Plasma nano-patterning for altering hydrophobicity of copper substrate for moist air condensation

Abstract

Fabrication of durable hydrophobic metallic substrate is an emerging area of research for the condensation process in many industrial devices because its implementation enhances the efficacy of the devices. In this work, effective and durable hydrophobic copper (Cu) substrates were fabricated by plasma nano-pattering. Various discharge voltages were used to create various types of nano-patterns textured on copper substrates. For 30 min of irradiation of Argon gas plasma at various discharge voltages of 500, 650 and 750 V, morphologies of substrates were altered such that micro-litre water droplet has contact angle of 105 ± 3o, 97 ± 5o, and 95 ± 5o, respectively. However, pristine polished Cu substrate has water droplet contact angle of 56±5o. The micro-graph of scanning electron microscope (SEM) showed micro-order to nano-order roughness on etched substrates and the structure of nano-patterns was different for different discharge voltages for given period of argon ions irradiation. The etched copper substrate at 500 V was deployed as a condensing surface for moist air condensation of temperature 28 °C, relative humidity 70% and degree of sub-cooling 10°C. These results showed that the water condensation rate of plasma etching hydrophobic Cu substrate was 438 ml/m2-h, compared to 188 ml/m2-h for pristine Cu substrate.