PDMS-based Coatings Research Articles

Marine biofouling mitigation of PDMS-based network coating with cross-linked contact- and release-active organoalkoxysilane

Poly (dimethylsiloxane) (PDMS) elastomer is one of key polymer resins for fouling release (FR) coatings, but it shows extremely poor antifouling (AF) activity in seawater since bacteria and diatoms could readily attach to surface. Modifying PDMS-based coatings via incorporating antifouling additives is effective for enhancing overall FR and AF activity. In this work, we prepared a well-defined organoalkoxysilane coating additive with quaternary ammonium and benzoisothiazolinone pendent groups, and the synthesized copolymers were covalently conjugated onto PDMS network in a one-pot reaction. AF and FR activities of the modified PDMS coatings were studied against soft fouling microorganisms. When microorganisms come into contact the coating surface, contact-active action mode works, quaternary ammonium groups could cause bacteria cell membrane disruption and microalgae photosynthesize inhibition via positive charge. Unexpectedly, a surprisingly lasting antimicrobial efficiency could be still observed in the neighboring coating, even the top-surface was completely covered with bacteria biofilm. Chemically conjugated benzoisothiazolinone could be sustainably released via side-group hydrolysis, thus, repelling and preventing the planktonic foulings from approaching the coating surface via release-active action mode. The modified PDMS coating with dual antifouling action modes could inhibit the biofilm formation at solid-liquid-air three-phase contact line, and could find valuable applications in marine transportation, water treatment and other antifouling fields.

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.

In-depth analysis of the effect of physicochemical properties of ionic liquids on anti-icing behavior of silicon based-coatings

This study dissects the use of room temperature ionic liquids (RT-ILs) in a dynamic surface for anti-icing applications. Anti-icing properties of ILs-containing PDMS-based coatings fabricated by two different types of ILs, are evaluated to establish a relationship between the anti-icing behavior and physicochemical properties of the ILs. The surface chemistry of coatings and the existence of distinctive groups of the ILs anions on the surface of coatings characterized by Attenuated Total Reflectance-Fourier transform infrared (FTIR) spectroscopy (ATR-FTIR) and confirmed by using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy-energy dispersive X-ray analysis (SEM/EDX). The 3D profiles and roughness parameter of the surfaces were investigated by a confocal laser microscopy profiler. Regarding the importance of correlation between wettability and ice adhesion, the wettability of coatings was studied. The results show a significant reduction 30–40% in sliding angle (SA) and contact angle hysteresis (CAH) in ILs-containing coatings. Differential scanning calorimetry (DSC), freezing delay time, push-off and centrifugal adhesion tests (CAT) served to distinguish the performance of the two ILs in regard to ice nucleation temperature and formation time, and ice adhesion strength, respectively. The 60–70% reduction in ice adhesion strength for the IL-containing coatings, obtained by push-off test, is due to the presence of strong ionic hydrogen bounded water and the formation of self-lubricating quasi liquid layer that can function at much lower temperature. Solid-state nuclear magnetic resonance (NMR) spectroscopy has confirmed the presence of nonfrozen water molecules at the interface. Consequently, incorporating ILs into coatings provides an effective approach to delay ice nucleation, restrict ice growth recrystallization and reduce ice adhesion strength. A comparison of enhanced anti-icing performance of ILs-containing coatings highlights the significant influence of minor changes in the chemical structure of ILs on their potential for anti-icing applications.

Insights into the antimicrobial properties of a cationic steroid and antibiofilm performance in PDMS-based coatings to potentially treat urinary infections.

Currently, multidrug-resistant (MDR) infections are one of the most important threats, driving the search for new antimicrobial compounds. Cationic peptide antibiotics (CPAs) and ceragenins (CSAs) contain in their structures cationic groups and adopt a facially amphiphilic conformation, conferring the ability to permeate the membranes of bacteria and fungi. Keeping these features in mind, an amine steroid, DOCA-NH2, was found to be active against reference strains and MDR isolates of Gram-positive Enterococcus faecalis and Staphylococcus aureus and Gram-negative Escherichia coli and Pseudomonas aeruginosa. The compound was active against all the tested microorganisms, having bactericidal and fungicidal activity, displaying minimal inhibitory concentrations (MICs) between 16 and 128 μg mL-1. No synergy with clinically relevant antibacterial drugs was found. However, the compound was able to completely inhibit the biofilm formation of bacteria exposed to the MIC of the compound. For E. coli and E. faecalis, inhibition of biofilm formation occurred at half the MIC. Besides, DOCA-NH2 inhibited the dimorphic transition of Candida albicans at concentrations 4 times lower than the MIC, and can reduce the microorganism virulence and biofilm formation was significantly reduced at both MIC and half the MIC. Polydimethylsiloxane-based coatings containing DOCA-NH2 (0.5, 1.0, and 1.5 wt%) were prepared and tested against the E. coli biofilm formation under hydrodynamic conditions similar to those prevailing in ureteral stents. A biofilm reduction of approximately 80% was achieved when compared to the control.

Corrosion protection on texturized steel moulds for polymeric products by sol–gel anti-adherent coatings

During the moulding of polymeric pieces, the important temperatures involved, and the gases produced by decomposition of components from the polymer can induce corrosion on the working surface of the steel mould. Polymers can also stick to the mould surface, being their separation (demoulding) one of the critical aspects in their processing. Demoulding agents typically used in this process are expected to contribute in some extend to protect the mould against corrosion. In this work, hybrid sol–gel technology for anti-adherent coatings presented in previous papers is extended to formulations doped with different metallic precursors of proven chemical and wear resistance such as Zn, Ti, and Zr, with the aim to increase the corrosion resistant at the same time that keep good demoulding properties. Different synthetic routes one-pot or two components were followed depending on the doped agent. Sol–gel formulations were applied onto steel substrates by controlled dip coating technique, resulted in ultra-thin films of ∼0.15 µm, being capable to protect micro texturized steel moulds. Hardness of these films was superior (10H) to those formulations with fluorosilane and PDMS used as reference. Corrosion protection was evaluated obtaining good results in both polarization resistance and corrosion rate for Zn (5232 Ω × cm2, 0.08 mm/year), protecting the bare steel up to 6.5 times more in terms of annual corrosion, followed by Zr and Ti. Their behaviour as anti-adherent coating was also discussed and compared with fluorosilane and PDMS-based coatings.

A Close-Up of Anti-Icing Performance of Pdms-Based Coatings Containing Ionic Liquids

A Close-Up of Anti-Icing Performance of Pdms-Based Coatings Containing Ionic Liquids

A substrate-independent isocyanate-modified polydimethylsiloxane coating harvesting mechanical durability, self-healing ability and low surface energy with anti-corrosion/biofouling potential

Polydimethylsiloxane (PDMS)-derived materials have been used as functional coatings in a wide range of industrial and engineering applications owing to their appealing physical and chemical properties. However, most of them cannot harvest mechanical durability, self-healing ability and low surface energy due to the conventional chemical crosslinking method. Herein, a polymer coating featuring multifaceted functionalities is developed by facilely brush-coating isocyanate-modified PDMS (I-PDMS) on diverse substrates, in which the adjacent polymer chains are physically crosslinked by the hydrogen bonds between the urea motifs. The prepared coating can withstand 500 cycles of adhesive tape-peeling or 200 cycles of sandpaper abrasion without losing its hydrophobicity. Besides, the dynamic nature of the intermolecular hydrogen bonds leads to appreciable self-healing ability which can essentially extend the coating’s lifespan. Moreover, the I-PDMS coating possesses low surface energy, i.e., ∼ 13.1 mJ/m2 and ∼ 28.8 mJ/m2 when the PDMS Mw is ∼ 30000 and ∼ 3000, respectively. These appealing properties strongly depend on the PDMS Mw which could be attributed to the variation in mobility of the polymer chains and density of the intermolecular hydrogen bonds. Furthermore, it is found that this I-PDMS coating can effectively mitigate corrosion and biofouling on metal substrates, implying its great potential as a protective coating in practical engineering processes. Our work offers a promising approach to prepare multifunctional PDMS-based coatings with considerable application prospect.

Amphiphilic Polyphosphonate Copolymers as New Additives for PDMS-Based Antifouling Coatings.

Poly(ethyl ethylene phosphonate)-based methacrylic copolymers containing polysiloxane methacrylate (SiMA) co-units are proposed as surface-active additives as alternative solutions to the more investigated polyzwitterionic and polyethylene glycol counterparts for the fabrication of novel PDMS-based coatings for marine antifouling applications. In particular, the same hydrophobic SiMA macromonomer was copolymerized with a methacrylate carrying a poly(ethyl ethylene phosphonate) (PEtEPMA), a phosphorylcholine (MPC), and a poly(ethylene glycol) (PEGMA) side chain to obtain non-water soluble copolymers with similar mole content of the different hydrophilic units. The hydrolysis of poly(ethyl ethylene phosphonate)-based polymers was also studied in conditions similar to those of the marine environment to investigate their potential as erodible films. Copolymers of the three classes were blended into a condensation cure PDMS matrix in two different loadings (10 and 20 wt%) to prepare the top-coat of three-layer films to be subjected to wettability analysis and bioassays with marine model organisms. Water contact angle measurements showed that all of the films underwent surface reconstruction upon prolonged immersion in water, becoming much more hydrophilic. Interestingly, the extent of surface modification appeared to be affected by the type of hydrophilic units, showing a tendency to increase according to the order PEGMA < MPC < PEtEPMA. Biological tests showed that Ficopomatus enigmaticus release was maximized on the most hydrophilic film containing 10 wt% of the PEtEP-based copolymer. Moreover, coatings with a 10 wt% loading of the copolymer performed better than those containing 20 wt% for the removal of both Ficopomatus and Navicula, independent from the copolymer nature.

Eco-friendly foul release coatings based on a novel reduced graphene oxide/Ag nanocomposite prepared by a green synthesis approach

The purpose of making graphene/polydimethylsiloxane (PDMS)-based coatings is providing a suitable strategy to prevent fouling organism adhesion. In this study, graphene oxide (GO) reduced with Avicennia marina/Silver to achieve GOH@Ag nanocomposite. GOH@Ag, bare GO and multi-Wall Carbon nanotubes (MWCNTs) as nanofillers were individually incorporated into PDMS-based coatings with 0.01, 0.1, and 0.5 %wt. The surface characterization including pseudo-barnacle adhesion strength and water static contact angle and critical surface energy was performed for all samples. Evaluating field immersion was performed due to the samples in the natural seawater. The best results were observed for the sample with 0.5 wt% of GOH@Ag (RMS roughness = 103 nm, pseudo-barnacle adhesion strength =0.16 MPa, critical surface energy = 16 mN/m, static contact angle = 118.8°). The simultaneous presence of A. marina and silver element in the structure of graphene-based nanocomposite showed a synergistic effect on the performance of PDMS-based coatings which achieved outstanding result of antifouling efficiency (N = 18).

Design and preparation of icephobic PDMS-based coatings by introducing an aqueous lubricating layer and macro-crack initiators at the ice-substrate interface

Preventing ice accretion on exposed surfaces is important to the operational performance of various facilities and devices. As time elapses and temperature lowers sufficiently, ice accretion becomes inevitable. Herein, we present a new approach to prepare icephobic coatings by incorporating two strategies towards lowering ice adhesion strength, i.e. introducing an aqueous lubricating layer and maximizing macro-crack initiators at the ice-substrate interface. The aqueous lubricating layer is realized by grafting poly(acrylic acid) (PAA) onto polydimethylsiloxane (PDMS) coatings, and the macro-crack initiators are induced by introducing macro-scale hollow sub-surface structures into PDMS coatings. By using vertical shear tests, ice adhesion strengths of PAA-g-PDMS (10:1), PDMS coatings with macro-scale hollow sub-surface structures (hPDMS) (10:1), PAA-g-hPDMS (10:1), PAA-g-PDMS (10:10), hPDMS (10:10), and PAA-g-hPDMS (10:10) coatings are obtained as 178.5 ± 22 kPa, 153.1 ± 19 kPa, 122.7 ± 18 kPa, 24.6 ± 4 kPa, 20.3 ± 3.4 kPa and 17.6 ± 3.2 kPa, respectively, showing a reduction of 37.2 %, 46.1 %, 56.8 %, 32.8 %, 44.5 % and 51.9 % when compared with corresponding pure PDMS coatings. These results indicate that ice adhesion strength can be further reduced by simultaneously introducing two strategies. The principle of designing icephobic coatings by combining two or more strategies to reduce ice adhesion to as low as possible provides a new avenue to the preparation of icephobic coatings, and makes practical applications possible under extremely severe conditions.

High-throughput sequencing analysis of marine pioneer surface-biofilm bacteria communities on different PDMS-based coatings

Marine biofilms, the attachment of marine microorganisms on artificial surfaces in natural seawater, play critical roles in the development of marine biofouling, which pave ways for the settlement and colonization of sessile invertebrate larvae. Despite the excellent microbe-inhibitory effect of polydimethylsiloxane (PDMS)-based coatings, marine bacteria could still attach to surfaces and form natural biofilms. However, there is little information available on the common structural features of pioneer surface-biofilm bacteria (PSB) communities on different PDMS-based coatings with regard to their compositions, distributions and diversity. Herein, the present study aims to explore the compositional and structural features of the PSB communities on different PDMS-based coatings using 16S rRNA gene amplicon sequencing in terms of the taxonomic structures at phylum, family and genus level. The results revealed the PSB communities on different PDMS-based coatings possessed high similarities in compositional, structural and diversity features, but varied greatly in relative abundance and distributions. Proteobacteria was the most diverse and overwhelming phylum in biofilms formed on all PDMS-based coatings, followed by Cyanobacteria. In addition, the decreased abundance of Proteobacteria and the increased abundance of Cyanobacteria on the carbon nanotubes (CNTs)-modifed PDMS composites (CPCs) may contribute to their differential anti-biofouling effect against the colonization of juvenile macrofoulers.

Visualization of the distribution of surface-active block copolymers in PDMS-based coatings

Poly(dimethylsiloxane) (PDMS) has been widely employed in the area of fouling-release coatings and other fields due to its unique combination of properties including low elastic modulus and low glass transition temperature. The drawback of PDMS in some applications is its hydrophobic surface, which results in non-specific protein adsorption and wettability issues. Poly(ethylene glycol)-based surface-active block copolymers and surfactants have been added to PDMS coatings and films to impart biofouling resistance and hydrophilicity to the PDMS surface with successful results. Information regarding the distribution and release of these block copolymers from PDMS-based coatings has been previously reported. However, the distribution and behaviour of these compounds in the bulk of the PDMS coating are not fully understood.A novel fluorescent-labelled triblock PEG-b-PDMS-b-PEG copolymer was synthesized and added to a PDMS coating for visualization purposes. The surface-activity and biofouling resistance of the synthesized copolymer was confirmed by water contact angle measurements and seawater immersion experiments. Confocal laser scanning microscopy (CLSM) images showed that the triblock copolymer aggregates in spherical domains within the PDMS coating film. The size of these domains vary between 1 and 7 μm, with larger domains being present on the bulk of the film and smaller closer to the surface. The diffusion of the copolymer could be observed over time, with copolymer molecules diffusing from the bulk to the surfaces of the PDMS film. Finally, an overview of the possibilities provided by the presented methodology in the field of fouling-release coatings is discussed.

Diffusion of surface-active amphiphiles in silicone-based fouling-release coatings

Abstract Amphiphiles (i.e. amphiphilic molecules such as surfactants, block copolymers and similar compounds) are used in small amounts to modify the surface properties of polymeric materials. In silicone fouling-release coatings, PEG-based amphiphiles are added to provide biofouling-resistance. The success of this approach relies on the ability of the amphiphiles to diffuse through the coating film and cover the surface of the coating. A novel method for the measurement of diffusion coefficients of PEG-based amphiphiles of different chemistries in PDMS-based coatings is presented here. The diffusion coefficient of the amphiphiles shows a weak dependency on their molecular weight, although this dependency is much less pronounced than for other rubbery polymeric materials. The biofouling-resistance properties in fouling-release coatings were also studied for these amphiphiles. It was found that the diffusion coefficient does not have any influence on the biofouling-resistance results for the studied compounds. Instead, the chemistry of the hydrophobic block of the amphiphiles is much more significant, with PEG-PDMS block copolymers showing the best properties among the studied compounds.

Efficient Flame Retardant Thin Films Synthesized by Atmospheric Pressure PECVD through the High Co-deposition Rate of Hexamethyldisiloxane and Triethylphosphate on Polycarbonate and Polyamide-6 Substrates.

An innovative approach to produce high-performance and halogen-free flame-retardant thin films at atmospheric pressure is reported. PDMS-based coatings with embedded dopant-rich polyphosphates are elaborated thanks to a straightforward approach, using an atmospheric pressure dielectric barrier discharge (AP-DBD). Deposition conditions have been tailored to elaborate various thin films that can match the fire performance requirements. Morphology, chemical composition, and structure are investigated, and results show that the coatings performances are increased by taking advantage of the synergistic effect of P and Si flame retardant compounds. More specifically, this study relates the possibility to obtain flame retardant properties on PolyCarbonate and PolyAmide-6 thanks to their covering by a 5 μm thick coating, i.e. very thin films for this field of application, yet quite substantial for plasma processes. Hence, this approach enables deposition of flame retardant coatings onto different polymer substrates, providing a versatile fireproofing solution for different natures of polymer substrates. The presence of an expanded charred layer at the surface acts as a protective barrier limiting heat and mass transfer. This latter retains and consumes a part of the PC or PA-6 degradation byproducts and then minimizes the released flammable gases. It may also insulate the substrate from the flame and limit mass transfers of remaining volatile gases. Moreover, reactions in the condensed phase have also been highlighted despite the relatively thin thickness of the deposited layers. As a result of these phenomena, excellent performances are obtained, illustrated by a decrease of the peak of the heat release rate (pHRR) and an increase of the time to ignition (TTI).

A comparison between different fouling-release elastomer coatings containing surface-active polymers

Surface-active polymers derived from styrene monomers containing siloxane (S), fluoroalkyl (F) and/or ethoxylated (E) side chains were blended with an elastomer matrix, either poly(dimethyl siloxane) (PDMS) or poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS), and spray-coated on top of PDMS or SEBS preformed films. By contact angle and X-ray photoelectron spectroscopy measurements, it was found that the surface-active polymer preferentially populated the outermost layers of the coating, despite its low content in the blend. However, the self-segregation process and the response to the external environment strongly depended on both the chemistry of the polymer and the type of matrix used for the blend. Additionally, mechanical testing showed that the elastic modulus of SEBS-based coatings was one order of magnitude higher than that of the corresponding PDMS-based coatings. The coatings were subjected to laboratory bioassays with the marine alga Ulva linza. PDMS-based coatings had superior fouling-release properties compared to the SEBS-based coatings.