Three-Dimensional Density Functional Theory Study Of Heterogeneous Nucleation Of Droplets On Rough Solid Surfaces

Understanding of the structure and properties of fluid on rough surfaces is important to many of Chemical production applications. When fluid contacts with microscale rough surfaces, geometry and chemical composition of the surface not only determine the density distribution of fluid and interfacial tension, but also determine the corresponding free energy barriers and the critical radii.A new grand canonical method combined with DFT was applied to calculate the first-order phase transition. This method can calculate not only the first-order gas-liquid phase transition, but also the first-order solid-liquid, gas-liquid-solid and liquid-liquid-solid phase transitions. The results of this method are consistent with the classic equal area method but have a greatly simplified calculation process.The density distributions and droplet nucleation behaviors of Lennard-Jones fluid on plate and three kinds of rough walls were investigated using3D-DFT on the base of first-order transition. comparing the nucleation of droplets at plate and rough walls, we finds that:(1) If the contact angle is larger than90°, plate is more easy to nucleate than rough walls. As the roughness of surface increases, the difficulty of nucleation increases. Once the contact angle is less than90°, the rough plate is more easy to nucleate. The difficult of nucleation decreases with the increasing roughness.(2) The attractive strength of the surface has an obvious effect on the density distribution and droplet nucleation of Lennard-Jones fluid on rough surface. As the strength decreases, the hydrophobicity of the surface increases, the nucleation free energy barrier and nucleation radius also increase.The droplet nucleation on the amorphous polyethylene, amorphous polypropylene, amorphous polystyrene were further investigated. It was shown that that:(1) these polymer surfaces are hydrophobic;(2) the groups on polymer surface have large effects on droplet nucleation. Under the same conditions, the contact angle is amorphous polystyrene> amorphous polypropylene> amorphous polyethylene.