Today, many different 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 is a fundamental property of a solid surface, whose control plays a key role in industrial sectors such as the ceramic and glass ones, aerospace, naval or maritime, electronic and mechanical, and so on. The assessment of the scientific criteria to modulate the wetting - which depends in a complex way on surface chemistry and structural features interacting with the surrounding working environments and contact fluids - are among the biggest challenges of innovation in the field of materials' science. In the last ten years, a lot of studies have focused on the possibility of mimicking the outstanding ability of living organisms to repel water and/or oily substances, trying to replicate it on synthetic materials. The basic concepts to design functional materials with a controlled wettability draw inspiration from the perfectly, mostly hierarchically, organized structures allowing the natural organisms to actively interact with the surrounding environment. Current knowledge highlights that high static contact angle (CA>150°), CA hysteresis (difference between the advancing and receding CAs in dynamic sliding/rolling of a fluid drop) lower than 5° and an extremely reduced surface energy are required to produce i.e. self-cleaning materials, de-icing, anti-fouling, low friction components as well, etc. This lecture will focus on experimental activities relating to the design of amphiphobic glasses and ceramics, metals and alloys, whose surface behaves simoultaneously as extremely repellent to water (superhydrophobicity) and low-surface tension liquids (oleophobicity). Nano-oxides suspensions with an average particle size of less than 30 nm, eventually coupled with perfluorinated, lubricant compounds, have been used to modify the material surfaces giving rise to solid-liquid-air working interfaces or, alternatively, to solid-liquid-liquid ones. Dip coating and automated spraying were selected as deposition techniques thanks to their high transfer degree and industrial feasibility. Optically transparent, homogeneous, nanostructured organic/inorganic hybrid coatings, with a thickness commonly in the 200-300 nm range that if any can be implemented up to some microns, have been generated by sol-gel method, followed by thermal processing and introduction of low energy elements. Static contact angles with water as high as 178°±1° were obtained, the same materials presenting excellent de-wetting phenomena, as certified by the contact angle hysteresis lower than 5°±1°. A full characterization of the surface chemistry was undertaken by XPS analyses, highlighting the different coating's components in the hybrid structure, while FESEM observations allowed to estimate the coating's thickness (300-400 nm) and the structural features (flower-like lamellas, agglomeration of spherical nanoparticles, etc) of coatings. The potential applications of amphiphobic materials clamp on durability under different conditions (i.e. chemically aggressive environments, presence of mechanical stresses, friction effects, etc), so that materials' scientists are even more asked to design lasting products able to keep unchanged their performances over the time. Good mechanical resistance and durability to wearing phenomena, anti-frost performances and resistance to chemical attacks of properly designed functional surfaces will be presented, according to different scenarios. The obtained results encourage to think that durable smart materials can be planned, bringing great convenience in many strategic industrial processes.
Industrial materials: the challenges for smart coatings
Raimondo Mariarosa
2017
Abstract
Today, many different 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 is a fundamental property of a solid surface, whose control plays a key role in industrial sectors such as the ceramic and glass ones, aerospace, naval or maritime, electronic and mechanical, and so on. The assessment of the scientific criteria to modulate the wetting - which depends in a complex way on surface chemistry and structural features interacting with the surrounding working environments and contact fluids - are among the biggest challenges of innovation in the field of materials' science. In the last ten years, a lot of studies have focused on the possibility of mimicking the outstanding ability of living organisms to repel water and/or oily substances, trying to replicate it on synthetic materials. The basic concepts to design functional materials with a controlled wettability draw inspiration from the perfectly, mostly hierarchically, organized structures allowing the natural organisms to actively interact with the surrounding environment. Current knowledge highlights that high static contact angle (CA>150°), CA hysteresis (difference between the advancing and receding CAs in dynamic sliding/rolling of a fluid drop) lower than 5° and an extremely reduced surface energy are required to produce i.e. self-cleaning materials, de-icing, anti-fouling, low friction components as well, etc. This lecture will focus on experimental activities relating to the design of amphiphobic glasses and ceramics, metals and alloys, whose surface behaves simoultaneously as extremely repellent to water (superhydrophobicity) and low-surface tension liquids (oleophobicity). Nano-oxides suspensions with an average particle size of less than 30 nm, eventually coupled with perfluorinated, lubricant compounds, have been used to modify the material surfaces giving rise to solid-liquid-air working interfaces or, alternatively, to solid-liquid-liquid ones. Dip coating and automated spraying were selected as deposition techniques thanks to their high transfer degree and industrial feasibility. Optically transparent, homogeneous, nanostructured organic/inorganic hybrid coatings, with a thickness commonly in the 200-300 nm range that if any can be implemented up to some microns, have been generated by sol-gel method, followed by thermal processing and introduction of low energy elements. Static contact angles with water as high as 178°±1° were obtained, the same materials presenting excellent de-wetting phenomena, as certified by the contact angle hysteresis lower than 5°±1°. A full characterization of the surface chemistry was undertaken by XPS analyses, highlighting the different coating's components in the hybrid structure, while FESEM observations allowed to estimate the coating's thickness (300-400 nm) and the structural features (flower-like lamellas, agglomeration of spherical nanoparticles, etc) of coatings. The potential applications of amphiphobic materials clamp on durability under different conditions (i.e. chemically aggressive environments, presence of mechanical stresses, friction effects, etc), so that materials' scientists are even more asked to design lasting products able to keep unchanged their performances over the time. Good mechanical resistance and durability to wearing phenomena, anti-frost performances and resistance to chemical attacks of properly designed functional surfaces will be presented, according to different scenarios. The obtained results encourage to think that durable smart materials can be planned, bringing great convenience in many strategic industrial processes.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
