Molecular Dynamics Characterization of Temperature and Pressure Effects on the Water-Methane Interface

The water-methane interface plays an important role in mass transfer between the phases. In this work, we employ molecular dynamics to investigate and characterize the mechanics, thermodynamics, and composition of water-methane interfaces applying a unique methodology known as the NP(N)AT ensemble. We systematically increase the pressure (1-50 MPa) and temperature (25-105 degrees C) to calculate the interfacial tension from its mechanical definition. We predict the surface tension via pressure and temperature relations in agreement with the classical scaling laws such as the Eotvos rule. It is found that the surface adsorbs methane molecules as per high interfacial excess and local density of methane. The methane practically remains insoluble in water due to favorable interactions with a dense hydrogen bonded region near the surface. The obtained macroscopic interfacial tension properties and sensitivity to pressure and temperature and the corresponding molecular mechanisms contribute to the evolving understanding and practical applications of this important interface.