Coupling Diffusion Welding Technique and Mesh Screen Creates Heterogeneous Metal Surface for Droplets Array

Nonsilicon micromachining is a challenge, especially for large scale heterogeneous (hydrophilic/hydrophobic) surface fabrication. Here, mesh screen and diffusion welding technique are coupled to form a novel fabrication method. Mesh screen is used as mask. The diffusion welding technique sinters mesh screen on copper surface to form welding junction array. Chemical treatment of sintered package forms superhydrophobic nanostructures on surfaces except welding junction array. Separating mesh screen from copper substrate exposes hydrophilic dots array, corresponding to welding junction array. Thus, heterogeneous surface is created. By condensing wet air, main droplet and neighboring droplet occur on hydrophilic dot and superhydrophobic part, respectively. For horizontal surface, neighboring droplets initially generated on nanograsses behave consecutive events of coalescence, jump, and return, triggering contact/noncontact effect induced jumping. Thus, defect droplet area is formed and droplet size uniformity is broken. A nondimensional equation is proposed for the contact effect induced jumping analysis. Noncontact effect induced jumping is found for the first time. For vertical surface, droplet array behaves monodisperse size due to departure of merged neighboring droplets without returning, and equal opportunities of neighboring droplets captured by main droplets. The work opens a new way for large scale droplet array generation by controllable condensation.