Application of rough hard-sphere theory to diffusion in n-alkanes (original) (raw)
Theory and Experiment of Binary Diffusion Coefficient of n-Alkanes in Dilute Gases
The journal of physical chemistry. A, 2016
Binary diffusion coefficients were measured for n-pentane, n-hexane, and n-octane in helium and of n-pentane in nitrogen over the temperature range of 300 to 600 K, using reversed-flow gas chromatography. A generalized, analytical theory is proposed for the binary diffusion coefficients of long-chain molecules in simple diluent gases, taking advantage of a recently developed gas-kinetic theory of the transport properties of nanoslender bodies in dilute free-molecular flows. The theory addresses the long-standing question about the applicability of the Chapman-Enskog theory in describing the transport properties of nonspherical molecular structures, or equivalently, the use of isotropic potentials of interaction for a roughly cylindrical molecular structure such as large normal alkanes. An approximate potential energy function is proposed for the intermolecular interaction of long-chain n-alkane with typical bath gases. Using this potential and the analytical theory for nanoslender b...
Experiments on tracer diffusion in aqueous and non-aqueous solvent combinations
The Journal of chemical physics, 2014
Forced Rayleigh scattering is used to study the tracer diffusion of an azobenzene in binary combinations of polar solvents, including water. In the absence of water, the tracer diffusion coefficient D in the mixture lies between the diffusion coefficients within the pure solvents, on a curve that is reasonably close to the prediction of free-volume theory. If water is present, on the other hand, the diffusion coefficient displays a minimum that is less than the smaller of the two pure-solvent values. We attempt to understand the different behavior in water by concentrating on the fairly hydrophobic nature of the solute, leading to a first solvent shell that is hydrophobic on the inside and hydrophilic on the outside. We also believe that clusters of amphiphiles explain the observation that, in aqueous combinations, D is nearly constant above a certain amphiphile mole fraction.
Modelling the Diffusion Coefficients of Dilute Gaseous Solutes in Hydrocarbon Liquids
International Journal of Thermophysics, 2021
In this work, we present a model, based on rough hard-sphere theory, for the tracer diffusion coefficients of gaseous solutes in non-polar liquids. This work extends an earlier model developed specifically for carbon dioxide in hydrocarbon liquids and establishes a general correlation for gaseous solutes in non-polar liquids. The solutes considered were light hydrocarbons, carbon dioxide, nitrogen and argon, while the solvents were all hydrocarbon liquids. Application of the model requires knowledge of the temperature-dependent molar core volumes of the solute and solvent, which can be determined from pure-component viscosity data, and a temperature-independent roughness factor which can be determined from a single diffusion coefficient measurement in the system of interest. The new model was found to correlate the experimental data with an average absolute relative deviation of 2.7 %. The model also successfully represents computer-simulation data for tracer diffusion coefficients ...
Mutual diffusion coefficients for two n-octane isomers in n-heptane
International Journal of Thermophysics, 1989
A new instrument for the measurement of mutual diffusion coefficients in the liquid phase based on the Taylor dispersion technique has been developed. The instrument design and operation are described. The working region of the instrument has been established using an ideal model for the apparatus. The necessary design considerations and corrections to ensure that the instrument operates in accordance with the theory of the method are discussed. The accuracy of the experimental results is estimated to be + 1%. Experimental data for n-octane and 2,2,4-trimethylpentane at infinite dilution in n-heptane are reported. Correlation schemes based on the rough-hard sphere theory have been used to represent the experimental data and their predictive capability examined.
The Journal of Chemical Physics, 2005
We present results of theoretical study and numerical calculation of the dynamics of molecular liquids based on combination of the memory equation formalism and the reference interaction site model -RISM. Memory equations for the site-site intermediate scattering functions are studied in the mode-coupling approximation for the first order memory kernels, while equilibrium properties such as site-site static structure factors are deduced from RISM. The results include the temperature-density(pressure) dependence of translational diffusion coefficients D and orientational relaxation times τ for acetonitrile in water, methanol in water and methanol in acetonitrile, all in the limit of infinite dilution. Calculations are performed over the range of temperatures and densities employing the SPC/E model for water and optimized site-site potentials for acetonitrile and methanol. The theory is able to reproduce qualitatively all main features of temperature and density dependences of D and τ observed in real and computer experiments. In particular, anomalous behavior, i.e. the increase in mobility with density, is observed for D and τ of methanol in water, while acetonitrile in water and methanol in acetonitrile do not show deviations from the ordinary behavior. The variety exhibited by the different solute-solvent systems in the density dependence of the mobility is interpreted in terms of the two competing origins of friction, which interplay with each other as density increases: the collisional and dielectric frictions which, respectively, increase and decrease with increasing density.
Atomistic molecular dynamics simulation of diffusion in binary liquid n-alkane mixtures
Well relaxed atomistic configurations of binary liquid mixtures of n-alkanes, obtained via a new Monte Carlo simulation algorithm ͓Zervopoulou et al., J. Chem. Phys. 115, 2860 ͑2001͔͒, have been subjected to detailed molecular dynamics simulations in the canonical ensemble. Four different binary systems have been simulated ͑C 5 -C 78 at Tϭ474 K, C 10 -C 78 at Tϭ458 K, and C 12 -C 60 at Tϭ403.5 and 473.5 K͒. Results are presented for the diffusion properties of these mixtures over a range of concentrations of the solvent ͑lighter component͒. The self-diffusion coefficients of the n-alkanes, calculated directly from the simulations, are reported and compared with the predictions of two theories: the detailed free volume theory proposed by Vrentas and Duda based on the availability of free volume in the blends, and a combined Rouse diffusant and chain-end free volume theory proposed by Bueche and von Meerwall et al. A direct comparison with recently obtained experimental data ͓von Meerwall et al., J. Chem. Phys. 111, 750 ͑1999͔͒ is also presented.
Mutual diffusion coefficients of heptane isomers in nitrogen: A molecular dynamics study
The Journal of Chemical Physics, 2011
The accurate knowledge of transport properties of pure and mixture fluids is essential for the design of various chemical and mechanical systems that include fluxes of mass, momentum, and energy. In this study we determine the mutual diffusion coefficients of mixtures composed of heptane isomers and nitrogen using molecular dynamics (MD) simulations with fully atomistic intermolecular potential parameters, in conjunction with the Green-Kubo formula. The computed results were compared with the values obtained using the Chapman-Enskog (C-E) equation with Lennard-Jones (LJ) potential parameters derived from the correlations of state values: MD simulations predict a maximum difference of 6% among isomers while the C-E equation presents that of 3% in the mutual diffusion coefficients in the temperature range 500-1000 K. The comparison of two approaches implies that the corresponding state principle can be applied to the models, which are only weakly affected by the anisotropy of the interaction potentials and the large uncertainty will be included in its application for complex polyatomic molecules. The MD simulations successfully address the pure effects of molecular structure among isomers on mutual diffusion coefficients by revealing that the differences of the total mutual diffusion coefficients for the six mixtures are caused mainly by heptane isomers. The cross interaction potential parameters, collision diameter σ 12 , and potential energy well depth ε 12 of heptane isomers and nitrogen mixtures were also computed from the mutual diffusion coefficients.
Journal of Physical Chemistry B, 1998
An understanding of the effect of specific solute-solvent interactions on the diffusion of a solute probe is a long standing problem of physical chemistry. In this paper a microscopic treatment of this effect is presented. The theory takes into account the modification of the solvent structure around the solute due to this specific interaction between them. It is found that for strong, attractive interaction, there is an enhanced coupling between the solute and the solvent dynamic modes (in particular, the density mode), which leads to a significant increase in the friction on the solute. The diffusion coefficient of the solute is found to depend strongly and nonlinearly on the magnitude of the attractive interaction. An interesting observation is that specific solutesolvent interaction can induce a crossover from a sliplike to a sticklike diffusion. In the limit of strong attractive interaction, we recover a dynamic version of the solvent-berg picture. On the other hand, for repulsive interaction, the diffusion coefficient of the solute increases. These results are in qualitative agreement with recent experimental observations.
Molecular dynamics study of diffusion of heavy water in normal water at different temperatures
Journal of Molecular Liquids
In the present work we study the diffusion of heavy water in the ordinary water and their mutual diffusion coefficient. Molecular dynamics studies of a binary mixture of heavy water (SPC/HW) and ordinary water (SPC/E), at heavy water mole fraction of 0.024 have been done at different temperatures ranging from 295 K to 318 K. Oxygen–oxygen radial distribution functions (RDF) have been evaluated. Self-diffusion coefficients of both solvent and solute have been determined by means of mean-squared displacement (MSD) versus time curves using Einstein's diffusion relation. Darken's relation has been used for determining the mutual diffusion coefficients at the respective temperatures. The variation of the diffusion coefficients along with temperature has been analyzed. Our results agree very well with the available previously reported experimental data.