Analysis of Wettability and Contact Angle Hysteresis on a Thermally Treated Low Free Energy Surface

Abstract

The biomimetic replication of the lotus leaf to create hierarchical surface morphology has attracted significant research interest due to its potential applications in self-cleaning, anti-corrosion, anti-fouling, and anti-icing surfaces. Several attempts have been made to create such structure using metal-fatty acid combination. However, zinc myristate (ZnMTA) surfaces have not been fully explored, despite their relevance and promise in surface engineering. In this study, a superhydrophobic coating was fabricated on a copper substrate through the electrochemical deposition of zinc, followed by thermal annealing and surface modification using myristic acid (MTA). The electrodeposition and annealing processes generated a hierarchical micro–nano surface morphology, whereas surface modification led to the formation of a low-surface-energy ZnMTA layer. Scanning electron microscopy revealed micro-scale clusters decorated with nano-petal structures, producing void spaces capable of trapping air. Quantitative image analysis indicated a void fraction of 86.7 ± 5.4%, which is conducive to the formation of a Cassie–Baxter-type wetting regime. As a result, the coating exhibited excellent water repellency, with a water contact angle of 156° ± 0.8°, contact angle hysteresis of 5°, and roll-off angle or sliding angle of 4°. High-speed imaging of droplet impact further demonstrated droplet rebound with a contact time of 28 ms and a spreading factor of β = 2.33, indicating weak liquid–solid adhesion forces. The combination of hierarchical roughness and low surface energy renders the developed coating promising for applications requiring durable water-repellent surfaces.