Fouling Release Research Articles

Self-growing composite photocatalytic materials for surface self-renewal of marine antifouling coatings

The attachment of marine organisms leads to the problem of marine biofouling. Biofouling can be prevented by using antifouling coatings this provided a low surface energy surface to inhibit the attachment of marine organisms. However, microorganisms inevitably attach during their use, leading to failure of the fouling release coating. To address this problem, we report an innovative strategy of doping photocatalytic materials into silicone coatings. This approach enables the degradation of bacterial carcasses and their secretions, leading to surface self-renewal and extended fouling protection. In this work, we report the controlled crystallisation of Ag-TiO2 nanomaterials (APTES-Ag@TiO2) using various methods influenced by aminopropylsilane. This strategy ensures the full utilisation of sunlight and strong interfacial adhesion, thereby preventing the degradation of photocatalytic performance. APTES-Ag@TiO2 not only has a self-growth effect and excellent photocatalytic performance but also facilitates the degradation of bacterial carcasses, thereby renewing the surface in organosilicon coatings.

Fouling Release Mechanism of an Octopus‐Inspired Smart Skin

AbstractThis work proposes an octopus‐inspired smart skin for fouling release. The skin consists of twisted spiral artificial muscles (TSAMs) embedded between two layers of elastomer. Upon electro‐thermal actuation, TSAMs undergo vertical displacement (similarly to octopus’ papillae dermal muscles) and mechanically deform the top layer of the skin where the biofilm is attached. The release is achieved by generating a critical strain on the skin's top layer. In this paper, a physics‐based mechanical model is proposed to describe the fouling release mechanism of the smart skin. The model relates the critical strain to the mechanical properties of the biofilm, as well as the mechanical and electro‐thermal properties of the TSAMs. The model is experimentally validated, and a robust controller is implemented to achieve the desired critical strain and then perform release for two different types of biofilms: bacterial‐based Escherichia coli and diatom‐based Amphora coffeaeformis.

Development of a mechanically robust silicon-based cross-linking polymer for the sustainable marine antifouling coatings

Silicone-based fouling release coatings (FRCs) have shown great promise as an environmentally friendly antifouling technology, while inferior mechanical properties and insufficient substrate adhesion have hindered their further application. We focused on enhancing the mechanical robustness of silicone-based coating through the synergistic effects of hydrogen bonding, π-π aromatic interaction and covalent bonding. The resulting silicone-based coating displayed a low surface energy of 23 mJ/m2 and improved mechanical strength and substrate adhesion, offering values up to 6.4 MPa (9.1 times higher) and 2.87 MPa (25.7 times higher), respectively. Additionally, the modified coating demonstrated a tear strength of 9.8 kN/m and mass loss only about 30 mg after enduring 10,000 wear cycles. Alkoxysilane-functionalized polyethylene glycol and quaternary ammonium salt were grafted into the cross-linking structure to make them anchored to the networks and migrated to the surface layer in seawater without releasing. The coating provided 99.1% antibacterial efficiency and effective antidiatom performance (≤ 11.2 cell/mm2). After a 12-month marine field test, the developed film showed only 20% micro bio-fouling compared to 100% fouling coverage on the PDMS surface. By combining improved mechanical properties with antifouling characteristics, this new multifunctional silicone-based FRC exhibits tremendous potential for sustainable marine antifouling coating application.

Bioinspired Zwitterionic Nanowires with Simultaneous Biofouling Reduction and Release.

Marine biofouling is a complex and dynamic process that significantly increases the carbon emissions from the maritime industry by increasing drag losses. However, there are no existing non-toxic marine paints that can achieve both effective fouling reduction and efficient fouling release. Inspired by antifouling strategies in nature, herein, a superoleophobic zwitterionic nanowire coating with a nanostructured hydration layer is introduced, which exhibits simultaneous fouling reduction and release performance. The zwitterionic nanowires demonstrate >25% improvement in fouling reduction compared to state-of-the-art antifouling nanostructures, and four times higher fouling-release compared to conventional zwitterionic coatings. Fouling release is successfully achieved under a wall shear force that is four orders of magnitude lower than regular water jet cleaning. The mechanism of this simultaneous fouling reduction and release behavior is explored, and it is found that a combination of 1) a mechanical biocidal effect from the nanowire geometry, and 2) low interfacial adhesion resulting from the nanostructured hydration layer, are the major contributing factors. These findings provide insights into the design of nanostructured coatings with simultaneous fouling reduction and release. The newly established synthesis procedure for the zwitterionic nanowires opens new pathways for implementation as antifouling coatings in the maritime industry and biomedical devices.

Carp-inspired self-regulating marine antifouling coating: Featuring robust controlled release of eugenol and high-efficiency self-healing performance

The practical application of low surface energy polydimethylsiloxane (PDMS) in marine antifouling is significantly limited due to its inadequate static antifouling capability. Herein, integrating a strategy inspired by carps to release antifouling agents with the fouling release properties of low surface energy materials, an innovative self-regulating marine antifouling coating (named PDMS-Pun-x) was developed, which demonstrates remarkable robust ability of controlled release of eugenol and efficient self-healing performance. Under seawater, the coating regulates its inherent hydrophilicity and the content of the surface anti-fouling agent to obtain the ability of controlled releasing eugenol. Compared with other self-renewal coatings, there proves non-heavy metal leaching and no internal self-hydrolysis existing. Moreover, based on the synergistic action of disulfide bonds and hydrogen bonds, the coating demonstrated a notable self-healing performance, with a self-healing rate of 94.06%. Additionally, the substrate of PDMS modified with polyurea provides the coating with excellent resistance against corrosion. This study introduces a highly promising approach towards the advancement of environmentally-friendly and durable marine antifouling coatings.

Hierarchical biocide-free silicone/graphene-silicon carbide nanocomposite coatings for marine antifouling and superhydrophobicity of ship hulls

A new series of fluorine-free, nonbiocidal, and hierarchical superhydrophobic silicone coatings filled with reduced graphene oxide (RGO)/β-SiC bamboo-like nanocomposites was successfully fabricated as durable ternary marine fouling release (FR) surfaces. RGO/β-SiC hybrid was used as coating nanofiller that would release fouling and confer surface robustness. It was facilely created using a straightforward one-phase ultrasonication technique. The dispersion of different concentrations of RGO sheets decorated with β-SiC bamboo-like fillers was determined to study the superhydrophobicity and antifouling behaviors of polysiloxane nanocomposites. RGO was prepared through a simple hydrothermal technique. Solution casting was used to distribute the RGO/β-SiC nanofillers throughout a silicone matrix. Atomic force microscopy, surface free energy, and water contact angle (WCA) were employed to examine the superhydrophobicity and micro/nanoroughness of the coatings. The mechanical, anticorrosive, and durability characteristics of the silicone-RGO/β-SiC-filled composites were also investigated. The antifouling effects of the coating systems were evaluated in the laboratory for 30 days with specific bacteria. The silicone-RGO/β-SiC (3 wt%) composite with the best dispersion, highest WCA (156°), and lowest surface free energy (12.7 mN/m) among the composites exhibited favorable FR characteristics. The well-dispersed PDMS-RGO/β-SiC (3 wt% nanofiller) composite presented the minimum degradation and cell viability percentages against Gram-positive and Gram-negative bacteria as well as diatoms. Therefore, this study produced a series of nonstick and fluorine-free ternary FR nanocomposites for maritime coatings with surface durability, superhydrophobicity, and fouling retardancy. This work highlights the design and preparation of multifunctional marine nanocoatings with excellent antifouling performance, easy applicability, and superhydrophobicity properties.

Impact of Molecular Weight on Anti-Bioadhesion Efficiency of PDMS-Based Coatings

Silicone elastomer coatings have shown successful fouling release ability in recent years. To further enhance the design of silicone coatings, it is necessary to fully understand the mechanisms that contribute to their performance. The objective of this study was to examine the relationship between the molecular weight of polydimethylsiloxane (PDMS) and antibioadhesion efficiency. PDMS-based coatings were prepared via a condensation reaction, with a controlled molecular weight ranging from 0.8 to 10 kg·mol−1. To evaluate changes in surface wettability and morphology, contact angle experiments and atomic force microscopy (AFM) were performed. Finally, the antibioadhesion and self-cleaning performance of PDMS coatings was carried out during in situ immersion in Lorient harbor for 12 months. Despite small variations in surface properties depending on the molecular weight, strong differences in the antibioadhesion performance were observed. According to the results, the best antibioadhesion efficiency was obtained for coatings with an Mn between 2 and 4 kg·mol−1 after 12 months. This paper provides for the first time the impact of the molecular weight of PDMS on antibioadhesion efficiency in a real marine environment.

Molecular structure design of polybenzoxazines with low surface energy and low modulus for marine antifouling application

The antifouling mechanism of low surface energy marine antifouling coatings is fouling release, and the key to fouling release is the adhesion strength of fouling organisms on the coating surface. Herein, we report an antifouling strategy to improve the fouling release performance of antifouling coatings by control the surface free energy and elastic modulus. Natural biomass cardanol-based benzoxazine monomers with different structures were designed by molecular structure and successfully synthesized via Mannich condensation. Detailed information of the chemical structure for the benzoxazines are analyzed by nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopies. In addition, the benzoxazines polymerization behavior is investigated by differential scanning calorimetry (DSC) analyses. The properties such as surface free energy and elastic modulus of polybenzoxazine were adjusted by the structure of the amine source. Notably, polybenzoxazines with octadecylamine as amine source have higher contact angle and lower surface free energy, and their elastic modulus is significantly lower than that of the octylamine benzoxazine. The elastic modulus of the octylamine benzoxazine was 732.5 MPa, while that of octadecylamine benzoxazine was only 24.0 MPa. Therefore, the polybenzoxazine coating has less fouling adhesion and exhibits better fouling release performance, and thus has better antifouling properties. This non-releasing polybenzoxazines without antifouling agent is a green, eco-friendly antifouling coating with low surface energy and low elastic modulus designed by molecular structure.

Amphiphilic Balance: Effect of the Hydrophilic-Hydrophobic Ratio on Fouling-Release Surfaces.

This study demonstrated the importance of identifying the optimal balance of hydrophilic and hydrophobic moieties in amphiphilic coatings to achieve fouling-release (FR) performance that surpasses that of traditional hydrophobic marine coatings. While there have been many reports on fouling-release properties of amphiphilic surfaces, the offered understanding is often limited. Hence, this work is focused on further understanding of the amphiphilic surfaces. Poly(ethylene glycol) (PEG) and polydimethylsiloxane (PDMS) were used to create a series of noncross-linked amphiphilic additives that were then added to a hydrophobic-designed siloxane-polyurethane (SiPU) FR system. After being characterized by ATR-FTIR, XPS, contact angle analysis, and AFM, the FR performance was evaluated by using different marine organisms. The assessments showed that the closer the hydrophilic and hydrophobic moieties in a system reached a relatively equalized level, the more desirable the FR performance of the coating system became. A balanced ratio of hydrophilicity-hydrophobicity in the system at around 10-15 wt % of each component had the best FR performance and was comparable to or better than commercial FR coatings.

Influence of multi-walled carbon nanotubes/N, N-dimethylformamide slurry amount on fouling release performance of silicone coatings

MWCNTs reinforced silicone coatings were prepared by mechanically mixing hydroxyl-capped polydimethylsiloxane (PDMS) and multi-walled carbon nanotubes/N, N-dimethylformamide (MWCNTs/DMF) slurries. The effects of MWCNTs/DMF slurry amount on the fouling release performance of silicone coatings were investigated. Incorporation of 5 wt% MWCNTs/DMF slurry increased the elongation and reduced Young's modulus, Shore's hardness, and roughness observed. As a result, an excellent silicone coating was fabricated with stable surface properties, fouling release performance, economic savings, and prolonged longevity for marine applications. Silicone coatings reinforced by MWCNTs were prepared by mechanical blending. MWCNTs are tubular crystals 30–80 nm in diameter and less than 10 μm long. The effects of MWCNTs/DMF slurry amount on the coating properties were investigated by dispersion properties, surface properties, mechanical properties, marine bacteria adhesion, and Navicula tenera adhesion test. The most favorable fouling release performance with the lowest roughness (0.168 ± 0.008 μm), the minimum Shore's hardness (18.47 HA), and the minimum relative adhesion factor (5.88 RAF) were shown for the silicone coatings prepared with 5 wt% MWCNTs/DMF slurry.

Magnetically controlled interface weaving of dual-layer heterogeneous coatings with active and passive anti-corrosion protection

Polydimethylsiloxane (PDMS) elastomer exhibiting remarkable corrosion resistance and fouling release properties. However, their performances are often compromised due to the weak interfacial adhesion with rigid substrates. Herein, we have developed an innovative dual-layer heterogeneous coating via magnetic-controlled interface weaving technology, achieving a seamless integration of PDMS with a rigid epoxy (EP) substrate. Magnetic nanoparticles (Fe3O4@MPDA-MBT) were strategically incorporated into the coating system, guided by a magnetic field to facilitate their interfacial migration. This controlled migration of nanoparticles resulted in the formation of interface layer between the EP primer and PDMS topcoat, leading to a sharp increase in PDMS adhesion strength (3.0 MPa), which is over 7 times greater than that of control counterpart (0.4 MPa). Additionally, Fe3O4@MPDA-MBT were selectively enriched adjacent to the metal substrate, thereby endowing the coating with outstanding corrosion resistance, due to the quick releasing of enough MBT inhibitors, as confirmed by electrochemical tests with high corrosion resistance value (2.2 × 108 Ω·cm2). Also, the topcoat PDMS enabled the dual-layer heterogeneous coating to achieve fouling-release and cavitation resistance.

Effects of incorporated silicone oils on the antifouling and drag reduction of Fe2O3/PDMS coatings

To develop an environmentally friendly fouling release coating, the effects of different silicone oils on the antifouling and drag reduction of the coating based polydimethylsiloxane (PDMS) reinforced iron oxide (Fe2O3) were investigated. The Fe2O3/PDMS coatings incorporated phenylmethyl silicone oil (PSO), methyl silicone oil (MSO), and a mixture of PSO and MSO were prepared. The surface morphology of the coating and the leaching rate of silicone oil were characterized by CLSM. The mechanical properties, anticorrosion, antifouling, and drag reduction performance of the coating were tested through the stress-strain curves, pull-out test, EIS, bacterial and diatom adhesion experiment, and single turntable torque experiment. Results revealed the leaching rate of PSO was the highest in the air. The hydrophobicity, the surface free energy, the multiple interlayer adhesion strength, the anticorrosion, the resistance to bacterial biofilms and Navicula tenera adhesion, and the drag reduction of the coating with PSO (IO-PSO) were better than those of the coating with MSO (IO-MSO). |Z|1 Hz for the coating IO-PSO immersed for 720 h can still reach the order of 1011 Ω cm2. The maximum drag reduction rate of the coating IO-PSO at 1600 rpm was 3.52 % compared to the epoxy coating.

A simple antifouling coating selection exhibits notable benefits for industrial fishing vessels

Impacts of biofouling were evaluated in-real conditions as a decision support system for industrial purse seiners and trawlers operating in the Mediterranean and the Black Sea (GFCM) in a fishing season. Initially, face-to-face interviews determined the most commonly used antifouling coatings among fishermen, resulting in the selection of five self-polishing copolymer (SPC) coatings. These SPC coatings, along with an uncoated reference panel, were immersed in the Black Sea's natural seawater environment for periodic fouling accumulation observations (SPC immersion tests). Additionally, selected SPC coating patches were applied on a fishing vessel to compare performances of the SPC coatings under the same conditions after a year of operation (namely ship tests). These ship test results were then compared with the outcomes from the static immersion tests. Finally, case studies were employed with the data generated from the static immersion tests for three fishing vessels operating in two different locations equipped with either trawl or purse seine. In addition to SPC coatings, foul release (FR) coatings were tested to compare their performance. Results indicated that applying an SPC coating to an industrial fishing vessel can yield fuel savings of 6%–10.26%, while a basic antifouling coating choice can save up to 3.11% in total fuel consumption over a fishing season in the GFCM area. Regardless of fishing gear used (purse seiner or trawler) or location of fishing activities conducted (Mediterranean or Black Sea), antifouling coating selection decision can reduce fuel consumption by up to 146.1M litres, fuel costs by £112.5M, and CO2 emissions by 0.42M tonnes for the regional GFCM fleet. These numbers are extrapolated to global fleet, estimating that fuel consumption can be decreased by up to 660.37M litres, fuel costs by £508.48M, and CO2 emissions by 1.9M tonnes based on the antifouling selection.

Behavior of biocide-free foul control paints for ships’ hulls in the immediate proximity of ICCP anodes

AbstractImpressed current cathodic protection systems are used in combination with organic coatings to prevent corrosion of hulls. The reaction species which are formed in the proximity of the anodes, like chlorinated compounds and acidity, can stress the antifouling paints of the protective coating system. A 3 × 3 matrix was defined to drive the tests aiming to investigate the behavior of novel biocide-free foul release (FR) and self-polishing (SP) paints under this kind of attack. The matrix was featured by different pH and free chlorine (free-Cl) values derived by a galvanostatic test performed at an anodic current density required for the protection of paints roughly at their mid age. Chemical/physical characterization was performed through visual analysis, thickness measurements, profilometry, contact angle measurements, and FTIR-ATR analysis. Both FR and SP paints underwent adhesive failure only in the harshest conditions, pH = 3/free-Cl 3–6 ppm, with unmodified chemistry of the polymers. Both paints exhibited no detachment in milder pH/free-Cl conditions, but thickness and contact angle reduction were observed. Finally, results were discussed inferring possible behaviors of the tested paints in real applications.

Silicone-modified polyurea-interpenetrating polymer network fouling release coatings with excellent wear resistance property tailored to regulations

The invasion of alien species via marine organisms attaching to the surfaces of ship hulls is a growing problem. A number of countries have introduced corresponding regulations to combat ship biofouling. One effective way to solve this problem is to apply a fouling release coating with excellent wear resistance. In this study, a silicone-modified polyaspartic ester polyurea was synthesized by a simultaneous crosslinking polymerization. Polyaspartic ester polyurea is employed to form a tightly cross-linked network with excellent toughness and outstanding adhesion, while polydimethylsiloxane is used to form a relatively soft cross-linked network with low surface energy and surface elasticity modulus. Polyurea and silicone molecular chain lock onto each other to form interpenetrating polymer network (IPN) through their respective polymerization systems and cross-linking processes. The synergy between silicone and polyurea provides excellent mechanical properties as well as fouling release performance through the locking mechanism. This study provides a promising and universal strategy for the development of fouling release coatings with excellent wear resistance.

Transparent amphiphilic silicone-based fouling-release coatings: Analyzing the effect on coating-fouling interfacial behavior

The amphiphilic antifouling coatings are effective for inhibiting fouling adhesion. Herein, the amphiphilic coatings were prepared by introducing polyether-modified polydimethylsiloxane (PE-PDMS). Uniform morphology, high transmittance, low surface roughness and amphiphilic property were obtained. PE-PDMS appearing as interspersed chains endowed the coating with amphiphilic characteristic. The artificial seawater promoted the migration of polyether to the surface. The protein adhesion force and quality were significantly reduced according to AFM-based colloidal probe technique and Quartz Crystal Microbalance with Dissipation, respectively. The coating exhibited antibacterial activity against Pseudoalteromonas xiamenensis (84.0%), Escherichia coli (69.2%) and Staphylococcus aureus (63.0%), respectively. 63.1% Halamphora. sp and 75.8% Nitzschia closterium f. had been inhibited, while the coatings possessed outstanding fouling release property with above 76.1% diatom detached after water exposure, proving that the amphiphilic parts weakened the adhesion of fouling. The mussel settlement assay confirmed that less adhesive plaques existed over the amphiphilic coatings. In addition, the expression for mussel adhesion proteins (mfp-5 and mfp-6) were significantly increased, demonstrating that amphiphilic polymers interfered with the adhesion response of the mussels. The effect on the interfacial behavior between fouling and coating is explored, providing a meaningful issue for the development of environmentally friendly antifouling coatings.

Anti-Fouling Properties of Phosphonium Ionic Liquid Coatings in the Marine Environment.

Biofouling is the buildup of marine organisms on a submerged material. This research tests the efficacy of phosphonium ion gels comprising phosphonium monomers ([P444VB][AOT] and [P888VB][AOT]) and free ionic liquid ([P4448][AOT], [P88814][AOT]) (10 to 50 wt%), varying copper(II) oxide biocide concentrations (0 to 2 wt%), and the docusate anion [AOT]- for added hydrophobicity. The efficacy of these formulations was tested using a seachest simulator protected from light and tidal currents in New Zealand coastal waters over the summer and autumn periods. Anti-fouling performance was correlated with the hydrophobicity of the surface (water contact angle: 14-131°) and biocide concentration. Formulations with higher hydrophobicity (i.e., less free ionic liquid and longer alkyl chain substituents) displayed superior anti-fouling performance. The presence of the copper(II) biocide negatively affected anti-fouling performance via significant increases to hydrophilicity. No correlation was observed between antimicrobial activity and anti-fouling performance. Overall, phosphonium ion gels show potential for combining anti-fouling and foul release properties.

Coatings to Reduce Fouling in Plate Heat Exchangers: Two Case Studies

Fouling of heat exchangers in the chemical industry, oil & gas industry, district heating, power plants, among others, results in a loss of performance which leads to production stops for cleaning and therefore increased operation costs. One approach to mitigate fouling is to alter the properties of the metal surface. A coating to be successful in any plate heat exchanger (PHE) application needs to have a good adhesion to the metal but also keep the heat transfer through the metal plates as unaltered as possible. This requires a thin coating with a relatively good thermal conductivity. The plates in a PHE are subjected to plate-to-plate contact point wear when in operation which also puts an extra requirement for the coating. To be suitable, the coating needs to have a good mechanical stability to resist this plate-to-plate wear. Alfa Laval has a long experience in coating plates for diverse applications and in this paper two case studies will be presented. One in the paper industry and the other in the biofuel industry. A new type of multilayer Teflon™ coating from Chemours was used, specifically designed to show excellent fouling release properties along with limited thicknesses (30–50 microns).

Capsaicin-based silicone antifouling coating with enhanced interlocking adhesion via SIPN

Silicone-based coatings generally exhibit excellent dynamic fouling release due to their low surface energy and elastic modulus. However, the poor adhesion of these coatings at the interface between the coating and the substrate, as well as deficient static antifouling capabilities, severely deteriorate their antifouling properties over extended periods. Herein, an epoxy-poly(dimethylsiloxane)/capsaicin (EP-PDMS/CAP) coating with highly enhanced interfacial adhesion and remarkable antifouling performances was prepared. The coating adhesion strength of the EP-PDMS/CAP has been improved by more than 5 times compared to a PDMS control coating (from 0.4 MPa to 2.04 MPa) by forming a semi-interpenetrating polymer network (SIPN) structure between the epoxy and PDMS layers. The EP-PDMS/CAP coating achieved the superior antifouling effects in both static and dynamic conditions, the anti-bacterial rate was as high as 96.8 %, and the anti-algal adhesion rate to the green algae Chlorella increased by 95.7 %, due to the synergistic effects of the fouling release performance from the PDMS coating and the fouling prevention of capsaicin. Furthermore, the EP-PDMS/CAP coating was proven to be extremely stable in different treatments such as acid/basic solutions, air oven heating test, and cyclic sand abrasion, showing great potential for anti-biofouling under aggressive conditions. This work provides a promising pathway towards the development of high-performance silicone-based composite coatings for efficient marine anti-biofouling.

Highly stable fluorine-free slippery liquid infused surfaces

A promising Slippery Liquid Infused Surface (SLIS) has been developed, that is both easy-to-produce and environmentally friendly. Using a double replication method, a 200 µm-thick texturized cross-linked PDMS film was obtained, leading to a grid of micrometric hills and deep wells. A comparison between perfluoropolyether (PFPE) lubricant and silicone oil of different viscosities highlights the advantage of silicone oil, which penetrates the cross-linked PDMS matrix even at high viscosity. Chemical modification with OTS (octadecyltrichlorosilane) and introduction of secondary structures through plasma etching, increased the surface's shear resistance. As a result, stable sliding properties were maintained after hundreds of cycles of immersion in water and, more originally still after tests under wind blowing exposure up to 78 m/s. Furthermore, addition of water sprayed during wind blowing exposure allows partial fouling release of the surface.