Nanoscale Surface\nTension, Adsorption Isotherms and\nSeparation of Water–Ethanol Mixtures Confined between Graphene-Based\nSlit Pores

Confined water–ethanol mixtures between graphene-based\nslit\npores are studied using grand-canonical Monte Carlo and molecular\ndynamics simulations to connect the adsorption isotherm with nanoscale\nsurface tension. We highlighted preferential interactions between\nethanol and graphene, indicating high selectivity and suggesting that\nthe graphene pore is effective for separating water from ethanol.\nEthanol molecules act as precursors to trigger water adsorption due\nto favorable hydrogen bond interactions. We shed light on a nonmonotonic\nbehavior of surface tension that closely follows the adsorption isotherm.\nWe demonstrate that the decrease in surface tension is a consequence\nof the negative ethanol–ethanol surface tension contribution,\nin line with a specific interfacial organization leading to an “intramolecular”\nphase separation. Additionally, we show the existence of local phase\nseparation between water and ethanol close to the solid surface, where\nethanol molecules are preferentially adsorbed, forming a first interfacial\nlayer with less water and a second layer rich in water. This generates\na multilayer organization and an interfacial microphase separation.\nBy using a gravitational field mimicking the confinement effect, we\nnumerically and experimentally highlight that the water–ethanol\ninterface between two bulk phases is gravitationally stabilized.