Preparation of Wettability Gradient Surfaces on a Copper Slide via Solid Liquid Interface Oxidation and COMSOL-Based Simulation for Directional Droplet Movement

A simple approach for preparing wettability gradient surfaces on copper substrates is presented via alkali assistant surface oxidation by using gradual immersion in an NaOH/(NH 4 )S 2 O 8 solution. Additionally, a 2D model was built applying a finite element analysis software (COMSOL) to explain the moving velocity of a droplet and the force applied when moving on the gradient surface. The developed approach is simple, effective, and environmentally friendly. Thus, it could potentially be used in applications requiring heat transfer for the enhancement of the thermal performance of grooved heat pipes.