Bioinspired low wettable surfaces: engineering of hard and soft materials via processing of smart coatings for different industrial applications

M. Raimondo
ISSMC CNR Institute of Science, Technology and Sustainability for the Development of Ceramic Materials, National Research Council,
Italy

Keywords: coatings, superhydrophobicity, antifouling, anti-icing, slippery, surfaces

Summary:

Today, many industries need of innovative and flexible solutions allowing to make of the same bulk material a new multifunctional one, with an improved added value, to be easily integrated in the production lines on a large scale. Wettability against liquids is a fundamental property of a solid surface, whose control plays a key role on industrial ceramic, glass, aeronautic, naval, sectors etc. The assessment of the scientific criteria to reduce wetting – related in a complex way to materials’ chemico/physical features interacting with the surrounding environments and the contact fluids itself – are among the biggest challenges of innovation in materials’ science. In the last ten years, lot of studies have focused on mimicking the outstanding abilities of living organisms to repel water/oily substances and replicate them on synthetic materials; e.g. low wettability of some living organism is related to hierarchically perfectly organized structures. Current knowledge highlights that contact angle CA>150°, CA hysteresis lower than 5° and an extremely reduced surface energy are required to produce i.e. self-cleaning, de-icing, anti-fouling, low friction materials, etc. This work focus on the design of amphiphobic metals, alloys and natural fibres, whose surface behaves simoultaneously as superhydrophobic and oleophobic (repellence against low-surface tension liquids). Nano-oxides suspensions with an average particle size ˂ 30 nm, eventually coupled with perfluorinated, and most lately with fluorine-free lubricants, have been used to modify the material surfaces giving rise to solid-liquid-air and/or solid-liquid-liquid interfaces. Dip and roller coating, and automated spraying were selected as deposition techniques thanks to their feasibility at industrial level. Optically transparent, homogeneous, nanostructured organic/inorganic hybrid coatings, with a thickness in the 200-300 nm range, have been generated by sol-gel or hydrothermal methods, followed by thermal consolidation and introduction of low energy external layers. CA with water as high as 178°±1° were obtained, the same materials presenting excellent de-wetting phenomena, as certified by the CA hysteresis lower than 5°±1°. A full characterization of the coatings chemistry (XPS, FESEM) and structuring (flower-like lamellas, agglomeration of spherical nanoparticles, etc) was undertaken and the relationships with slippery, antifouling, antiacing/deicing etc. behaviour were assessed. The scaling-up of the different solutions, also clamping on their durability under real conditions, are discussed according to different working scenarios. To date, the results of this work let us think that the planning of innovative smart materials, bringing great convenience in strategic industrial processes, it is a feasible task.