Durable Surfaces of Both Wettability Extremes with Stable Dew Harvesting Performance During Liquid–Vapor-Phase Transitions

Abstract

Leveraging micro- and nanoengineering, functional surfaces revolutionize interactions between materials and their environment, leading to a new era of advanced materials. Functional surfaces are capable of providing a wide range of applications, i.e., antifogging, anti-icing, and antiwetting. These surfaces exhibit remarkable adaptability, improving the performance of microfluidic devices, sensors, and MEMS. Superhydrophobic and superhydrophilic surfaces represent the pinnacle of water repellence and attraction, crucial for enhancing applications like dew water harvesting and condensation-related applications, i.e., heat exchangers. To achieve surfaces with such remarkable properties, several delicate processes have been developed, and today’s request is to improve their durability, repeatability, and reusability. In this work, we present a fabrication process for superhydrophilic and superhydrophobic surfaces based on oxygen plasma micro- and nanotexturing, followed by a thin coating deposition of poly(ethylene glycol) (PEG) for superhydrophilicity and plasma deposition of C₄F₈ for superhydrophobicity. It is demonstrated that the surfaces of both wetting extremes exhibit remarkable stability in their wetting properties, maintaining stable water static contact angles (WSCAs) of 161° (for the 9 min plasma micronanotextured superhydrophobic surface) or 0° (for the 9 min plasma micronanotextured and PEG-coated superhydrophilic surface) for more than 4 months of storage in ambient conditions. Superhydrophilic surfaces, which are more prone to wetting property deterioration, are additionally tested using water immersion tests for 14 days, and it is shown that the use of the PEG coating on plasma micronanotextured surfaces enhances the superhydrophilic property stability (WSCA: 25° compared to 63° for the uncoated plasma-textured surface). Finally, the surfaces are probed by dew water harvesting experiments in which no significant performance deterioration is observed and water collection rate (WCR) reduction during aging (after storage) is 20% in the case of the superhydrophobic and less than 5% for the superhydrophilic PEG-coated surface. More vulnerable to wetting, superhydrophilic surfaces are also tested in terms of reusability (i.e., after multiple uses of the same surfaces), and it is found that the WCR decrease is less than 17% (for the 6 min plasma micronanotextured and PEG-coated surfaces).