Research Progress on Low-Surface-Energy Antifouling Coatings for Ship Hulls: A Review.

A desired approach to reduce bacterial adhesion to ship hull, heat exchanger and medical device surfaces is to make them less attractive for bacteria by applying anti-fouling or foul-release surface coatings. However, the selection of a useful anti-fouling coating is a difficult problem and surface thermodynamics may guide us in this respect. In this work, we investigated the independent contributions of substrate–water, γ SW Tot, substrate–bacteria, γ SB Tot, and bacteria–water, γ BW Tot, interfacial free energies to the total free energy of adhesion, ΔG SWB Tot, of Pseudomonas fluorescens bacteria on the Si- and SiN-doped DLC coated glass slide surfaces using the Lifshitz–van der Waals and acid–base surface free energy components theory. It was found that mostly acid–base interactions determine the bacterial removal properties. The repulsion between bacteria and the solid surface in water increases if γ SB AB is large and γ SW AB is small, when they are both positive. When Lifshitz–van der Waals and acid–base components of free energy of adhesion are considered, it was found that the effect of ΔG SWB LW was very small and the main effect on bacterial removal was found to depend on the ΔG SWB AB parameter and bacterial % removal increased linearly with the increase of both ΔG SWB AB and ΔG SWB Tot parameters for all the samples.

Antifouling (fouling control) coatings are used to protect underwater marine structures from the colonisation by organisms which can increase a structure's mass and reduce the efficiency of vessels. Antifouling coatings, which are used to present their attachment, contain biocidal pigments, such as cuprite (CU20) readily realising CU2+ ions into the environment, which are toxic to fouling organisms at concentrations of 10 µg. cm−2. day−1. However, these coatings may form a blue-green patina surface
\nlayer, leading to unnecessary maintenance operations due to the perceived reduction
\nin protection and aesthetics, costing both time and money. Therefore, accelerated
\ntesting methodologies are required to reproduce naturally formed patina, allowing the
\npatination characteristics of different coating formulations to be observed, with the
\naim of reducing patina formation.
\n
\nWhile patination of copper in the marine environment has been extensively researched, there is less information on the patination of antifouling coatings. The analysis of patinated paint flakes removed from in-service vessels found that clinoatacamite Cu2Cl(OH)3 was the most commonly detected copper patina.
\n
\nDC electrochemical tests were then carried out to determine the most appropriate
\nenvironments that would result in an acceleration in antifouling coating patination.
\nClinoatacamite developed in chloride containing electrolytes, with the 10% sodium
\nchloride electrolyte having the highest corrosion rate, while a further increase in
\ncorrosion rate was observed in elevated temperatures up to 55°C. Analysis of the
\nPourbaix diagrams for the different sodium chloride concentrations and temperatures
\nalso found that the stability domain for Cu2Cl(OH)3 occurred between pH 6 and 8.5
\nwith a neutral pH being selected for testing of the coatings. 
\n
\nThe blue-green clinoatacamite patina found on in-service vessels was reproduced
\nwhen testing under immersion, evaporation, and salt spray laboratory conditions. The
\nquickest patination rate and highest levels of clinoatacamite were observed in the
\nneutral 10% sodium chloride electrolyte under immersion conditions. This was
\nassociated with the increase in clinoatacamite density due to the reduction in patina
\nparticle size and an overall increase in the thickness of an adherent patina layer. This
\ntesting procedure allows for the rapid qualification of different antifouling coating
\nformulas and their resistance to patina formation, and therefore reduce the need for
\nthe reapplication of coatings prior to their expected end of service life.

Coordination-driven antifouling spray coating using a sulfated polysaccharide Fucoidan

ABSTRACTShip surface fouling poses serious constraints on ship navigation and the marine environment. Now that the traditionally harmful antifouling coatings have been banned worldwide, the development of new antifouling coatings for ships that are environmentally friendly and functionally stable is imminent. Low surface energy antifouling coatings with structural biomimetic properties are the safest, most environmentally friendly, and effective breakthrough in preventing fouling deposits on hull surfaces. This article first explains the antifouling mechanism of antifouling coatings, comprehensively describes the morphology of the bionic microstructure, and summarizes the construction method of the bionic structure. On this basis, the low surface energy properties of fluorine‐containing and silicone‐containing materials, as well as the current application development in antifouling coatings for ships, are analyzed. In addition, the article describes the application of stimulus–response in antifouling coatings. This article reviews the research progress in low surface energy coatings based on biomimetic structures in recent years, presents the current challenges and future development directions in this field, and provides unique insights to further optimize the performance of these antifouling coatings.

In the early stages after larval settlement, coral spat can be rapidly overgrown and outcompeted by algae, reducing overall survival for coral reef replenishment and supply for restoration programs. Here we investigated three antifouling (AF) coatings for their ability to inhibit algal fouling on coral settlement plugs, a commonly-used restoration substrate. Plugs were either fully or partially coated with the AF coatings and incubated in mesocosm systems with partial recirculation for 37 days to track fouling succession. In addition, settlement of Acropora tenuis larvae was measured to determine whether AF coatings were a settlement deterrent. Uncoated control plugs became heavily fouled, yielding only 4–8% bare substrate on upper surfaces after 37 days. During this period, an encapsulated dichlorooctylisothiazolinone (DCOIT)-coating was most effective in reducing fouling, yielding 61–63% bare substrate. Antiadhesive and cerium dioxide (CeO2−x) nanoparticle (NP) coatings were less effective, yielding 11–17% and 2% bare substrate, respectively. Average settlement of A. tenuis larvae on the three types of AF-coated plugs did not statistically differ from settlement on uncoated controls. However, settlement on the NP-coating was generally the highest and was significantly higher than settlement found on the antiadhesive- and DCOIT-coating. Furthermore, on plugs only partially-covered with AF coatings, larval settlement on coated NP- areas was significantly higher than settlement on coated antiadhesive- and DCOIT-areas. These results demonstrate that AF coatings can reduce fouling intensity on biologically-relevant timescales while preserving robust levels of coral settlement. This represents an important step towards reducing fine-scale competition with benthic fouling organisms in coral breeding and propagation.

As marine equipment advances from shallow to deep-sea environments, the demand for high-performance antifouling materials continues to increase. The lionfish, a species inhabiting both deep-sea and shallow coral reefs, prevents fouling organism adhesion via its smooth, mucus-covered skin, which contains antimicrobial peptides. Inspired by lionfish skin, this work integrates zwitterionic segments with hydration-based fouling-release properties and the furan oxime ester structure with intrinsic antibacterial activity to develop asilicone-based antifouling coating capable of operating from shallow to deep-sea environments. The coating exhibits excellent antifouling properties in shallow-water environments, completely inhibiting protein adhesion and reducing bacterial, algae adhesion by up to 33.23% and 85.23%, respectively. displays superior intrinsic bactericidal activity, achieving a 100% bactericidal rate. Field panel immersion tests confirmed the coating's effectiveness in preventing the adhesion of large shallow-water fouling organisms. After 51 days of immersion at a maximum depth of 7730 meters in the Mariana Trench, no live bacteria are detected on the coating surface, which remained in excellent condition and retained its full bactericidal efficacy. This antifouling coating presents a promising solution for marine equipment across full ocean depths adn expands applications in the marine industry.

Rare earth oxide nanoparticles for superhydrophobic, antifouling and self-cleaning coatings

Following the tributyl-tin antifouling coatings’ prohibition in 2003, global interest was directed toward non-toxic coatings as an eco-friendly alternative. Natural surfaces with superhydrophobicity exhibited exciting antifouling mechanisms. Efficient and eco-friendly antifouling coatings have been developed using bioinspired polymeric nanostructured composites. These superhydrophobic surfaces have rough topologies and low surface-free energies. Various organic/inorganic polymeric nanocomposites were developed for increasing fouling prevention by physical microfouling repulsion and chemical surface inertness. The biofouling costs and the difficulties of artificial antifouling coatings were also discussed in this chapter. It will introduce a cutting-edge research platform for next-generation antifouling surfaces for maritime navigation. This chapter aims to explain the evolution of superhydrophobic antifouling surfaces inspired by biological systems.

The extended immersion of ships in seawater frequently results in biofouling, a condition characterized by the accumulation of marine organisms such as barnacles and algae. To combat this issue, the application of anti-fouling coatings to the hull surfaces of vessels has emerged as one of the most effective strategies. In response to the increasing global emphasis on environmental sustainability, there is a growing demand for anti-fouling coatings that not only demonstrate superior anti-fouling efficacy but also adhere to stringent environmental standards. The traditional use of organotin-based self-polishing anti-fouling coatings, known for their high toxicity, has been prohibited due to environmental concerns. Consequently, there is a progressive shift toward the development and application of environmentally friendly anti-fouling coatings. This paper reviews the toxicity and application limitations associated with conventional anti-fouling coatings. It provides a comprehensive overview of recent advancements in the field, including the development of novel self-polishing anti-fouling coatings, low surface energy coatings, biomimetic coatings, and nanostructured coatings, each leveraging distinct anti-fouling mechanisms. The paper evaluates the composition and performance of these emerging coatings and identifies key technical challenges that remain unresolved. It also proposes a multi-faceted approach to addressing these challenges, suggesting potential solutions for enhancing the effectiveness and environmental compatibility of anti-fouling technologies. The paper forecasts future research directions and development trajectories for marine anti-fouling coatings, emphasizing the need for continued innovation to achieve both environmental sustainability and superior anti-fouling performance.

Any equipment submerged in the ocean will have its surface attacked by fouling organisms, which can cause serious damage. Traditional antifouling coatings contain heavy metal ions, which also have a detrimental effect on the marine ecological environment and cannot fulfill the needs of practical applications. As the awareness of environmental protection is increasing, new environmentally friendly and broad-spectrum antifouling coatings have become the current research hotspot in the field of marine antifouling. This review briefly outlines the formation process of biofouling and the fouling mechanism. Then, it describes the research progress of new environmentally friendly antifouling coatings in recent years, including fouling release antifouling coatings, photocatalytic antifouling coatings and natural antifouling agents derived from biomimetic strategies, micro/nanostructured antifouling materials and hydrogel antifouling coatings. Highlights include the mechanism of action of antimicrobial peptides and the means of preparation of modified surfaces. This category of antifouling materials has broad-spectrum antimicrobial activity and environmental friendliness and is expected to be a new type of marine antifouling coating with desirable antifouling functions. Finally, the future research directions of antifouling coatings are prospected, which are intended to provide a reference for the development of efficient, broad-spectrum and green marine antifouling coatings.

Motivated by extensive discussion in the literature, by experimental evidence and by recent direct numerical simulations, we study flows over hydrophobic surfaces with shear-dependent slip lengths and we report their drag-reduction properties. The laminar channel-flow and pipe-flow solutions are derived and the effects of hydrophobicity are quantified by the decrease of the streamwise pressure gradient for constant mass flow rate and by the increase of the mass flow rate for constant streamwise pressure gradient. The nonlinear Lyapunov stability analysis, first applied to a two-dimensional channel flow by Balogh et al. [“Stability enhancement by boundary control in 2-D channel flow,” IEEE Trans. Autom. Control 46, 1696-1711 (2001)], is employed on the three-dimensional channel flow with walls featuring shear-dependent slip lengths. The feedback law extracted through the stability analysis is recognized for the first time to coincide with the slip-length model used to represent the hydrophobic surfaces, thereby providing a precise physical interpretation for the feedback law advanced by Balogh et al. The theoretical framework by Fukagata et al. [“A theoretical prediction of friction drag reduction in turbulent flow by superhydrophobic surfaces,” Phys. Fluids 18, 051703 (2006)] is employed to model the drag-reduction effect engendered by the shear-dependent slip-length surfaces and the theoretical drag-reduction values are in very good agreement with our direct numerical simulation data. The turbulent drag reduction is measured as a function of the hydrophobic-surface parameters and is found to be a function of the time- and space-averaged slip length, irrespective of the local and instantaneous slip behaviour at the wall. For slip parameters and flow conditions that could be realized in the laboratory, the maximum computed turbulent drag reduction is 50% and the drag reduction effect degrades when slip along the spanwise direction is considered. The power spent by the turbulent flow on the hydrophobic walls is computed for the first time and is found to be a non-negligible portion of the power saved through drag reduction, thereby recognizing the hydrophobic surfaces as a passive-absorbing drag-reduction method. The turbulent flow is further investigated through flow visualizations and statistics of the relevant quantities, such as vorticity and strain rates. When rescaled in drag-reduction viscous units, the streamwise vortices over the hydrophobic surface are strongly altered, while the low-speed streaks maintain their characteristic spanwise spacing. We finally show that the reduction of vortex stretching and enstrophy production is primarily caused by the eigenvectors of the strain rate tensor orienting perpendicularly to the vorticity vector.

Technologies for reducing hydrodynamic skin-friction drag have a huge potential for energy-savings in applications ranging from propulsion of marine vessels to transporting liquids through pipes. The majority of previous experimental studies using hydrophobic surfaces have successfully shown skin-friction drag reduction in the laminar and transitional flow regimes (typically Reynolds numbers less than ≃106 for external flows). However, this hydrophobicity induced drag reduction is known to diminish with increasing Reynolds numbers in experiments involving wall bounded turbulent flows. Using random-textured hydrophobic surfaces (fabricated using large-length scalable thermal spray processes) on a flat plate geometry, we present water-tunnel test data with Reynolds numbers ranging from 106 to 9 × 106 that show sustained skin-friction drag reduction of 20%–30% in such turbulent flow regimes. Furthermore, we provide evidence that apart from the formation of a Cassie state and hydrophobicity, we also need a low surface roughness and an enhanced ability of the textured surface to retain trapped air, for sustained drag reduction in turbulent flow regimes. Specifically, for the hydrophobic test surfaces of the present and previous studies, we show that drag reduction seen at lower Reynolds numbers diminishes with increasing Reynolds number when the surface roughness of the underlying texture becomes comparable to the viscous sublayer thickness. Conversely, test data show that textures with surface roughness significantly smaller than the viscous sublayer thickness and textures with high porosity show sustained drag reduction in the turbulent flow regime. The present experiments represent a significant technological advancement and one of the very few demonstrations of skin-friction reduction in the turbulent regime using random-textured hydrophobic surfaces in an external flow configuration. The scalability of the fabrication method, the passive nature of this surface technology, and the obtained results in the turbulent regime make such hydrophobic surfaces a potentially attractive option for hydrodynamic skin-friction drag reduction.

Marine anti-fouling coatings have been widely used as one of the effective methods to prevent marine fouling organisms from adhering to the surfaces of various marine facilities. The main types are self-polishing anti-fouling coatings and low surface energy anti-fouling coatings, and biomimetic antifouling paint. Due to the increasing awareness of environmental protection, the anti-fouling coatings harmful to the environment have been gradually banned, so the research and development of new anti-fouling coatings has become the primary direction of development.In this paper, polycaprolactone and PLA were used as resin base materials, capsaicin as bio-friendly anti-fouling agent, starch as polysaccharide additive, the experimental samples were prepared by adjusting the mixture ratio of these materials. The experiment of adding starch and unadded starch was carried out by using Magnetic stirrer and other experimental equipment to simulate the hanging board method on the sea and observed and recorded, the effect of Starch on the hydrolysis of anti-fouling coatings using single component or blends of biodegradable materials such as polycaprolactone, polylactic acid (PLA) as resin matrix was investigated.The results showed that starch could promote the hydrolysis of resin-based materials such as PCL, and the solubility of PCL and PLA in chloroform was obtained, a preparation method of antifouling coating for marine static culture equipment was obtained.

Biofouling is the unwanted attachment of microorganisms on surfaces that are exposed or submerged under water. Biofouling has caused many serious problems especially the marine industry. The operational performance of marine vehicles such as ships will be negatively affected because of the build-up of biofouling organisms on the ships surface causing hydrodynamic drag. Several antifouling methods such as using toxic chemical coatings and manually removing the fouling organisms have been implemented but were unsustainable and costly. This leads to the investigation of natural and biomimetic surfaces that can solve complex engineering challenges such as drag reducing and antifouling surfaces that can save money and time. CFD analysis has shown that microorganisms on patterned surfaces will experience complex micro-hydrodynamic environment such as inconsistent velocity distribution, different strain rates, recirculation and distribution pattern of wall shear. Moreover, high shear bounded zones and steep fluctuating stress strain rate are microfluidic conditions that can inhibit the attachment of biofouling organisms. Many living sea creatures exhibit drag reducing and antifouling capabilities such as the shark skin riblet surface. The wall shear stress, fluid flow velocity and the development of vortices are useful in predicting the location of biofouling occurrence. Simulations on the shark skin surfaces shows the average velocity around the topography is 7.213 x 10-3 ms-1 and vortices were present between the gaps. The peak of each topography developed high wall shear stress but the bed of the topography experienced low wall shear stress which could lead to the potential build-up of biofouling. The investigation of the antifouling shell surface includes six different shell surface geometries that are simplified as V-shape riblet, U-shape riblet, space V-shape riblet, blunt V-shape riblet, L-shape riblet and ∩-shaped riblet. The velocity and shear stress analysis above the different shaped riblet surfaces were included. Moreover, the influence on the flow by different riblet shapes were also discussed. The knowledge gained from the discussion can aid to determine the optimal design of topography that can be applied to the ship’s hull. ANSYS fluent will be used to create the design for the ship’s surface. The ideal combination of size and geometry of topography based on literature will be selected. The 3D model of a few micro-sized topography surface will be produced. Tetrahedron method for meshing will be used for high accuracy. The analysis of hydrodynamic variations like wall shear stress, shear strain rates and flow velocity around the selected topographies will be determined. CFD simulations will be used to verify the antifouling performance of the topographies. The optimally designed micro-sized topographies that are simulated are expected to reduce the biofouling occurrence on a ship’s hull and reduce frictional drag during the sailing of ships.

Special issue on advanced corrosion-resistance materials and emerging applications. The progress on antifouling organic coating: From biocide to biomimetic surface