Abstract
A modern environmental safety approach requires the implementation of green or sustainable strategies, such as banning or significantly lowering the presence of harmful substances on the market or in the industrial environment. To date, the majority of highly performing solutions are still based on fluorine chemistry, even with a growing effort to lower its impact. Economic costs, but also persistence, long-term degradation, and transformation in the environment can raise issues about medium- and long-term effects on human health and wildlife. Coatings with high water and oil repellence are used worldwide in daily life and in industrial and research fields, such as self-cleansing, anti-icing, and anti-biofouling. The combination of a particular geometry or surface structure and low-energy materials results in unique properties related to a range of materials in natural or synthetic categories aiming to build, when possible, a fluorine-free world. This work revises recent and key literature to propose valid alternatives to fluoro compounds in terms of water and oil repellence, as well as stability and resistance to physico-chemical agents. In this paper, natural compounds like fatty acids and waxes are addressed together with more synthetic systems like silicon-based solutions, and polymeric and inorganic nanostructured coatings. Most of the revised papers deal with topics fulfilling environmental requirements but are mainly restricted to highly repellent water and aqueous systems. Nevertheless, new and sustainable strategies for providing suitable, highly oleophobic surfaces to lower fluorine presence have been reported from a small but growing body of literature.
Highlights
IntroductionA green or sustainable approach to chemistry requires that unsafe products are banned or significantly lowered in their presence during chemical production and processes
A green or sustainable approach to chemistry requires that unsafe products are banned or significantly lowered in their presence during chemical production and processes.Most of the issues are related to economical costs, but are derived in terms of persistence, long-term degradation, and transformation in the environment with mediumto long term-effects on human health and wildlife [1].High water and oil repellence has become a recommended feature in daily life, and industrial and research fields, such as self-cleansing, anti-icing, and anti-biofouling
The work of Heale et al [54] reports that the authors studied the effects of fatty acid alkyl chain length on wettability of coated hydrophobic SiO2. They used octanoic, decanoic, dodecanoic, hexadecenoic, and octadecanoic acids that were separately mixed in ethanol with SiO2 particles (0.5–1.0 mm diameter) and hydrophobic surfaces were obtained for drop cast or spray coating on a glass substrate
Summary
A green or sustainable approach to chemistry requires that unsafe products are banned or significantly lowered in their presence during chemical production and processes. High water and oil repellence has become a recommended feature in daily life, and industrial and research fields, such as self-cleansing, anti-icing, and anti-biofouling Such specific surface properties are related to the presence of a particular geometry or surface structure combined with low-energy materials conferring their unique wettability features. There are many molecules or atoms that have less binding with the nearby molecules or atoms than the atoms or molecules in the bulk, and the molecules at the interface have the potential and the necessity to make new bonds Depending on their material composition, the interfaces exhibit different behaviours; high energy of an interface causes wetting of the solid surface and spreads the liquid on it while low energy produces non-wetting interfaces. If it is possible to assume that the temperature and the pressure is constant, and that there is no adsorption at the interfaces, the two concepts are numerically equivalent to each other
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