title: 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.
authors.affiliation: Laser Materials Processing Research Centre, School of Materials Science and Engineering, Tsinghua University , Beijing 100084, PR China.
authors.forename: Jiangyou
authors.initials: J
authors.lastname: Long
authors.affiliation: Laser Materials Processing Research Centre, School of Materials Science and Engineering, Tsinghua University , Beijing 100084, PR China.
authors.forename: Lin
authors.initials: L
authors.lastname: Pan
authors.affiliation: Laser Materials Processing Research Centre, School of Materials Science and Engineering, Tsinghua University , Beijing 100084, PR China.
authors.forename: Peixun
authors.initials: P
authors.lastname: Fan
authors.affiliation: Laser Materials Processing Research Centre, School of Materials Science and Engineering, Tsinghua University , Beijing 100084, PR China.
authors.forename: Dingwei
authors.initials: D
authors.lastname: Gong
authors.affiliation: Laser Materials Processing Research Centre, School of Materials Science and Engineering, Tsinghua University , Beijing 100084, PR China.
authors.forename: Dafa
authors.initials: D
authors.lastname: Jiang
authors.affiliation: Laser Materials Processing Research Centre, School of Materials Science and Engineering, Tsinghua University , Beijing 100084, PR China.
authors.forename: Hongjun
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Laser Processing Research Centre, School of Mechanical, Aerospace and Civil Engineering, The University of Manchester , Manchester M13 9PL, England.
authors.forename: Lin
authors.initials: L
authors.lastname: Li
authors.affiliation: Laser Materials Processing Research Centre, School of Materials Science and Engineering, Tsinghua University , Beijing 100084, PR China.
authors.forename: Minlin
authors.initials: M
authors.lastname: Zhong