Landel, and...     

The temperature dependence of the surface tension of monatomic liquids and the boiling transition

We have reviewed recent model theories of the surface tension and examined the data on the temperature dependence of the surface tension of elemental liquids. From this, we have been able to show that the surface tension of these liquids vary linearly with temperature with the linear coefficient being related to both the transition temperatures at melting and at boiling. We use this to show that the boiling transition temperature may be expressed in a form which was previously proposed by us in a general phenomenological theory of phase transitions involving quasi-particles.     

The temperature dependence of the electron mobility in molecular crystals

We show that a hopping model may explain the experimental temperature dependence of the electron mobility in molecular crystals. The flat, higher temperature portion is obtained if anharmonic effects are included in a simple manner. The low temperature part is obtained if coherent effects are added to the diffusional ones.     

Ion diffusion coefficients through polyelectrolyte multilayers: temperature and charge dependence

The diffusion coefficient is a fundamental parameter for devices exploiting the ion transport properties of polyelectrolyte multilayers (PEMUs) and complexes. Here, the transport of ferricyanide through a multilayer made from poly(diallyldimethylammonium chloride) (PDADMA) and polystyrene sulfonate (PSS) was studied as a function of temperature or salt concentration. Accurate and precise measurements of ion diffusion coefficients were obtained using steady-state electrochemistry to determine the flux and Fourier transform infrared (FTIR) spectroscopy to measure the PEMU concentration. It was found that the concentration of ferricyanide inside the film decreased with temperature. Membrane transport is strongly thermally activated with activation energy 98 kJ mol(-1). A potential shift with decreasing salt concentration in cyclic voltammograms was translated into a differential flux caused by significantly higher diffusion coefficients for ferricyanide as compared to ferrocyanide.     

Equations of state for fluids: empirical temperature dependence of the second virial coefficients

In this paper, an empirical dependence of the second virial coefficients is derived from equations of state. The second virial coefficient B2 is found to be a linear function of 1/T1+beta, where T is the temperature and beta is a constant and has different value for different substances. Excellent experimental supports to this relationship are reported for nonpolar fluids, polar fluids, heavy globular molecule fluids, and quantum fluid He-4.     

An interference refractometer to measure the pressure and temperature dependence of the refractive index of liquids

The design of an interference refractometer, using laser radiation, to determine the pressure and temperature variation of refractive index is reported. The method does not attempt to determine the absolute refractive indices. The performance of the refractometer was tested using water and methanol. The results for a series of solutions of KBr in water are also reported and the results are compared with previous empirical estimates.     

Inverse temperature dependence of strain hardening in ultrahigh molecular weight polyethylene: role of lamellar coupling and entanglement density

Irradiation of ultrahigh molecular weight polyethylene (UHMWPE) with a dose of 150 kGy by an electron beam can effectively increase the entanglement density in the amorphous phase and has little influence on the properties of the crystalline phase, which provides examples to comparatively investigate the role of lamellar coupling and entanglement density in determining the strain-hardening effect in semicrystalline polymers. The strain-hardening modulus, deduced from the Haward plots of true stress-strain curves, is inversely temperature-dependent and has a sharp transition around 65 degrees C that corresponds to the mechanical alphaI-process of the crystalline phase for both nonirradiated and irradiated samples, irrespective of the entanglement density in the amorphous phase. Lamellar coupling takes more effect in determining the strain-hardening behavior before the mechanical alphaI-process is activated. With further increasing temperature, lamellar coupling becomes weaker and the role of the entangled amorphous phase is gradually presented. However, the same temperature dependence of the strain-hardening modulus in both nonirradiated and irradiated samples indicates that the strain-hardening behavior in semicrystalline polymer is mostly determined by lamellar coupling rather than by entanglement density.     

Calculation of temperature dependence of radon emanation due to alpha recoil

Many experimental and modeling studies have examined several factors affecting radon emanation. Of these factors, the effect of temperature shown in earlier experiments has not been discussed with model calculations. In the present study, radon emanation fractions were calculated for various temperatures, namely different air densities, using a simple model into which the emanation processes originating from alpha recoil were incorporated. As a result, the slightly negative correlation that the radon emanation fraction decreased with increasing temperature was observed within a certain range of grain size, while temperature had no effect within the other range. Considering the current knowledge of processes through which radon emanation occurs, this result would be expected to be qualitatively reasonable. However, the result is not similar to all previous experimental results showing the positive correlation. These papers occasionally explain that the positive correlation is attributable to the adsorption of radon on solids during its transfer among grains. Since the general definition of radon emanation includes no transfer process after its release from a grain, their explanation could not be well established. The discrepancy between the calculated and measured data may suggest the needs of review and improvement of experimental and/or modeling techniques.     

Predicting the preexponential temperature dependence of bimolecular metathesis reaction rate coefficients using transition state theory

The thermochemical kinetics formulation of conventional transition state theory for bimolecular reactions allows for a separate contribution from each degree of freedom (translation, rotation, vibration, etc.) in the activated complex to the entropy and heat capacity of activation, and thus to the preexponential terms in the Arrhenius rate expression, k = ATⁿ exp(?B/T). The number of vibrations and (possibly hindred) internal rotations varies depending on the nature of the reaction: atom + diatom, diatom + linear polyatom, etc. The temperature exponent n can be evaluated explicitly for each type of reaction if the harmonic oscillator-rigid free rotor approximation is valid for the reagents and activated complex and if the contribution from tunneling is small. Various reaction types are examined successively, and n is evaluated for each case. The possible contributions of other factors (vibrational anharmonicity, hindered internal rotation, tunneling, “looseness” of activated complex) to the value of n are also considered.     

Composition and temperature dependence of cesium-borate glasses by molecular dynamics

The structural aspects of xCs2O-(1-x)B2O3 glasses have been investigated by molecular dynamics as functions of Cs2O content (x=0.2, 0.3, and 0.4) and temperature (T=300 and 1250 K). The tetrahedral (B?4-) and triangular (B?3,B?2O-, and B?O2 (2-)) short-range order borate units were found to be the structure-building entities of the simulated glasses [?=bridging oxygen (BO) and O-=nonbridging oxygen (NBO) atom]. The increase of Cs2O content results in the progressive increase of the NBO-containing triangle population at the expense of the BO4- tetrahedral units. The same effect is caused by temperature increase at a fixed Cs2O content, and this was associated with the "fragile" characteristics of alkali borate glasses. A comparison of simulated Cs and Li borates showed very similar structures at x=0.2, but dissimilar ones when the alkali content exceeds this composition. In particular, for x>0.2 Cs borates exhibit a preference for NBO formation relative to Li borates. Differences in the microstructure of sites hosting Cs ions were found, and this permits their classification into bridging (b type) and nonbridging type (nb type) of sites. b-type sites consist exclusively of BO atoms, while both BO and NBO atoms participate in nb-type sites. These differences in Cs-site local bonding characteristics were found to be reflected on the Cs-O(site) vibration frequencies. Also, the computed Cs-O vibrational responses for simulated Cs borates were found to compare well with experimental far-infrared spectra.     

Room temperature ionic liquids containing low water concentrations-a molecular dynamics study

We have performed classical molecular dynamics to study the properties of a water-miscible and a water-immiscible room-temperature ionic liquid when mixed with small quantities of water. The two ionic liquids consist of the same 1-ethyl-3-methylimidazolium ([EMIM]) cation combined with either the boron tetrafluoride ([BF(4)]) or bis(trifluoromethylsulfonyl)imide ([NTf(2)]) anion. It is found that, in both ionic liquids, water clusters of varying sizes are typically hydrogen bonded to two anions with the cation playing a minor role. We also highlight the difficulties of obtaining dynamic quantities such as self-diffusion coefficients from simulations of such viscous systems.     

On the density scaling of pVT data and transport properties for molecular and ionic liquids

In this work, a general equation of state (EOS) recently derived by Grzybowski et al. [Phys. Rev. E 83, 041505 (2011)] is applied to 51 molecular and ionic liquids in order to perform density scaling of pVT data employing the scaling exponent γ(EOS). It is found that the scaling is excellent in most cases examined. γ(EOS) values range from 6.1 for ammonia to 13.3 for the ionic liquid [C(4)C(1)im][BF(4)]. These γ(EOS) values are compared with results recently reported by us [E. R. López, A. S. Pensado, M. J. P. Comu?as, A. A. H. Pádua, J. Fernández, and K. R. Harris, J. Chem. Phys. 134, 144507 (2011)] for the scaling exponent γ obtained for several different transport properties, namely, the viscosity, self-diffusion coefficient, and electrical conductivity. For the majority of the compounds examined, γ(EOS) > γ, but for hexane, heptane, octane, cyclopentane, cyclohexane, CCl(4), dimethyl carbonate, m-xylene, and decalin, γ(EOS) < γ. In addition, we find that the γ(EOS) values are very much higher than those of γ for alcohols, pentaerythritol esters, and ionic liquids. For viscosities and the self-diffusion coefficient-temperature ratio, we have tested the relation linking EOS and dynamic scaling parameters, proposed by Paluch et al. [J. Phys. Chem. Lett. 1, 987-992 (2010)] and Grzybowski et al. [J. Chem. Phys. 133, 161101 (2010); Phys. Rev. E 82, 013501 (2010)], that is, γ = (γ(EOS)/φ) + γ(G), where φ is the stretching parameter of the modified Avramov relation for the density scaling of a transport property, and γ(G) is the Gru?neisen constant. This relationship is based on data for structural relaxation times near the glass transition temperature for seven molecular liquids, including glass formers, and a single ionic liquid. For all the compounds examined in our much larger database the ratio (γ(EOS)/φ) is actually higher than γ, with the only exceptions of propylene carbonate and 1-methylnaphthalene. Therefore, it seems the relation proposed by Paluch et al. applies only in certain cases, and is really not generally applicable to liquid transport properties such as viscosities, self-diffusion coefficients or electrical conductivities when examined over broad ranges of temperature and pressure.