RIASSUNTO
ABSTRACT
The attachment of marine fouling organisms is harmful to any marine structure such as ship hulls, fishing nets, jetties and platforms. The surface microstructure of materials has a great influence on its antifouling performance. The authors' previous study states that shells are a better choice as biomimetic drag reducing objects than sharks since the living condition of shells is very close to the condition of ship fouling occurrence. Researches into shell surface topographies often concentrate on shells with rib-like structures. But the riblet structures' antifouling mechanism is not yet known for us. It's clear that the effects of surface structures are related to the scale of fouling organisms. There have been promising results that any single size of riblet structure can't prevent the most species of fouling organisms and the defense effect diminishes with time. Because of the gradually changing structures of the shell surface, it's hard to evaluate the shell surface morphologies. The aim of this study is to develop a new characterization system of shell surfaces and analyze the correlation between surface morphologies and antifouling properties in order to fabricate biomimetic surfaces. In order to define the three-dimensional surface feature of shells, a new kind of method for characterizing the geometric model of shell surface was developed to describe the two-dimensional and three-dimensional surface characterizations. A great number of experiments were conducted to obtain the texture characteristics of antifouling shell surfaces based on statistical analysis. The correlation between surface morphologies and antifouling properties was analyzed and the assessment system was also proved reliable.
INTRODUCTION
The marine fouling organisms have seriously affected the marine transport for many years. Their attachment on ship hulls not only increases fuel consumption, but also enhances the hull erosion so as to decrease the ship economy and safety. In addition, the transportation along with ships from one area to another area can be considered as biological invasion from an ecological point. The traditional antifouling methods are using toxic coatings, which have gradually been forbidden because of the bad impact on the marine environment. Therefore developing new kinds of environmentally friendly antifouling methods is receiving much attention in the marine antifouling field [Wahl, 1998; Scardino, 2010]. The surface microstructural antifouling is put forward recently based on biomimetics. The phenomena that some kinds of marine creatures such as sharks, dolphins and shells can live in the marine environment without fouling are observed by scientists. That means these creatures have selfcleaning systems. Nowadays many studies can prove that these marine creatures' surfaces are not smooth but micro-structural and the surface micro topographies play an important role in their antifouling systems. Nature has developed materials, objects, and processes that function from macro scale to nano scale for thousands of years [Bhushan, 2009]. Natures' phenomena can provide great inspirations to humans and vital ideas for many revolutionary developments. For instance, the radar was invented by studying bat's echolocation system and the plane flies like birds with wings opening in the sky. Biomimetic, meaning to mimic biology, involves the understanding of biological functions, structures, principles of various objects found in nature, and the design of various devices inspired from the nature [Bhushan, 2010; Dean, 2010]. Then scientists get antifouling topographies by studies of surfaces of marine creatures. The ideal antifouling technology should be non-toxic and without biocides. So the bionic antifouling technique of surface micro topographies shows a good future.