The surface properties of silicone elastomers Exposed to seawater

Abstract

The performances of some silicone elastomers as compliant coatings which are resistant to marine fouling have been assessed from a sea-water exposure trial covering three fouling seasons. Measurements of contact angles (polar and non-polar liquids, recently-advanced and recently-receded liquid drops and air bubbles) have been used to investigate the surface properties of materials and of coatings resistant to fouling after two years' exposure. The unmodified poly (dimethyIsiloxane) elastomer General Electric (GE) 21 was still resistant to marine settlement after three seasons and the poly(dimethyldiphenylsiloxane) GE655 only became fouled during the third season. No other unmodified material showed resistance to fouling beyond two seasons. The addition of a low-viscosity poly(dimethylsiloxane) oil to GE655 in a sufficient quantity (20 mass %) to cause blooming resulted in a material that remained free of fouling. Time-dependent behaviour by drops of all liquids on freshly prepared samples was observed in recently-advanced contact angles but not by recently-receded contact angles. With polar liquids, hard clear elastomers showed stepwise changes and also gave considerable contact-angle hysteresis effects. Immersion in water over a period of several weeks brought about a slow decrease in the hydrophobicity of all elastomers. GE21, after exposure in seawater for over two years, also showed a decrease as indicated by the contact angle of distilled water drops on its surface. The slow changes in the interfacial properties of silicones with polar liquids are attributed to rearrangements of polymer chains close to the surface, driven by the formation of hydrogen bonds between the solvent and oxygen atoms in the backbone. Penetration of the material by water gradually increases the surface energy and, sooner or later, the material becomes susceptible to fouling. For GE655, this may be delayed by incorporating with the formulation a relatively incompatible low-viscosity silicone oil.

The Effect of Gregariousness in Cyprid Settlement Assays

“…In this context in vitro settlement assays can only provide information for preliminary screening. Antifouling research programmes should also incorporate multi-species in vitro assays (Butler et al, 1996), and field trials based on traditional immersion studies (Nevell et al, 1996), or analysis of larval exploratory behaviour (Thomason et al, 2002).…”

Interspecific variation in patterns of adhesion of marine fouling to silicone surfaces

“…The critical surface tensions of silicones and other materials change over time with immersion (Meyer et al 1988;Nevell et al 1996). Hydrophobic silicone substrata become more hydrophilic due to rearrangement of polymer chains at the material surface with penetration of water (Nevell et al 1996).…”

Polymers for Combating Biocorrosion

“…Silicones are composed of a variety of organic-inorganic hybrid materials, which have been widely considered as alternative to replace chromate ion coatings for corrosion inhibition (Brady, 1999). Due to their low elastic modulus resulting from a flexible, inorganic -Si-O backbone linkage and a critical surface tension as derived from the alkyl side chains, silicones have been extensively employed as fouling-release coatings (Edwards et al, 1994;Nevell et al, 1996;Watermann et al, 1997;Brady and Singer, 2000;Estarlich et al, 2000;Kus et al, 2005). Moreover, silicones have also been reported to possess a good corrosion protection ability (Gu et al, 1998b).…”