Molecular dynamics simulation and measurement of contact angle of water droplet on a platinum surface

Abstract

A water liquid droplet in contact with a platinum surface was simulated by the molecular dynamics method. Water molecules were modeled by SPC/E and one layer of harmonic molecules represented the platinum surface with the constant temperature heat bath model using the phantom molecules. Here, the water-platinum pair potential developed by Spohr (1989) based on extended Hückel calculations was employed. In the spreading process of the liquid droplet on the 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. The contact angles of water on a platinum surface under saturated conditions are measured. The measurements are made in a vacuum container using de-ionized and degassed water on a clean platinum surface. The equilibrium static, advancing and receding contact angles are measured by changing the orientation of the platinum surface. The droplets of different masses are placed on the horizontal platinum surface. The surface is the inclined to 20, 30 and 40 degrees. The advancing and receding contact angles under these conditions are measured.