Energy conversion based on superhydrophobic surfaces

Fabrication of Bulk Tungsten Microstructure Arrays for Hydrophobic Metallic Surfaces Using Inductively Coupled Plasma Deep Etching

Hydrophobic surfaces have attracted great attention due to their ability to repel water, and metallic surfaces are particularly significant as they have several benefits, for example they self-clean and do not corrode in marine environments, but also have several applications in the aircraft, building and automobile industries. Tungsten is an ideal material for metallic surfaces due to its remarkable mechanical properties. However, conventional micromachining methods of micro- or nanostructures, including mechanical fabrication and laser and wet etching are incapable of balancing functionality, consistency and cost. Inspired by the etching process of silicon, deep etching of bulk tungsten has been developed to achieve versatile microstructures with the advantages of high efficiency, large scale and low cost. In this article, fabrication methods of tungsten-based hydrophobic surfaces using an ICP deep etching process were proposed. Micro- or hierarchical structure arrays with controllable sidewall profiles were fabricated by optimizing etching parameters, which then exhibited hydrophobicity with contact angles of up to 131.8°.

Wettability Controlled Surface for Energy Conversion

To achieve clean and high-efficiency utilization of renewable energy, functional surfaces with controllable and patternable wettability are becoming a fast-growing research focus. In this work, a laser scribing strategy to fabricate patterned graphene surfaces that are capable of energy conversion in different forms is demonstrated. Using the laser raster-scanning and vector-scanning modes, two distinct surface structures are constructed on polybenzoxazine substrate, yielding a superhydrophilic (LSHL) surface and superhydrophobic (LSHB) surface, respectively. Of particular note is that the unique hierarchical structure of LSHB surface has endowed it with quite a robust superwetting behaviors. Further profiting from the flexibility of the processing method, wettability patterns with spatially resolved LSHL and LSHB regions are designed, achieving the conversion of surface energy to liquid kinetic energy. This also offers a tractable approach to fabricate wettability-engineered devices that enable the directional, pumpless transport of water by capillary pressure gradient and the selective surface cooling via jet impingement. In addition, the LSHB surface demonstrates the high conversion of electric-to-thermal energy (222 °C cm² W^-1 ) and light-to-thermal energy (88%). Overall, the material system and processing method present a promising step forward to developing easy-fabricated graphene surfaces with spatially controlled wettability for efficient energy utilization and conversion.

A Review of Fabrication Methods, Properties and Applications of Superhydrophobic Metals

Hydrophobicity and superhydrophobicity with self-cleaning properties are well-known characteristics of several natural surfaces, such as the leaves of the sacred lotus plant (Nelumbo nucifera). To achieve a superhydrophobic state, micro- and nanometer scale topography should be realized on a low surface energy material, or a low surface energy coating should be deposited on top of the micro-nano topography if the material is inherently hydrophilic. Tailoring the surface chemistry and topography to control the wetting properties between extreme wetting states enables a palette of functionalities, such as self-cleaning, antifogging, anti-biofouling etc. A variety of surface topographies have been realized in polymers, ceramics, and metals. Metallic surfaces are particularly important in several engineering applications (e.g., naval, aircrafts, buildings, automobile) and their transformation to superhydrophobic can provide additional functionalities, such as corrosion protection, drag reduction, and anti-icing properties. This review paper focuses on the recent advances on superhydrophobic metals and alloys which can be applicable in real life applications and aims to provide an overview of the most promising methods to achieve sustainable superhydrophobicity.