Structures and antifouling properties of low surface energy non-toxic antifouling coatings modified by nano-SiO_2 powder

Antifouling coatings are used to improve the speed and energy efficiency of ships by preventing or- ganisms, such as barnacles and weed, building up on the underwater hull and helping the ships movement through the water. Typically, marine coatings are tributyltin self-polishing copolymer paints containing toxic molecules called biocides. They have been the most successful in combating bio- fouling on ships, but their widespread use has caused severe pollution in the marine ecosystem. The low surface energy marine coating is an entirely non-toxic alternative, which reduces the adhesion strength of marine organisms, facilitating their hydrodynamic removal at high speeds. In this paper, the novel low surface energy non-toxic marine antifouling coatings were prepared with modified acrylic resin, nano-SiO2, and other pigments. The effects of nano-SiO2 on the surface structure and elastic modulus of coating films have been studied, and the seawater test has been carried out in the Dalian Bay. The results showed that micro-nano layered structures on the coating films and the lowest surface energy and elastic modulus could be obtained when an appropriate mass ratio of resin, nano-SiO2, and other pigments in coatings approached. The seawater exposure test has shown that the lower the sur- face energy and elastic modulus of coatings are, the less the marine biofouling adheres on the coating films.     

海洋污损生物粘附机制及防污涂层表面工程

任何浸入海水的结构物均会受到海洋污损生物的附着。 在物体表面涂覆防污涂料是最广泛的防污方式,无毒污损脱附型防污涂料已成为当前的研究热点。 分析了污损生物的粘附过程及界面粘结作用,探讨了表面能、涂层模量、表面化学成分、微观形貌、颜色等因素对涂层防污效果的影响,并指出涂料工程化中必须解决的问题。     

Preparation of acrylic resin/modified nano-SiO<Subscript>2</Subscript> via sol-gel method for leather finishing agent

Acrylic resin/nano-SiO₂ (AR/nano-SiO₂) composite was prepared by physical blends of acrylic resin (AR) and nano-SiO₂, which was synthesized via the sol-gel method of tetraethoxysilane (TEOS) catalyzed with alkali. The synthetic conditions, such as surfactant type, the content of nano-SiO₂ sol, stirring speed, mixed temperature and ultrasonic treatment, on nanocomposites’ property were studied in detail. DSC indicated the glass transition temperature of AR/nano-SiO₂ (Tg = −26.7°C) was a little higher than that of the acrylic resin (Tg= −29.6°C). Water uptake confirmed that the water resistance of AR/nano-SiO₂ was improved by 55.94% and the solvent resistance by 54.79% when compared with AR. The improved properties of leather finished by AR/nano-SiO₂ were shown, in contrast to AR treatment; water vapor permeability was increased by 9.15% and the finish adhesion by 10.35%.     

Contact angle hysteresis, adhesion, and marine biofouling

Adhesive and marine biofouling release properties of coatings containing surface-oriented perfluoroalkyl groups were investigated. These coatings were prepared by cross-linking a copolymer of 1H,1H,2H,2H-heptadecafluorodecyl acrylate and acrylic acid with a copolymer of poly(2-isopropenyl-2-oxazoline) and methyl methacrylate at different molar ratios. The relationships between contact angle, contact angle hysteresis, adhesion, and marine biofouling were studied. Adhesion was determined by peel tests using pressure-sensitive adhesives. The chemical nature of the surfaces was studied by using X-ray photoelectron spectroscopy. Resistance to marine biofouling of an optimized coating was studied by immersion in seawater and compared to previous, less optimized coatings. The adhesive release properties of the coatings did not correlate well with the surface energies of the coatings estimated from the static and advancing contact angles nor with the amount of fluorine present on the surface. The adhesive properties of the surfaces, however, show a correlation with water receding contact angles and contact angle hysteresis (or wetting hysteresis) resulting from surface penetration and surface reconstruction. Coatings having the best release properties had both the highest cross-link density and the lowest contact angle hysteresis. An optimized coating exhibited unprecedented resistance to marine biofouling. Water contact angle hysteresis appears to correlate with marine biofouling resistance.     

RuO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript> mixed oxide composite coating for improvement of Al-alloy sacrificial anodes

It has been recently proved that RuO₂ can act as an effective surface activator of aluminum alloy sacrificial anodes. TiO₂ has the property of stabilizing RuO₂ coating and resisting biofouling on metal surfaces. Hence, a mixed oxide catalytic coating of TiO₂ and RuO₂ can enhance the galvanic performance of aluminum alloy sacrificial anodes and resists biofouling on the anode surface. In the present work RuO₂–TiO₂ mixed oxide was coated on aluminum alloy sacrificial anodes. The large and uniform porous nature of the coating was found to facilitate efficient ion diffusion. The coating was found to persist on the anode even after 3 months of galvanic exposure. The anode having an optimum combination of the mixed oxide had 70% TiO₂ as the major component in the coating. The catalytic coating significantly improved the performance of the anodes to a large extent.     

水性防污涂料的研究进展

海洋污损生物是海洋资源开发首先要面对的问题。防污涂料是防除海洋污损生物的关键材料。传统的防污涂料虽然发展成熟,但以油性溶剂为介质,存在挥发性有机物(VOC)排放过高、环境污染严重的问题。不释放VOC的水性涂料符合绿色无污染的环保要求,是防污材料领域研究的热点。本文对最重要的四种水性防污涂料(污损释放型水性低表面能防污涂料、自抛光型水性防污涂料、污损阻抗型水凝胶海洋防污涂料、强碱释放型水性硅酸盐防污涂料)从防污机理、制备方法和存在的问题等几个方面进行了综述,并对水性防污涂料的发展趋势进行了展望。     

Development of multifunctional polydimethylsiloxane (PDMS)‐epoxy‐zinc oxide nanocomposite coatings for marine applications

Multifunctional epoxy‐polydimethylsiloxane nanocomposite coatings with antifouling and anticorrosion characteristics have been developed via in situ polymerization method at different loading (1, 3, and 6.5 wt.%) of ZnO nanoparticles to cater marine applications. A detailed comparative analysis has been carried out between epoxy‐polydimethylsiloxane control (EPC) and ZnO‐reinforced coatings to determine the influence of ZnO loading on various properties. The incorporation of ZnO in EPC led to increase in root mean square (RMS) roughness to 126.75 nm and improved hydrophobicity showing maximum contact angle of 123.5° with low surface energy of 19.75 mN/m of nanocomposite coating as compared with control coating. The differential scanning calorimetry (DSC) result indicated improved glass transition temperature of nanocomposite coatings with highest T_g obtained at 83.69°C in case of 1 wt.% loading of ZnO. The increase in hydrophobicity of the system was accompanied by upgraded anticorrosion performance exhibiting 98.8% corrosion inhibition efficiency (CIE) as compared with control coating and lower corrosion rate of 0.12 × 10^?3 mm/year. The Taber abrasion resistance and pull‐off adhesion strength results indicated an increment of 34.7% and 150.7%, respectively, in case of nanocomposite coating as compared with the control coating. The hardness of nanocomposite coatings was also improved, and maximum hardness was found to be 65.75 MPa for nanocomposite coating with 1 wt.% of ZnO. Our study showed that the nanocomposite coating was efficient in inhibiting accumulation of marine bacteria and preventing biofouling for more than 8 months. The developed environment‐friendly and efficient nanocomposite material has a promising future as a high‐performance anticorrosive and antifouling coating for marine applications.     

Dynamical Mechanical Analysis and Curing Analysis of Fouling Release Coatings and Components

A commercially available fouling release (adsorbed foulants removed by shear flow) coating based on poly(dimethylsiloxane) and a commercial marine epoxy primer have been analyzed by diffusing wave spectroscopy and by thermal and dynamical mechanical methods. Diffusing wave spectroscopy reveals 7–9 distinct relaxation intervals over short (minutes) to long (20 hour) time scales. Several junctures of these intervals are shown to correlate with mechanically determined film formation parameters, such as set to touch times, tack free times, and dry through times. Thickness series of coatings made by casting illustrate similarities and distinct differences between the epoxy primer and poly(dimethylsiloxane)-based fouling release coating formulations. Several low temperature β transitions are resolved in the fouling release coatings in addition the α (T_g) transition in both formulations. A scaling analysis of the thickness series data shows that both the primer and the top coat exhibit a negative exponent for thickness; −0.77 for the epoxy; −1.2 for the top coat. Stress-strain experiments reveal further significant difference between these two types of elastomers. The elastic modulus for the epoxy is 1000-fold higher than for the topcoat. A small elastic modulus is thought to be key in the successful functioning of fouling release coatings. Analyses of substrate effects (wire mesh, fiberglass braid) and of coating or loading levels on dynamical mechanical properties, in comparison with thickness series of thin films are presented. The woven braid offers the advantage that it can be loaded more easily than can wire mesh substrates. The negative exponents show that thinner coatings may be more mechanically resilient than thicker coatings, as the ability to store and dissipate mechanical energy decreases as thickness increases.     

Low-temperature processing of sol-gel derived Pb(Zr,Ti)O<Subscript>3</Subscript> thick films using CO<Subscript>2</Subscript> laser annealing

Fabrication of ferroelectric Pb(Zr_0.52Ti_0.48)O₃ (PZT) thick films on a Pt/Ti/SiO₂/Si substrate using powder-mixing sol-gel spin coating and continuous wave CO₂ laser annealing technique to treat the specimens with at a relatively low temperature was investigated in the present work. PZT fine powders were prepared by drying and pyrolysis of sol-gel solutions and calcined at temperatures from 400 to 750°C. After fine powder-containing sol-gel solutions were spin-coated on a substrate and pyrolyzed, CO₂ laser annealing was carried out to heat treat the specimens. The results show that laser annealing provides an extremely efficient way to crystallize the materials, but an amorphous phase may also form in the case of overheating. Thicker films absorb laser energy more effectively and therefore melt at shorter periods, implying a significant volume effect. A film with thickness of 1 μm shows cracks and rough surface morphology and it was difficult to obtain acceptable electrical properties, indicating importance of controlling interfacial stress and choosing appropriate size of the mixing powders. On the other hand, a thick film of 5 μm annealed at 100 W/cm² for 15 s exhibits excellent properties (P _r = 36.1 μC/cm², E _c = 19.66 kV/cm). Films of 10 μm form a melting zone at the surface and a non-crystallized bottom layer easily at an energy density of 100 W/cm², showing poor electrical properties. Besides, porosity and electrical properties of thick films can be controlled using appropriate processing parameters, suggesting that CO₂ laser annealing of modified sol-gel films is suitable for fabricating films of low dielectric constants and high crystallinity.     

Electrocatalytic activity of hemoglobin in sodium alginate/SiO<Subscript>2</Subscript> nanoparticle/ionic liquid BMIMPF<Subscript>6</Subscript> composite film

A novel biocompatible composite film containing sodium alginate (SA), room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF₆), SiO₂ nanoparticle, and hemoglobin (Hb) was fabricated and covered on the surface of a traditional carbon paste elecrode (CPE). The immobilized Hb on the electrode surface showed good direct electrochemical behaviors, and a pair of quasi-reversible redox peaks of Hb was obtained, which indicated that the direct electron transfer of Hb with the electrode surface had been achieved. The SA/nano-SiO₂/BMIMPF₆/Hb/CPE showed dramatically electrocatalytic activity to the reduction of trichloroacetic acid, hydrogen peroxide (H₂O₂), and oxygen (O₂). The kinetic parameters for the electrocatalytic reactions were evaluated. The composite film showed the potential to the biosensor and biocatalysis.     

Study on parylene/SiO<Subscript>2</Subscript> composite films for protection of KDP crystals

In this paper, parylene/SiO₂ composite films were reported to protect KDP crystals, indispensable cells in ICF experiments, from moisture. FTIR, UV-NIR spectra and XPS were used to analyze the properties of films. Laser damage threshold of films was also measured. With porous silica coating on surface of parylene film, the transmittance of dual layers can be raised to more than 91%. KDP crystals with poly(p-xylylene)/SiO₂ coating could work well in ambient atmosphere for more than half a year.     

原位探测防污高分子材料与液体界面的分子结构

Marine organisms such as plants, algae or small animals can adhere to surfaces of materials that are submerged in ocean. The accumulation of these organisms on surfaces is a marine biofouling process that has considerable adverse effects. Marine biofouling on ship hulls can cause severe fuel consumption increase. Investigations on antifouling polymers are therefore becoming important research topics for marine vessel operations. Antifouling polymers can be applied as coating layers on the ship hull, protecting it against the settlement and growth of sea organisms. Polyethylene glycol (PEG) is a hydrophilic polymer that can effectively resist the accumulation of marine organisms. PEG-based antifouling coatings have therefore been extensively researched and developed. However, the inferior stability of PEG makes it subject to degradation, rendering it ineffective for long-term services. Zwitterionic polymers have also emerged as promising antifouling materials in recent years. These polymers consist of both positively charged and negatively charged functional groups. Various zwitterionic polymers have been demonstrated to exhibit exceptional antifouling properties. Previously, surface characterizations of zwitterionic polymers have revealed that strong surface hydration is critical for their antifouling properties. In addition to these hydrophilic polymers, amphiphilic materials have also been developed as potential antifouling coatings. Both hydrophobic and hydrophilic functional groups are incorporated into the backbones or sidechains of these polymers. It has been demonstrated that the antifouling performance can be enhanced by precisely controlling the sequence of the hydrophobic-hydrophilic functionalities. Since biofouling generally occurs at the outer surface of the coatings, the antifouling properties of these coatings are closely related to their surface characteristics in water. Therefore, understanding of the surface molecular structures of antifouling materials is imperative for their future developments. In this review, we will summarize our recent advancements of antifouling material surface analysis using sum frequency generation (SFG) vibrational spectroscopy. SFG is a surface-sensitive technique which can provide molecular information of water and polymer structures at interfaces in situ in real time. The antifouling polymers we will review include zwitterionic polymer brushes, mixed charged polymers, and amphiphilic polypeptoids. Interfacial hydration studies of these polymers by SFG will be presented. The salt effect on antifouling polymer surface hydration will also be discussed. In addition, the interactions between antifouling materials and protein molecules as well as algae will be reviewed. The above research clearly established strong correlations between strong surface hydration and good antifouling properties. It also demonstrated that SFG is a powerful technique to provide molecular level understanding of polymer antifouling mechanisms.     

Tantalum oxide effect on the surface structure and morphology of the IrO<Subscript>2</Subscript> and IrO<Subscript>2</Subscript> + RuO<Subscript>2</Subscript> + TiO<Subscript>2</Subscript> coatings and on the corrosion and electrochemical properties of anodes prepared from these

Alterations in the phase composition, porosity, and surface morphology of coatings are examined following the insertion of a quantity of Ta₂O₅ into active coatings prepared from IrO₂ or IrO₂ + RuO₂ + TiO₂ (OIRTA). It is shown that even an insignificant concentration of Ta₂O₅ in a coating renders it substantially amorphous and leads to the appearance of a large number of wide protracted cracks in the coating. The latter extends the surface of anodes and boosts their apparent catalytic activity in the chlorine evolution reaction. In addition, this accelerates the diffusion of chloride ions toward the front surface of anodes, which noticeably reduces the overvoltage of the chlorine evolution reaction when manufacturing sodium chlorate. The coatings’ amorphization and the development of their surface substantially reduce the corrosion resistance of these anodes as compared with OIRTA.     

Effect of acrylic polymer and nanocomposite with nano-SiO2 on thermal degradation and fire resistance of APP-DPER-MEL coating

Acrylic nanocomposite and flame retardant coatings with different acrylic polymers were prepared. The effect of molecular structure and molecular weight of acrylic resins and nanocomposite with nano-SiO₂ on the interaction and char formation of ammonium polyphosphate-dipentaerythritol-melamine (APP-DPER-MEL) coating was investigated using differential thermal analysis (DTA), thermogravimetry (TG), Limiting Oxygen Index (LOI), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and fire protection test. The interaction of APP, DPER, MEL and 3F-1 acrylic resin led to the formation of intumescent coherent char at 300-450 °C. Owing to low molecular weight and lack of benzene rings, F-963 acrylic resin decomposed at lower temperature than APP, and hence their endothermic interaction was destroyed. The well-distributed nano-SiO₂ particles in acrylic nanocomposite could modify char formation and anti-oxidation of char structure at high temperature. It is noted that the fire protection properties of nanocoating with acrylic nanocomposite were better than those of flame retardant coatings with conventional acrylic resins.     

Thermal preparation and stabilization of crystalline silver particles in SiO<Subscript>2</Subscript>-based coating solutions

Ag/SiO₂ coating solutions for antimicrobial functionalisation can be prepared by a thermal reaction (reflux or solvothermal conditions) of mixtures of tetraethoxysilane, alkylamine compounds and AgNO₃. These coating solutions are especially useful for antimicrobial refinement of temperature sensitive materials like textiles or wood. Moreover coating application onto substrates such as glass or metal, as well as preparation of micrometer sized bulk particles by using a spray-drying process is also feasible. The efficiencies of AgNO₃ reduction in the presence of different amine compounds like triethanolamine, triethylamine or diethanolamine are compared. SiO₂ nanoparticles are formed by basic hydrolysis of tetraethoxysilane and stabilize the crystalline silver particles in the solution. The antimicrobial effect of silver containing coatings on textile fabrics is investigated.     

Preparation and characterization of polyurethane based self-cleaning and antibacterial coating containing silver ion exchanged montmorillonite/TiO<Subscript>2</Subscript> nanocomposite

In order to reach an antibacterial, photocatalytic, and hydrophilic coating, commercial grade polyurethane (CPU) resin was modified with silver ion exchanged montmorillonite/TiO₂ nanocomposite in various montmorillonite to TiO₂ nanoparticle ratios. To characterize the prepared nanocomposites and coatings, X-ray diffraction patterns, FTIR and UV–Vis spectroscopy and SEM images were used. The modified commercial grade polyurethane coatings containing nanocomposites show better properties, including hydrophilicity, degradation of organic pollutants, antibacterial activity and water resistivity, compared to unmodified commercial grade polyurethane coatings. The water droplet contact angle of unmodified CPU coating was 70°, however it decreased to lower than 10° in modified CPU coatings after 24 h LED lamp irradiation. Decolorization efficiency of malachite green dye solution by the use of modified CPU coatings achieved up to 70% after 5 h LED lamp illumination, compared to less than 5% for unmodified CPU coatings. Modified CPU coatings also showed significant water resistivity and antibacterial properties.     

Elastic modulus profiles in the cross sections of drying alkyd coating films: modelling and experiments

The temporal development of the modulus of elasticity and its profile were studied in water-borne alkyd coatings during the drying process of the coating films. Values of the Young’s moduli of elasticity of free coating films were measured using tensile tests. Since the elastic modulus is related to cross-link density, the values of the moduli give information on the advancement of the drying process. A mathematical model was developed to predict the degree of effective cross-linking and the mechanical behaviour of the drying coating films with different thicknesses. This model is based on trends observed by confocal Raman microspectroscopy, which exhibit the profile of the consumption of double bonds and thus can be used to monitor the development of cross-link density as a function of depth from the film surface. The average values of the Young’s measured moduli were successfully described by the numerical model as a function of drying time.     

Quantum-chemical analysis and experimental synthesis of titanium-vanadium-containing coatings on the silica surface from a mixture of TiCl<Subscript>4</Subscript> and VOCl<Subscript>3</Subscript> vapors

A process for the synthesis of a two-component vanadium-titanium-containing monolayer coating on the silica surface by treating the latter with a mixture of TiCl₄ and VOCl₃ vapors was considered. Quantum-chemical simulations showed that the synthesis temperature and concentrations of the reactants in the gas phase have a decisive influence on the composition and structure of the resulting coating. Based on the model predictions, two-component coatings with 0.2–0.9 ratios of the molar concentration of vanadium to that of titanium in the solid phase were synthesized. The ratio of the content of the solid-phase vanadium to titanium was shown to linearly vary with the VOCl₃ to TiCl₄ concentration ratio in the vapor mixture over wide temperature and concentration ranges, which allows controlling the composition of the two-component coatings being formed.     

Soluble Powders as Precursors for TiO<Subscript>2</Subscript> Thin Films

Amorphous precursor powders have proven to be highly advantageous for the sol–gel processing of TiO₂ thin films. Oxide yield, density, solubility, and thermal degradation of powders prepared under various conditions were determined; the thermoanalytical data could be assigned to the oxidative decomposition of different organic constituents. Certain powders are suitable for the preparation of alcohol-based sols, whereas also aqueous coating solutions can be prepared from others. Thin films prepared from both systems show excellent adhesion and optical properties when deposited on borosilicate glass substrates.     

Effects of aging time on V2O5 sol-gel coatings

Vanadium pentoxide (V₂O₅) sols have been used in conductive coatings and related applications [1, 2, 3]; however, the changes which may occur in the properties of these coatings with sols of different ages have not been carefully shown. Properties which may be dependent on the age of the sol (sol viscosity, film morphology and conductance) were measured in this work. The coating sols were prepared by ion-exchange of sodium metavanadate solutions.It was found that the coating thickness, sol viscosity, and surface morphology of the coatings were directly related to the age of the sol used. The dried coating thickness increased from 3 microns to 20 microns over a 30 day period. The sol viscosity increased from 1 centipoise to near 2 centipoise. The surface morphology of the coatings changed from that of a featureless surface at day 1 to a continual coverage of micron-sized fibers as the coating sols aged. The conductivity of the coatings, though, was unaffected by the age of the sol. The coating properties were correlated to the amount of polymerization of dissolved precursors in solution.