Natural and biomimetic artificial surfaces for superhydrophobicity, self-cleaning, low adhesion, and drag reduction

Selective laser melting of iron-based powder

The purpose of this study was to investigate the influence of Cu-coating on the spreading kinetics and equilibrium contact angles of aluminum on ceramics using a sessile drop technique. Al2O3 and SiC plates were coated by electroless plating. The copper film overcomes the low wetting of the uncoated samples by dissolution in the drop at 800 °C in argon, showing an intrinsically favorable effect on the adhesion energy. Just after 2 min, the contact angle decreased to 12.6° and 26°for Al/Cu–Al2O3 and Al/Cu–SiC, respectively. However, a de-wetting behavior was observed, reaching equilibrium contact angles of 58.3° and 45.5° for the couples. The dissolution reaction rate at the triple junction was so high that the spreading process was controlled by local diffusion rather than chemical reaction kinetics.

Wettability and spreading kinetics of molten aluminum on copper-coated ceramics

The term superhydrophilicity is only 11–12 years old and was introduced just after the explosion of research on superhydrophobic surfaces, in response to the demand for surfaces and coatings with exceptionally strong affinity to water. The definition of superhydrophilic substrates has not been clarified yet, and unrestricted use of this term to hydrophilic surfaces has stirred controversy in the last few years in the surface chemistry community. In this review, we take a close look into major definitions of hydrophilic surfaces used in the past, before we review the physics behind the superhydrophilic phenomenon and make recommendation on defining superhydrophilic surfaces and coatings. We also review chemical and physical methods used in the fabrication of substrates on surfaces of which water spreads completely. Several applications of superhydrophilic surfaces, including examples from the authors' own research, conclude this review.

Hydrophilic and superhydrophilic surfaces and materials

Magnesium is a light metal, with a density two-thirds that of aluminium, is abundant on Earth and is biocompatible; it thus has the potential to improve energy efficiency and system performance in aerospace, automobile, defence, mobile electronics and biomedical applications. However, conventional synthesis and processing methods (alloying and thermomechanical processing) have reached certain limits in further improving the properties of magnesium and other metals. Ceramic particles have been introduced into metal matrices to improve the strength of the metals, but unfortunately, ceramic microparticles severely degrade the plasticity and machinability of metals, and nanoparticles, although they have the potential to improve strength while maintaining or even improving the plasticity of metals, are difficult to disperse uniformly in metal matrices. Here we show that a dense uniform dispersion of silicon carbide nanoparticles (14 per cent by volume) in magnesium can be achieved through a nanoparticle self-stabilization mechanism in molten metal. An enhancement of strength, stiffness, plasticity and high-temperature stability is simultaneously achieved, delivering a higher specific yield strength and higher specific modulus than almost all structural metals.

Processing and properties of magnesium containing a dense uniform dispersion of nanoparticles

Chapter headings and selected sub-headings: Series Preface. Preface. Fundamental Equations of Wetting. Surface and interfacial energies in solid / liquid / vapour systems. Dynamics of Wetting by Metals and Glasses. Non-reactive wetting. Reactive wetting. Methods of Measuring Wettability Parameters. Sessile drop experiments. Surface Energies. Data for metals and alloys. Data for non-metallic compounds. Wetting Properties of Metal / Metal Systems. Effects of alloying elements. Systems that form intermetallic compounds. Wetting Properties of Metal / Oxide Systems. Non-reactive pure metal / ionocovalent oxide systems. Effect of electronic structure of the oxide. Wetting of fluorides. Wetting Properties of Metal / Non-Oxide Ceramic Systems. Metals on predominantly covalent ceramics. Wetting Properties of Metal / Carbon Systems. Non-reactive systems. Reactive systems. Wetting by Glasses and Salts. The glassy state. Wetting behaviour. Wetting When Joining. Flow into capillary gaps. Effects on mechanical properties. Appendices. List of symbols. Index

Michael G. Nicholas

Papers

Wettability at high temperatures