Development Of New Coatings And Technologies Against Marine Biofouling

This thesis focuses on the development of new coatings and technologies againstmarine biofouling. We have tried to develop three different kind of polymeric coatings:water-filled porous elastomers, coatings with a self-generating hydrogel surface andcoatings with self-generating and renewing micro-patterned surface.First, we have prepared a new kind of coatings by mixing silicone with a cross-linkable functional group, sodium chloride powders, dispersing agent and medium(solvent). The sodium chloride was first grinded into tiny crystals (2~10m) by using aplanetary ball mill before dispersing into the mixture. After adding the cross-linkingagent and stirring, the mixtures were coated on testing surface. We used a range ofexperimental methods, including SEM, rotational rheometer, pseudo-barnacle adhesionand contact angle, to study the surface character, structure, shear storage modulus andfouling-release ability. The SEM images revealed that small NaCl crystals wereuniformity dispersed inside each coating before its immersion in sea water and theformation of a water-filling porous structure due to the dissolution of NaCl salts. Ourmeasurements showed that there is a little change in surface energy, similar to that ofsilicone elastomers if the dispersing agent and NaCl were added or immersed in seawater. The rheology measurements showed that the existence of many micro-drops ofwater in this kind of specially designed elastomers decreases their shear storagemodulus. The decrease of shear modulus of a coating plays a leading role infouling-release because it is directly linked to a lower critical stress of peeling-off apseudo-barnacle on its surface. The addition of more NaCl salts leads to a betterfouling-release property.Secord, we have synthesized a set of copolymers with a carboxyl pendant group andtri-butyl-silyl-ester group. The solution of this kind of copolymers was mixed withpolyfunctional aziridine cross-linker before forming a thin film (coating). The changesof structure, water-adsorption and surface character of each coating after its immersionin sea-water have been investigated by using scanning electron microscope (SEM),Fourier transform attenuated total reflection infrared spectrometry (ATR- FTIR),contact angle and weighting measurements. The fouling-resistant properties of panelscoated with different thin films were hanged and tested in a shallow sea. The ATR-FTIR measurements showed that after immersion in seawater carboxylic acids(anions) were gradually formed on surface that contacted with sea water because ofgradual hydrolysis of the tri-butyl-silyl-ester pendant group. The contact angle testsdemonstrated that the surface of each coating changed from hydrophobic to hydrophilicand the final hydrophilicity of the surface increases with the content of thetri-butyl-silyl-ester pendant groups. As expected. The water adsorption is correlated tothe hydrolysis of tri-butyl-silyl-ester pendant group; namely, the longer time the coatingis immersed in seawater, the more water it adsorbed, so that the hydrogel layer formedon surface becomes thicker and thicker. The SEM measurements also showed theself-peeling of these hydrogel layers, which was further confirmed by the weightchange of each coating after its immersion in sea water for different times. The hangingpanel tests in shallow sea showed that after two months these self-generating andself-peeling hydrogel layer coatings have a much better fouling-resistant ability thanthose non-cross-linked control coatings and the fouling-resistant ability increases withthe tri-butyl-silyl-ester pendant group content.Third, we first synthesized copolymers made of methyl methacrylate and butylacrylate-acrylic acid by continuously adding monomers in radical polymerization.These copolymers were further used as a dispersing agent to prepare dispersions with ahigh solid content (~21%) of acrylamide-acryl acid microgels with a diameter of 500nm. The diameter and solid content of the resultant microgel dispersion weredetermined by SEM and weighting. The copper self-polishing copolymer resins werefurther synthesized using the synthesized copolymer and mixed with microgels beforecoated on each testing surface. The SEM measurements revealed that the microgels areuniformly dispersed inside each coating. The dissociation of these surface microgelsfrom the coatings after its immersion in seawater for few weeks results in a porous andself- polishing surface. The dissociation rate was measured by weighting before andafter its immersion in sea water for a certain time period. We found that theself-polishing speed increases with the microgel content. The hanging panel test in ashallow sea showed that such a structured surface itself is not sufficient to resistbiofouling.