The Release Behavior of Silicone Coatings With a Thickness Gradient

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Engineering | Materials Science and Engineering


Silicone coatings are being investigated for their foul release properties and durability in application to prevent fouling on ship hulls. To date, studies have focused on coatings with uniform thickness. These studies have shown that their release behavior follow a model presented by Kendall (1971). In that, the force required to remove pseudobarnacles, modeled as epoxy studs, from thin silicone coatings decreases as the thickness increases. The two types of release mechanisms observed were void formation and edge peeling.

However, coatings on ships’ hulls may contain areas where the coating is not uniform but may have a wavy pattern to it. In the present study, pull-off tests were performed in order to study the release behavior of epoxy from clear silicone coatings with a thickness gradient on glass substrates. The four types of release behavior observed were void formation, peeling, mixed mode of void formation then peeling, and mixed mode of fingering then peeling. The type of mixed mode release was dependent on the average thickness and thickness gradient. For samples undergoing mixed mode release, the thinner coatings had small multiple void formations, whereas the thicker coatings had a fingering decohesion pattern near the edge before peeling. For most of the samples tested, separation of the epoxy from the coating started mostly on the thin side of the coating and then proceeded to the thick side. An equivalence length parameter was also introduced that distinguishes the three modes of release involving peeling.