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Superhydrophobic coating technology is regarded as an attractive possibility for the protection of materials in a sea environment. DC techniques are a useful tool to characterize metals' behavior in seawater in the presence/absence of coatings and/or corrosion inhibitors. In this work, investigations concerning Al-5%Mg alloy with and without a sprayed superhydrophobic coating were carried out with potentiodynamic scans in photobiologically active and not active seawater (3 weeks of immersion). In not photobiologically active seawater, the presence of the superhydrophobic coating did not prevent pitting corrosion. With time, the coating underwent local exfoliations, but intact areas still preserved superhydrophobicity. In photobiologically active seawater, on samples without the superhydrophobic coating (controls) pitting was inhibited, probably due to the adsorption of organic compounds produced by the photobiological activity. After 3 weeks of immersion, the surface of the coating became hydrophilic due to diatom coverage. As suggested by intermediate observations, the surface below the diatom layer is suspected of having lost its superhydrophobicity due to early stages of biofouling processes (organic molecule adsorption and diatom attachment/gliding). Polarization curves also revealed that the metal below the coating underwent corrosion inhibiting phenomena as observed in controls, likely due to the permeation of organic molecules through the coating. Hence, the initial biofouling stages (days) occurring in photobiologically active seawater can both accelerate the loss of superhydrophobicity of coatings and promote corrosion inhibition on the underlying metal. Finally, time durability of superhydrophobic surfaces in real seawater still remains the main challenge for applications, where the early stages of immersion are demonstrated to be of crucial importance., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Highly hydro and oleophobic materials applied to needs of the marine environment represent a relatively young field achieving growing interest as innovative solution, where technological and ecological aspects allow to be merged, taking into account the limitations imposed by international laws in terms of environmental protection. In this work a superhydrophobic (SH) coating for seawater applications has been characterized and tested in both laboratory and field conditions, since investigations in real seawater are crucial to evaluate the behaviour of SH surfaces because of a complexity not reproducible in laboratory. Taking into account the real conditions where the surface can operate oleophobicity can be investigated in presence of organic and inorganic pollution. The amphiphobic surface has been also studied to simulate those applications where the surface undergoes to thermal stress like pipelines and desalination plants affected by biofouling. The preliminary wearing test shows the effective resistance to a continuous low velocity impact of micrometric particles of the coating investigated here. Finally, time durability in field tests has been studied as a function of immersion angle in real seawater environment to investigate the role of the coating on early stages of biofilm growth. [ABSTRACT FROM AUTHOR]

Highly water repellent coatings known as superhydrophobic (SH) are related to surfaces with contact angles above 150° and a very small hysteresis. Among many practical needs to which this property can be devoted, a very interesting field where the SH coating technology can be employed is represented by the protection of hulls in seawater environments from the biofouling colonization. The absence of toxic materials in the final product and in the preparation stage holds to preferable bio-compatible coatings, basing the action on low surface energy exerting physical prevention of bioadhesion of colonizing organisms. In this work we report on field tests of a superhydrophobic ‘green’ coating on aluminum and glass substrates in real seawater mesocosms conditioned/not conditioned by the natural photoperiod and the photobiology development. In particular, the performance, durability and fouling removability of the here tested SH coating is evaluated with immersions focusing on two time scales (days and weeks), emphasizing the role of conditioning film and initial biological slimes formation. Implications of results here obtained on ship hulls protection and indications for future investigations to be held are discussed. [ABSTRACT FROM AUTHOR]