Diffusivities in Binary Mixtures of Cyclohexane or Ethyl Butanoate with Dissolved CH₄ or R143a Close to Infinite Dilution

Abstract

This work is part of a series of studies focusing on binary mixtures consisting of a liquid with a dissolved gas close to infinite dilution. A particular focus is on the study of the influence of molecular characteristics on mutual or self-diffusivity. Heterodyne dynamic light scattering (DLS) experiments and equilibrium molecular dynamics (EMD) simulations are applied to determine the Fick diffusion coefficient D 11 and the self-diffusion coefficient of the gas solute in the mixture D self,1 . Often, the latter is referred to in the literature as the intradiffusion coefficient, which is equal to D 11 in the limit of infinite dilution. Both DLS and EMD simulations are applied in macroscopic thermodynamic equilibrium at or close to saturation conditions. In the present study, mixtures of methane (CH 4 ) or the refrigerant 1,1,1-trifluoroethane (R143a) dissolved in cyclohexane or ethyl butanoate are investigated at temperatures T between 303 and 423 K. The average expanded experimental uncertainty (coverage factor k = 2) of D 11 from DLS experiments is 10%, and the average expanded statistical uncertainty (k = 2) of D self,1 from EMD simulations is 6.4%. Unexpectedly, D 11 in mixtures of CH 4 dissolved in cyclohexane or ethyl butanoate essentially matches within uncertainties at a given T, and mixtures of cyclohexane with R143a show smaller D 11 values in comparison to ethyl butanoate with R143a.

Mutual and Thermal Diffusivities in Binary Mixtures of n-Hexane or 1-Hexanol with Krypton, R143a, or Sulfur Hexafluoride by Using Dynamic Light Scattering and Molecular Dynamics Simulations

“…In the experiment, Θ s is determined via Snell–Descartes law using n fluid and the incident angle Θ i defined by the direction of observation and that of the incident light. Examples of experimental CFs obtained in binary systems consisting of liquids with dissolved gases are shown, for instance, in refs , and . In line with previous studies, the final D 11 and a data at a given thermodynamic state represent weighted averages of at least 12 independent experimental CFs obtained for at least six different scattering geometries with two types of hardware correlators.…”

“…In agreement with previous studies, − , the solvents n -C 6 H 14 and 1-C 6 H 14 O are modeled with the L-OPLS-T FF, which is an extended version of the all-atom Optimized Potentials for Liquid Simulations (OPLS) , FF for long-chain hydrocarbons (L-) , with a T -dependent modification proposed by Klein et al (- T ) applied. The dissolved gas R143a is modeled with OPLS parameters , without the T -dependent modification applied.…”

“…Coulombic and Lennard-Jones (LJ) interactions are calculated within a cutoff radius of 1.6 nm and approximated with the Particle-Mesh-Ewald , algorithm and standard dispersion corrections beyond this limit. The system is equilibrated at the desired T and p in the same manner as described in our previous publication using the v -rescale and c -rescale algorithms provided within the GROMACS software . Typical simulation runtimes are around 50 ns.…”

Diffusivities in Binary Mixtures of Ammonia Dissolved in n-Hexane, 1-Hexanol, or Cyclohexane Determined by Dynamic Light Scattering and Molecular Dynamics Simulations

“…All simulations in this work are performed using the GROMACS software package version 2021.1 . Simulation details are identical to recent works. ,, In particular, the reader is referred to ref . The simulations were initiated by randomly placing the solute and solvent molecules in a cubic simulation box with an edge length of 5.9–7.6 nm and periodic boundary conditions in all directions.…”

“…η L is required as input to correct for finite-size effects in the diffusivities . Further details regarding the calculation of η L , D self , Γ 11 , Đ 12 , and D 11 from EMD simulations are outlined in our previous work. − ,,, The simulation runtime is approximately 40–60 ns total with a 1 fs timestep and no bond constraints. The saving frequency for interaction potentials and atom positions are 3 fs and 1 ps.…”