A new correlation on predicting self- and mutual-diffusion coefficient of Lennard–Jones chain fluid

The Stokes–Einstein (SE) equation is often applied as an approximation of self-diffusion coefficients D of molecular species based on the shear viscosity of fluids. The SE relation gives rough estimates of self-diffusion coefficients in liquid states and (divergently) high deviations for the gaseous phase. Inspired by Rosenfeld’s entropy scaling approach, we find a universal function of residual entropy f(s res) to describe the ratio between experimental and calculated D from SE equation for all investigated substances. The so-obtained modified SE equation, containing 5 universal parameters adjusted to experimental data of 61 substances of 11 different chemical families, can be used for predicting D in the entire fluid region, with averaged absolute deviations of 12.3% compared to experimental data (5407 data points). The application of the proposed model to diffusion coefficients at infinite dilution shows average deviations of 20.8% for widely different systems (412 data points).

Section: Introductionmentioning

confidence: 99%

Modified Stokes–Einstein Equation for Molecular Self-Diffusion Based on Entropy Scaling

Zmpitas

Groß

2021

“…Due to the constant need for reliable estimation of diffusivities, modeling and correlation of diffusion data have long been a subject of immense research interest. Currently, publications found in this area of study are considerable in the literature. − There is clearly still a strong demand for good models and general equations that can be applied to accurately correlate or predict diffusivities of solute compounds in solutions, especially those that are applicable for a broad range of solvents and temperatures.…”

Section: Introductionmentioning

confidence: 99%

Diffusivities of Aromatic Compounds: A New Molecular-Hydrodynamic Model for Nonassociated Pseudoplanar Solutes at Infinite Dilution

Chan

Chang

et al. 2019

Diffusivities of nonassociated aromatic compounds at infinite dilution in methanol and in cyclohexane were measured by the Taylor dispersion method. At constant temperatures, the diffusivity reciprocals of the pseudoplanar solutes in either solvent showed a linear dependence on the molecular volumes of the solutes. The activation energies of solute diffusion were determined, and the results for each solvent indicated that such energies are fairly insensitive to the size and mass of the disc-shaped solutes ranging from benzene to hexamethylbenzene. The effects of temperature, solute size, and solvent properties on diffusivity were further found to be accurately described by a new molecular-modified fractional Stokes–Einstein relation. Employing additional literature diffusivities for the same type of solutes, a general fractional molecular-hydrodynamic equation with only two constants has been established to predict 326 limiting mutual diffusivities that cover a broad range of solutes, solvents, and temperatures to an average absolute deviation of 2.61% only.

“…The approach was originally derived for n -alkanes and was expanded to other groups of substances and to mixtures. Other methods are based on the rough hard sphere theory, such as the effective hard sphere diameter method, − or methods using simultaneous free-volume modeling. , Of course, molecular simulations − can be used to determine transport properties, such as self-diffusion.…”

Section: Introductionmentioning

confidence: 99%

Self-Diffusion Coefficients from Entropy Scaling Using the PCP-SAFT Equation of State

Hopp

Mele

Groß

2018

This study proposes a model for self-diffusion coefficients of pure substances from entropy scaling using the perturbed-chain polar statistical associating fluid theory (PCP-SAFT) equation of state. In accordance with the entropy scaling approach proposed by Y. Rosenfeld [RosenfeldY. Rosenfeld, Y. Phys. Rev. A1977152545–2549], we observe that the self-diffusion coefficient of real substances, once made dimensionless with an appropriate expression, only depends on residual entropy. The proposed model requires 3 parameters for each pure substance. For substances with scarce experimental data, however, a scheme is proposed to estimate one or two of these parameters. We study 133 substances from more than 14 different chemical families and find the average absolute deviation of 8.2% between the proposed model and experimental data (9992 data points). The model shows satisfying robustness for extrapolating self-diffusion coefficients to conditions rather distant from the state points where experimental data are available.