Methane hydration is accompanied by a decrease in entropy and enthalpy, with an overall increase in free energy. In this presentation we address how do these thermodynamic quantities evolve as methane crosses the water-vapor interface. The computational costs associated with atomistic simulations led to much effort directed toward developing coarse-grained models. Here we use the monatomic water model mW, which reproduces many physical characteristics of water without hydrogen atoms or electrostatic, to investigate how accurately mW reproduces the thermodynamic signatures of methane hydration. Our results show a non-monotonous change of the free energy as methane crosses the liquid-vapor interface. A free energy minimum is observed in the vacuum side of the interface. As in the experiment, methane hydration is enthalpically favored and entropically disfavored, with overall positive hydration free energy. We further decompose enthalpy and entropy into contributions of water and methane interactions and interpret the non-monotonous thermodynamic signatures.

Crossing the line: Thermodynamic and structural signatures of methane hydration across the water-vapor interface

245th National Meeting (2013)

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