Nanoscale Hydrophilicity on Metal Surfaces at Room Temperature: Coupling Lattice Constants and Crystal Faces

It is generally accepted that the metal water interface tensions are quite high; thus, the metal surfaces are usually regarded as hydrophilic. Using the molecular dynamics simulations, we have investigated the microscopic wetting behaviors of a series of metal surfaces at room temperature, including Ni, Cu, Pd, Pt, Al, Au, Ag, and Pb with three crystal faces of (100), (110), and (111). We have found that the wetting of the metals is greatly dependent on both the lattice constants and crystal surfaces. Particularly, stable water droplets are found forming on the first ordered water layer, serving as an evidence of room temperature ordered water monolayer that does not completely wet water on Pd(100), Pt(100), and Al(100) surfaces, while water films without ordered water monolayer are found on (110) and (111) faces of all metal surfaces and even (100) face of other metal surfaces (Ni, Cu, Au, Ag, and Pb). The formation of water droplets is attributed to the rhombic ordered water layers on the surfaces, reducing the number of hydrogen bond formation between the monolayers and other water molecules atop the water monolayer. These results demonstrate a tight correlation among the lattice constant, the crystal faces, and the surface wetting behaviors. Our findings of the novel wetting behavior may have potential applications in the surface friction reduction at the metal surfaces, design of the anti-ice materials, and the nonfouling materials.