Cassie-State Stability of Metallic Superhydrophobic Surfaces with Various Micro/Nanostructures Produced by a Femtosecond Laser

Abstract

The Cassie-state stability plays a vital role in the applications of metallic superhydrophobic surfaces. Although a large number of papers have reported the superhydrophobic performance of various surface micro/nanostructures, the knowledge of which kind of micro/nanostructure contributes significantly to the Cassie-state stability especially under low temperature and pressure is still very limited. In this article, we fabricated six kinds of typical micro/nanostructures with different topography features on metal surfaces by a femtosecond laser, and these surfaces were modified by fluoroalkylsilane to generate superhydrophobicity. We then systematically studied the Cassie-state stability of these surfaces by means of condensation and evaporation experiments. The results show that some superhydrophobic surfaces, even with high contact angles and low sliding angles under normal conditions, are unstable under low temperature or external pressure. The Cassie state readily transits to a metastable state or even a Wenzel state under these conditions, which deteriorates their superhydrophobicity. Among the six micro/nanostructures, the densely distributed nanoscale structure is important for a stable Cassie state, and the closely packed micrometer-scale structure can further improve the stability. The dependence of the Cassie-state stability on the fabricated micro/nanostructures and the laser-processing parameters is also discussed. This article clarifies optimized micro/nanostructures for stable and thus more practical metallic superhydrophobic surfaces.

Anisotropic Sliding of Water Droplets on the Superhydrophobic Surfaces with Anisotropic Groove‐Like Micro/Nano Structures

“…The laser processing experiments were performed in atmospheric environment under normal incidence of the laser beam. More detailed information about the laser irradiation setup can be found in our previous papers …”

Facile Synthesis and Self‐Cleaning Application of Bimetallic (CuSn, CuNi) Dendrites

“…However, due to the UV sensitivity and scalability issues of these materials, research effort is being focused for metallic nanostructures that can be fabricated in a scalable fashion with no UV susceptibility. Noteworthy here, reports on gaining comprehensive insight to the physics of the wetting properties of these metallic dendritic materials is very limited . As demonstrated here, the fabricated CuSn and CuNi bimetallic dendrites naturally have high degree of micro‐nano structured roughness, and hence increased number of interfaces, that can be exploited for their applications in SHS.…”

“…This is in stark contrast to the morphology of the CuSn dendrites where the structures are less dense and slightly random with non‐periodic growth, albeit with dual degree of roughness. It is important to note that the differences in the morphologies and the various degrees of roughness present within these dendrites are known, to have a dramatic impact in conferring different degree of wetting properties to these surfaces. We exploit this different degree of micro/nano structuring in these dendrites for preparing superhydrophobic surfaces with excellent self‐cleaning properties as discussed later in this report.…”

Long term superhydrophobic and hybrid superhydrophobic/superhydrophilic surfaces produced by laser surface micro/nano surface structuring

“…A range of structures with different wettability characteristics were produced using fs, ps and ns lasers. For example, fs laser was used to produce structures of different wettability characteristics on silicon [13][14][15][16][17], PDMS silicone elastomer polymer [18][19][20], glass silica [21], titanium [22], stainless steel [23][24][25], Polypropylene polymer [26] and cupper [27,28].…”