Water–Carbon Interactions 2: Calibration of Potentials using Contact Angle Data for Different Interaction Models

Abstract

Molecular dynamics simulations of water droplets on graphite are carried out to determine the contact angle for different water–carbon potential functions. Following the procedure of Werder et al. [J. Phys. Chem. B, 107 (2003) 1345], the C–O Lennard–Jones well depth is varied to recover the experimental value for the contact angle {\rm (84 -- 86 ^\circ )} using a 2000-molecule water droplet and compensating for the line tension effect that lowers the contact angle for increasing droplet size. For the discrete graphite surface model studied by Werder et al., the effects of adding C–H Lennard–Jones interactions and changing the long-range cut-off distance are considered. In addition, a continuum graphite surface model is studied for which the water–graphite interaction energy depends only on the normal distance (z) from the water oxygen to the surface. This new model, with z -10 repulsion and z -4 attraction, is formulated in terms of the standard Lennard–Jones parameters, for which the recommended values are sgr CO=3.19 Å and ε CO=0.3651 kJ/mol.