How do ions contribute to brine-hydrophobic hydrocarbon Interfaces? An in silico study.

The saltwater-oil interface is of broad implication in geochemistry and petroleum disciplines. To date, the main focus has been on the surface contribution of polar, heavy compounds of crude oil, widely neglecting the role of non-polar hydrocarbons. However, non-polar compounds are expected to contribute to characteristics of oil-brine interfaces. Utilizing molecular dynamics simulation, we aim to characterize ion behavior adjacent to hydrophobic organic phases. Concerning natural environments, NaCl, CaCl Ions accumulate nearby the intrinsically charge-neutral oil surfaces. A disparate surface-favoring propensity of ions causes the interfacial region to resemble an electrical layer and impose an effective surface charge onto the oil surface. Despite absence of any polar site, the effective surface charge density is hydrocarbon-dependent, with the highest and lowest values observed for toluene and heptane interfaces, respectively. Due to accumulation of toluene molecules nearby the brines, the interfacial characteristics of heptol (toluene-heptane mixture) is comparable to that of the toluene phase.

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Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.