On the Water-Carbon Interaction for Use in Molecular Dynamics Simulations of Graphite and Carbon Nanotubes

A systematic molecular dynamics study shows that the contact angle of a water droplet on graphite changes significantly as a function of the water-carbon interaction energy. Together with the observation that a linear relationship can be established between the contact angle and the water monomer binding energy on graphite, a new route to calibrate interaction potential parameters is presented. Through a variation of the droplet size in the range from 1000 to 17 500 water molecules, we determine the line tension to be positive and on the order of 2 x 10-10 J/m. To recover a macroscopic contact angle of 86°, a water monomer binding energy of -6.33 kJ mol-1 is required, which is obtained by applying a carbon-oxygen Lennard-Jones potential with the parameters ϵCO = 0.392 kJ mol-1 and δCO = 3.19 Å. For this new water-carbon interaction potential, we present density profiles and hydrogen bond distributions for a water droplet on graphite.