Background: This study used molecular dynamics simulations to investigate the wetting properties of a droplet on copper surfaces with different nanostructures to determine the influence of the structural parameter and roughness factor on the wetting properties.
Methods: The simulation results show that the structural parameter h/b can determine the wetting transition of droplets on surfaces. In addition, the critical structural parameter values are 1.5, 1.5, 2.08 and 2.24 for the square pillar, cylinder, frustum and cone nanostructures, respectively. Due to the restriction of the wedge surface on water molecules, the effect of the wedge surface is not the same when the theoretical gap and height of the nanostructures are changed on different surfaces.
Results and Discussion: For the square pillar and the cylinder surfaces, when changing the height or the theoretical gap of the nanostructure, the wedge angle is always the same and is 90°, so the effect of the wedge surface is unchanged for water molecules. For the frustum and the cone surfaces, the wedge angle does not change when the theoretical gap of the nanostructure is changed but when the height of the nanostructure is changed, the wedge angle gradually increases but does not exceed 90° resulting in the restriction of the wedge surface on water molecules gradually increasing. Therefore, for the same height and theoretical gap, the contact angle of the frustum and the cone surfaces is larger than that of the square pillar surfaces and cylinder surfaces due to the effect of the wedge surface. It is also observed that the increased roughness factor helps increase the contact angle of the droplet.
Conclusion: We propose that the wetting properties of the nanostructure surface can be controlled by the structural parameter associated with the surface roughness.