Molecular dynamics investigation on the vapor–liquid interface behavior of long-chain alkanes, alcohols, and their mixtures

Abstract

The accurate description of the liquid–vapor interface behavior of higher alkanes and alcohols is an important topic in many petroleum and chemical industries. This research provides molecular-level information on the vapor–liquid interfaces (phase behavior, surface tension, self-diffusion, and solvation structure). Through the use of molecular dynamics simulation, five selected long-chain alkanes (n-dodecane, 5-methyl-undecane), alcohols (1-dodecanol, 1,12-dodecanediol, and 2-butyl-1-octanol), and their mixtures (n-dodecane + 1-dodecanol or 1,12-dodecanediol) have been modeled over a broad temperature range from 323.15 to 573.15 K. The aforementioned properties are qualitatively reproduced using the Optimized Potential for Liquid Simulations–All Atom (OPLS and L–OPLS) and the Transferable Potential for Phase Equilibria–United Atom (TraPPE–UA) force fields, respectively. The current findings are in good agreement with earlier experimental measurements as well as other simulated results. Moreover, the molecule orientations and chain conformation in the bulk liquid area are fully investigated by monitoring the center-of-mass radial distribution function and the probability distributions of end-to-end lengths for certain components. All five hydrocarbons exhibit equivalent propensities for ordering and chain conformation at the interface when subjected to the same isotherm. In addition, we compare the physical and structural characteristic of the unary and binary systems at the same temperature to further investigate the process by which molecular arrangement affects macroscopic thermophysical features. These simulations will provide specific guidance for choosing these widely used force fields to study petrochemical technologies.