Estimation of the Surface Tension of Polar FluidsLong-Range Contributions

Abstract

The theoretical prediction of the surface tension of polar fluids is considered with the focus on the long-range contributions arising due to orientational correlations among the dipoles. A set of three different methods are applied to a simple model of a polar fluid: (i) A very simple analysis is presented based on an effective dipole−dipole potential and the use of the generalized van der Waals (GvdW) density functional theory which has proven to be quite accurate for Lennard-Jones fluids. The effective dipole−dipole potential retains, in a low-order approximation, the Lennard-Jones form of the full potential but adds temperature dependence to the potential parameters. (ii) Molecular dynamics (MD) simulations provide a far more accurate account of the short-range interaction in the polar fluid but suffer from numerical difficulties associated with the need for a cutoff on the range of the interaction to which the surface tension is particularly sensitive. (iii) For this reason we introduce a hybrid MD/GvdW theory wherein the long-range contribution to the surface tension is estimated by the corresponding term in the GvdW result. Applications to the single-component fluids composed of HCl or HBr are presented. The interaction potential is taken to be of either Stockmayer form or a closely related form where the dipole moment is created by two point charges. The results show that the GvdW estimate agrees reasonably with experiment, and MD simulation and MD/GvdW calculation improves the convergence of the MD estimate by inclusion of both direct long-range interaction and indirect effects due to changes in the bulk phases.

Description of Ionic Surfactant/Water System by Adjusting Mesoscopic Parameters

“…However, until now, there has been no theory to quantitatively correlate these interactions with conservative interaction parameters. Surface tension is an overall description of the interactions between molecules in two phases. − Consequently, we adjusted conservative interaction parameters directly and chose surface tension to qualitatively correlate microinteractions of small molecule surfactants in aqueous solution with mesoscopic conservative interaction parameters in the present research. In addition, the variation of surface tension was used to monitor the effect caused by the adjustment of repulsion interactions among surfactant head and tail, water, and air.…”

Investigation of Micro Solid Immersion Lens Mounting Systems

“…Gubbins and co-workers [25] performed a Molecular Dynamics (MD) simulation of the Stockmayer fluid and indeed found parallel alignment on the liquid side of the interface, in qualitative accord with theory, but simulation data were inconclusive for the vapour side. The same fate befell another MD simulation of the same system, by Nordholm and co-workers [26], as well as simulations of TIPT4 water (as modelled by Sullivan et al [18,19]), by Pohorille and co-workers [27][28][29], and by Matsumoto and Kataoka [30,31]: whereas dipoles in the liquid could be reliably said to prefer parallel orientations, no such certainty was borne out as regards the vapour. Very recently, however, Winkelmann and co-workers [32] carried out very careful MD simulations of a thin layer of: (i) Stockmayer molecules; and (ii) dipolar Lennard-Jones (LJ) dumbbells of small elongation.…”

Development of corresponding states model for estimation of the surface tension of chemical compounds

“…Since that time, lots of efforts have been undertaken for the determination of surface tension of pure compounds. These new works have been mainly based on parachor parameter, modification of the original correlation of Macleod, corresponding state principles, molecular dynamics (MD) simulations, finite‐size scaling approach, transferable potentials for phase equilibria (TraPPE), and optimized potentials for liquid simulations (OPLS) force fields, equations of state, molecular layer structure theory (MLST), correlation between surface tension and liquid compressibility, and statistical‐mechanic accompanied by corresponding state principle . A rigorous review on these methods has been already well‐presented .…”