Hard-wall Potential Function for Transport Properties of Alkali Metals Vapor

This study demonstrates that the transport properties of alkali metals are determined principally by the repulsive wall of the pair interaction potential function. The (hard-wall) Lennard-Jones(15-6) effective pair potential function is used to calculate transport collision integrals. Accordingly, reduced collision integrals of K, Rb, and Cs metal vapors are obtained from Chapman-Enskog solution of the Boltzman equation. The law of corresponding states based on the experimental-transport reduced collision integral is used to verify the validity of a LJ(15-6) hybrid potential in describing the transport properties. LJ(8.5-4) potential function and a simple thermodynamic argument with the input PVT data of liquid metals provide the required molecular potential parameters. Values of the predicted viscosity of monatomic alkali metals vapor are in agreement with typical experimental data with the average absolute deviation 2.97% for K in the range 700-1500 K, 1.69% for Rb, and 1.75% for Cs in the range 700-2000 K. In the same way, the values of predicted thermal conductivity are in agreement with experiment within 2.78%, 3.25%, and 3.63% for K, Rb, and Cs, respectively. The LJ(15-6) hybrid potential with a hard-wall repulsion character conclusively predicts best transport properties of the three alkali metals vapor.Comment: 21 pages, 5 figures, 41 reference

Simulation Investigation of Bulk and Surface Properties of Liquid Benzonitrile: Ring Stacking Assessment and Deconvolution

This manuscript is devoted to classical molecular dynamics (MD) simulation studies of the bulk and surface properties of liquid benzonitrile (BZN) in the temperature range of 293-323K. The content and the simulation-analysis are inspired by our recent ab initio calculation on benzonitrile, whereas present results are to expand and develop macroscopic documentation involving data verification. We investigate the molecular stacking that involves phenyl ring, which is notably absent in the counterpart acetonitrile solvent. MD simulations of the bulk liquid unravel the hydrogen bond (C≡N⋯H) formation and strength, in the order of ortho-H >> meta-H ~>para-H. The possibility for ortho-H’s to get involved in the formation of two bonds simultaneously confirms each having - and -bonding features. The singularity centered at about 313 K found in the trend of the simulated temperature-dependent viscosity and diffusion coefficient of liquid BZN goes alongside the reported experiment, and the phenomenon may root from a change in the internal frictional motion of the molecular cluster in stacking modes. Accordingly, we used vast efforts for analysis particularly based on the deconvolution of the corresponding complex correlation functions. Specific angle-dependent correlation functions led to the recognition of the stacking molecules and their strict orientational character by utilizing relative molecular twist angles. Recognition of the strict orientational character of the stacking molecules, as a clue to the singularity in the viscosity trend, will be discussed based on specific angle-dependent correlation functions

Adsorption and Orientation of Ionic Liquids and Ionic Surfactants at Heptane/Water Interface

Molecular dynamics simulation of heptane/ionic-liquid/water system was performed to study the effect of hydrophobic and hydrophilic ionic liquids (ILs) on the interfacial structure of heptane/water as a model for oil/water systems. The results are compared with the simulated water/sodium-dodecyl-sulfate (SDS)/heptane interface. Also, the self-assembly and orientation of ILs and SDS molecules at heptane/vapor interface are studied. We observed that the behavior of these surfactants at heptane/water and heptane/vapor interfaces is very different. The computed density profiles provide a detailed view of the interfacial structure and a route to discuss quantitatively how the oil and water phases organize the surfactant molecules. The effect of ILs [C_<i>n</i>mim]­Cl and [C_<i>n</i>mim]­PF₆ (with <i>n</i> = 4, 8, and 12) and SDS on the interfacial tension of heptane/water was simulated and compared at <i>T</i> = 343.15 K. The results indicate that ILs with long alkyl chain could behave similar to a conventional surfactant

Molecular Dynamics Simulation and Experimental Approach to the Temperature Dependent Surface and Bulk Properties of Hexanoic Acid

For the first time, bulk and surface properties of hexanoic acid was simulated by classical molecular dynamics and compared with corresponding values we measured in the range of <i>T</i> = 298.15–373.15 K at ambient pressure. AMBER and optimized potential for liquid substance all atom (OPLS-AA) force fields plus our calculations for atoms charges enable simulating density, surface tension, and viscosity, as well as the bulk structural and orientational profile of molecules at the hexanoic acid/vapor interface. The simulated densities are in good agreement within 2.9%, and the simulated surface tension within 2% over the whole range of experimental measurement. On the basis of structural studies, the carboxylic headgroups form tight hydrogen bonding, whereas the alkyl chains loosely interact indication of a high electrostatic to van der Waals interaction ratio prevailing the liquid system. The simulated viscosities agree well at high temperatures with experiment, though the agreement is reduced at low temperatures. This can be attributed to describing hexanoic acid system with strong Coulombic interaction, H-bonding, and weak van der Waals interaction all by the same force field. Quite interestingly, the simulated density profile shows an enhancement at the interface characteristic of liquids of high anisotropic molecules and the ionic liquids