Is Water at the Graphite Interface Vapor-like or Ice-like?

Area of Science:

• Atmospheric Chemistry
• Materials Science
• Physical Chemistry

Background:

• Graphitic surfaces, key components of atmospheric aerosols like soot, exhibit varied ice nucleation efficiencies.
• Experimental data suggests pure graphite has negligible ice nucleation ability, contrasting with molecular simulation predictions.

Purpose of the Study:

• Investigate the discrepancy between experimental and simulated ice nucleation efficiencies of graphite.
• Elucidate interfacial thermodynamic contributions (free energy, enthalpy, entropy) to water-graphite and water-ice binding.
• Determine if the monatomic water model (mW) accurately captures these interfacial properties.

Main Methods:

• Employed thermodynamic analysis and free energy calculations.
• Utilized the monatomic water model (mW) with parameterized water-carbon interactions.
• Analyzed water-graphite, water-ice, and ice-water interfacial properties.

Main Results:

• Liquid water at the graphite interface exhibits bulk-like thermodynamic properties (free energy, entropy, enthalpy).
• The mW model accurately reproduces the thermodynamics of the water-graphite interface.
• Positive binding entropy between graphite and ice is dominated by reduced ice-water interface, consistent across experiments and simulations.

Conclusions:

• The discrepancy in ice nucleation efficiency arises from the mW model's inability to simultaneously reproduce experimental contact angles and ice-graphite interface free energy.
• This limitation is attributed to the model's coarse resolution and lack of rotational degrees of freedom.
• Further model development is needed for accurate prediction of heterogeneous ice nucleation on graphitic surfaces.