ABSTRACT
Quick and reliable testing is crucial for the development of new fouling release (FR) coatings. Exposure of these coatings to natural multispecies communities is essential in evaluating their efficacy. To this end, we present a rotating disk setup for dynamic field exposure. To achieve a well-defined flow on the surface of the disk, an easy to use sample mounting system was developed that provides a smooth and even surface. We related the angular velocity of the disk to the wall shear stress on the surface with a hydrodynamic model. The wall shear stress was adjusted to values previously found to be suitable to discriminate dynamic diatom attachment on different coating chemistries in the lab. The effect of the dynamic conditions was shown by comparing polystyrene slides under static and dynamic exposure. Using a set of self-assembled monolayers, the discrimination potential of the assay in a multispecies environment was demonstrated.
Subject(s)
Biofilms , Biofouling , Diatoms/physiology , Hydrodynamics , Polystyrenes/chemistry , Surface PropertiesABSTRACT
Amphiphilic coatings are promising candidates for fouling-release applications. As hydrophilic components, polysaccharides are interesting and environmentally benign building blocks. We used covalently coupled alginic acid (AA) and hyaluronic acid (HA) and postmodified them with a hydrophobic fluorinated amine. The surfaces showed good stability under marine conditions and fluorination led to a decreased uptake of Ca(2+) ions after modification. In single species settlement assays (bacteria, diatoms, barnacle cypris larvae), the modification decreased the settlement density and/or the adhesion strength of many of the tested species. Field studies supported findings of the laboratory experiments, as hydrophobic modification of AA and HA decreased diatom colonization.
Subject(s)
Aquatic Organisms/physiology , Biofilms/drug effects , Biofouling/prevention & control , Surface-Active Agents/chemistry , Alginates/chemistry , Amines/chemistry , Animals , Aquatic Organisms/drug effects , Calcium/chemistry , Crustacea/drug effects , Crustacea/physiology , Diatoms/drug effects , Diatoms/physiology , Gammaproteobacteria/drug effects , Gammaproteobacteria/physiology , Glucuronic Acid/chemistry , Hexuronic Acids/chemistry , Hyaluronic Acid/chemistry , Hydrophobic and Hydrophilic Interactions , Surface-Active Agents/pharmacologyABSTRACT
Among the first events after immersion of surfaces in the ocean is surface 'conditioning'. Here, the accumulation and composition of the conditioning films formed after immersion in the ocean are analyzed. In order to account for different surface chemistries, five self-assembled monolayers that differ in resistance to microfouling and wettability were used. Water samples from two static immersion test sites along the east coast of Florida were collected at two different times of the year and used for experiments. Spectral ellipsometry revealed that conditioning films were formed within the first 24 h and contact angle goniometry showed that these films changed the wettability and rendered hydrophobic surfaces more hydrophilic and vice versa. Infrared reflection adsorption spectroscopy showed that the composition of the conditioning film depended on both the wettability and immersion site. Laboratory and field assays showed that the presence of a conditioning film did not markedly influence settlement of microorganisms.
Subject(s)
Aquatic Organisms/physiology , Biofilms/growth & development , Biofouling , Seawater/chemistry , Florida , Hydrophobic and Hydrophilic Interactions , Spectrophotometry, Infrared , Surface Properties , WettabilityABSTRACT
The contribution of biofilms to skin friction drag is not clearly defined, and as regulations continue to restrict the use of biocides in antifouling paints, they are likely to form a greater presence on ship hulls. This paper reviews the flow regime around a ship's hull, the basics of boundary layer structure, and the effects of rigid surface roughness on drag. A review of experimental studies of biofilms in turbulent shear flows at laboratory and ship-scale is made. The consensus of these studies shows that biofilms increase skin friction drag. Some measurements carried out in turbulent boundary layer flow using a two-component, laser Doppler velocimeter (LDV) are also presented. These results indicate an increase in skin friction for biofilms that is dependent on composition as well as thickness.
ABSTRACT
Field testing of non-toxic antifouling coatings has required the development of test protocols that can quantify their performance. This includes the evaluation of the biofouling communities, the measurement of biofouling adhesion using a calibrated water jet and the measurement of barnacle adhesion in shear. Data are presented for several test surfaces, and the results are discussed with respect to the coating characteristics.
