Interfacial Behavior of Methane in Methane/ p ‐Xylene/Water Systems: First Principles Inspected Using Neutron Imaging and Molecular Dynamics Simulations

ABSTRACT Pressurized gases adsorb on the gas‐liquid ( g ‐ l ) interfaces, thus reducing the interfacial tension (IFT). Gas‐saturated liquid–liquid ( l ‐ l ) emulsions occur in oil and gas wells, possible IFT changes due to saturation remain unclear. We study if the IFT reduction occurs for the model system of methane, p‐ xylene, and water. The neutron imaging (NI) observations of bulk ( g ‐ l ‐ l ) systems at 100 bar provide several quantities simultaneously from each experimental run, e.g., IFT for g ‐ l and methane diffusivity for the p‐ xylene rich phase, but does not sensitively provide IFT for the l ‐ l interface. The quantities derived for the p‐ xylene‐rich phase using NI allows us to calibrate molecular dynamics (MD) simulation, which is used for the predictions of IFT for l ‐ l , literature data for binary benzene/water ( l ‐ l ) system are used as the reference. Overall, no, or very minor effect (±1 mN m ^{− 1} ) on IFT is robustly found up to methane saturation at 100 bar. Variation of partial charges on the p ‐xylene model from zero to quantum calculation‐based modulate the fine structure of p ‐xylene/water interface and has small, yet qualitative effect on IFT, resulting in a weak adsorption (−1 mN m ⁻¹ ), or weak depletion (+1 mN m ⁻¹ ) of methane from l‐l .