Abstract

Molecular dynamics simulations are used to explore explosive boiling of thin water films on a gold substrate. In particular, water films of 2.5, 1.6 and 0.7 nanometer thickness were examined. Three different surface wettabilities with contact angles of (in order of increasing hydrophobicity) 11, 47 and 110 degrees were simulated along with substrate temperatures of 400K, 600K, 800K and 1000K. The first wettability was obtained using a Morse interaction potential between the water film and the gold substrate while the other two wettabilities were obtained via a Lennard-Jones potential, adjusting the interaction parameters. Evaporation was the first mode of phase change observed in all cases and explosive boiling did not occur until the substrate reached a temperature of 800K. When explosive boiling was present for all three contact angles, it was consistently shown to occur first for the surface with a 47 degree contact angle. These results suggest that explosive boiling onset is strongly dependent on the particularities of the interaction potential. For instance, the Morse potential used to model the surface described by an 11 degree contact angle, is a smoother potential as compared with Lennard-Jones, but has more interaction sites per molecule - two hydrogen atoms and one oxygen atom vs one oxygen atom. Thus, although the water film reaches a higher temperature with the Morse potential (more so to do with overall interaction strength), the explosive boiling onset is delayed as more interaction sites have to be disrupted.

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