Superhydrophobic nickel coating fabricated by 3D printing-like scanning electrodeposition

Superhydrophobic surfaces have been widely studied for potential applications in numerous areas owing to their excellent properties. Natural phenomena have extensively inspired the fabrication of superhydrophobic surfaces based on constructing the hierarchical micro-nano structures. Recently, numerous methods including laser pulsing and plasma treatment among others have been developed for their fabrication. However, these methods have limited applications due to their high cost, complexity and require special materials.

The development of the electrodeposition preparation method has been of great benefit in the preparation of superhydrophobic surfaces. This technique has been effectively used to prepare nickel and nickel composites coatings with various surface morphologies at relatively low costs. Despite its effectiveness, electrodeposition involves chemical modification. This involves soaking in organic compounds to complete surface post-treatments which leads to additional cost.

To this note, Nanjing University of Aeronautics and Astronautics researchers: Professor Lida Shen, Mingzhi Fan, Associated Professor Mingbo Qiu, Wei Jiang, and Zhanwen Wang assessed the feasibility of fabricating superhydrophobic surfaces via 3D printing-like scanning electrodeposition process without chemical modification. Apart from simplifying the fabrication process, the authors purposed to eliminate the negative environmental impacts brought about by the use of organic compounds during chemical modification as well as enhance the hydrophobic properties of the coatings. The work is currently published in the journal, Applied Surface Science.

For illustration, superhydrophobic nickel coatings were directly fabricated using the proposed method without chemical modification. The microstructure, wettability, and surface chemical composition properties were characterized using various methods such as scanning electron microscopy. Thus, they also investigated the factors affecting the preparation of superhydrophobic surfaces as well as the advantages of scanning electrodeposition over conventional electrodeposition methods.

Regarding the occurrence of deposition with the movement of the anode nozzle, the method exhibited a selective deposition process. Due to its flexibility and portability, it was possible to adjust the shape and outlet dimension of the nozzle. As such, it recorded a relatively higher deposition efficiency as compared to the conventional electrodeposition process. This was attributed to the continuous spraying of the solution on the cathode surface thus reducing the polarization concentration and increasing the applied current density.

The fabricated superhydrophobic nickel coating contained cauliflower-like clusters with hierarchical micro-nano structures induced by the tip effect. Even though the newly prepared coating was not superhydrophobic, it exhibited superhydrophobic properties after being exposed to air for a week. For instance, a contact angle of 6µL water droplet on the surface reached 155.4^° at a sliding angle of 6.5^°. As depicted by the unchanged micro-morphology of the coating during storage, change in the wettability was initiated by the adsorption of organic compounds. This led to the conclusion that low surface energy and hierarchical micro-nano structure are the key factors affecting the fabrication of superhydrophobic surfaces.

In general, the scanning electrodeposition method is a flexible, controllable, simple and fast method for the preparation of coating with excellent superhydrophobic properties. By eliminating the chemical modification process, it further eliminates the possible effects on the environment thus it is an environment friendly fabrication method. With the similar idea of 3D printing, the superhydrophobic coating can be directly, selectively and on-site prepared on the surface of structural parts by using industrial robots or other driving platforms in the future. The study by Professor Lida Shen and colleagues will, therefore, promote the devolvement and use of superhydrophobic surfaces in numerous practical applications.