Analysis of the Subcritical Carbon Dioxide-Water Interface

作者：Zhang Hui; Singer Sherwin J^*

来源：Journal of Physical Chemistry A, 2011, 115(23): 6285-6296.

DOI：10.1021/jp200190k

We follow the evolution of the H2O/CO2 interface at 300 K from the low pressure limit to near-critical pressures in molecular dynamics simulations using the SPC water and EPM2 carbon dioxide models. The intrinsic structure of the interface is elucidated by accumulating density profiles relative to the fluctuating capillary wave surface. Our main finding is that a carbon dioxide film of increasing density and thickness grows in two stages at the interface while the structure of the water surface barely changes. At low density, the entire film density profile grows linearly with the bulk CO2 density. This regime continues up to a bulk CO2 density of roughly 0.00095 angstrom(-3). At pressures above this point, we observe a distinct second peak in the CO2 density, along with a tail of excess density that decays exponentially with distance from the interface. The decay length of the exponential tail diverges with increasing CO2 pressure according to an inverse power law decay. Over the entire range of pressures, the CO2 film had no detectable effect on the orientational order of the water surface. As expected, when the film of excess CO2 at the interface grows, we find that the surface tension drops with increasing pressure. This is in qualitative accord with existing measurements, although the rate at which the surface tension falls with increasing pressure according to the SPC and EPM2 models is too small, indicating that the surface excess of CO2 is underestimated by these models.

• 出版日期2011-6-16