Effect of nanostructures and wettability on the instability of thin water films on a solid surface: A molecular dynamics study

Molecular dynamics simulations are performed to investigate the stability of thin water films on square gold nanostructures of varying depth and wavelength. The critical film thickness of breakup is shown to increase linearly with nanostructure depth, and is not affected by nanostructure wavelength. In addition, the wettability of the gold surface is controlled from superhydrophilic to hydrophobic by altering the energy parameter of the solid-liquid potential, and the equilibrium contact angle for each energy parameter is calculated using a droplet spreading simulation. Four different energy parameters of the solid-liquid potential are investigated. The ratio of the energy parameter to the energy parameter of water and gold is 1, 0.5, 0.25 and 0.1. The case for ratio of 1 represents water on superhydrophilic gold surfaces. The relationship between the critical film thickness of breakup and the equilibrium contact angle is demonstrated. The results of the present work will provide guidelines for nanostructure design for controlling thin film stability.