A molecular dynamics simulation of a water droplet in contact with a platinum surface

A water droplet in contact with a platinum surface was simulated by the molecular dynamics method. Water molecules were modeled with the well-known SPC/E model and the platinum surface was represented by three layers of harmonic molecules with the constant temperature heat bath model using the phantom molecules. Two types of water-platinum pair potential functions based on extended Hückel calculations were employed, one was developed by Spohr and Heinzinger in 1988 and the other was proposed by Zhu and Philpott in 1994. In the spreading process of a liquid droplet on a platinum surface, the area of contact region between water and platinum expanded just in proportional to the one-third power of time. This spreading rate was clearly in contrast to the case of Lennard-Jones droplet. Even though the water droplet finally spread to a monolayer film on fcc (111) surface with S-H potential, a stable droplet structure on a monolayer film was realized with Z-P potential. The mechanism of the ‘drop on film’ structure was explained by the very concentrated monolayer film of water. Comparing three different platinum surface structures, (111), (100) and (110), contact angle varied drastic and it was largest on fcc (100) surface.