Silicone Coatings Research Articles

Role of dynamic surface tension of silicone polyether surfactant-based silicone coatings on protein adsorption: An insight on the ‘ambiguous’ interfacial properties of Fouling Release Coatings

Non-toxic antibiofouling coatings are currently developed to avoid the negative impacts of the settlement of (micro)organisms on any water immersed surfaces. In some industries such as microalgae culture, marine sensors or even contact lenses, in addition to the need for antibiofouling efficiency, transparency and non-toxicity are prerequisite surface properties. In this work, seven amphiphilic transparent antifouling coatings have been elaborated using silicone polyether copolymer surfactants mixed in a polydimethylsiloxane-based elastomer matrix. Average molar masses (1.3–11.7 kDa) and molar mass distributions of each surfactant were assessed by pulse-field gradient spin-echo (PGSE) diffusion NMR. Surface and bulk properties of the designed coatings were characterized by measuring their surface roughness (0.03–0.07 μm), Young's modulus (1.4–2.2 MPa) as well as their wetting behavior. Results obtained from different wetting techniques have shown that coatings had initially a low surface free energy (around 20 mJ/m2) and that their surface became amphiphilic in contact with water (from 21 to 42 mJ/m2). Fitting of water contact angle measurements with the so-called O'Brien-Paranjape dynamic surface tension (DST) model enabled the calculation of the surfactant's diffusivities within the PDMS elastomer matrix (ranging from 9.96 × 10−15 to 1.77 × 10−13 m2·s−1) while providing a comprehensive insight on the kinetic interfacial variation of the overall amphiphilic coating. Coatings with the highest rates of water contact angle variation have been shown to positively affect the bovine serum albumin (BSA) protein adsorption.

Microstructural evolution and properties of He-charged a-Si coatings prepared by magnetron sputtering

The introduction of porosity in nanomaterials via magnetron sputtering in helium atmospheres is an interesting strategy for the design of functional materials. Amorphous silicon coatings, with high concentration of He incorporated in the form of overpressurized nano-bubbles, present modified optical properties in comparison with dense coatings of similar composition.In this work, annealing process in He atmosphere from 300 °C up to 1200 °C is performed to evaluate stability after the release of He from the a-Si:He coatings (thickness ∼1700 nm) and to favor matrix crystallization and defect evolution. The work is focused on these effects on the silicon film and its properties. The composition and microstructural evolution of the coatings annealed to temperatures as high as 1200° were investigated by electron microscopy and X-Ray diffraction. Annealing effects on the optical properties and bandgap of the silicon coatings were evaluated by ellipsometry and UV–Vis spectrometry. Helium release from the coating, densification, defects evolution and ordering due to crystallization have a small effect on the refractive index, but cause a significant change in the material band gap from 1.37 eV to 1.80 eV.

Effect of heat treatment on the structure, fracture toughness and oxidation behavior of a silicon coating by atmospheric plasma spraying

Silicon coatings produced by atmospheric plasma spraying are used as bond coat in environmental barrier coatings which protect silicon carbide fiber reinforced silicon carbide composites against water vapor induced corrosion at high temperatures. Silicon coatings exhibit structural defects such as interlamellar boundaries, gaps, pores and microcracks, some of which become pathways for oxygen penetration, leading to internal oxidation of the silicon coating. This study was conducted to reduce the pathways for oxygen penetration by heat-treatment under argon atmosphere and investigate the effects of heat-treatment on the structure, fracture toughness and oxidation behavior of the silicon coating. The results show that the structural defects could be reduced by a heat-treatment at T = 1300 °C, which resulted in a lower mass gain of the coating in the initial cycle in a cyclic oxidation test. The fracture toughness of the coating was significantly decreased by the heat-treatment, which led to the formation of microcracks in the coating in the cyclic oxidation test. As a result, the heat-treated coating exhibited a higher mass gain rate than the as-sprayed coating, leading to that both coatings exhibited almost the same mass gain at the end of the cyclic oxidation test of n = 10 cycles.

Assessing Proton and Hydrogen Permeabilities for Nanoscopic Oxide Coatings Using a Rotating Disk Electrode

The transport of protons and molecular hydrogen (H2) are of relevance to a wide range of electrochemical applications ranging from fuel cells and electrolyzers to sensors and photoelectrochemical cells. One way to modulate the flux of these species to improve device performance such as selectivity and efficiency is to encapsulate electrodes with semi-permeable oxide coatings. [1-3] Thus, knowing the permeabilities of these species within thin oxide layers is of great importance for guiding the design of electrodes and devices. Towards this end, we have employed a modified rotating disk electrode (RDE) set-up to quantify proton and hydrogen permeabilities through sub- 20 nm thick silicon oxide coatings and understand how these transport properties change as a function of the structural and compositional characteristics of the coatings. Oxide coatings were fabricated by both atomic layer deposition (ALD) and photochemical deposition, and their physical and chemical properties characterized by X-Ray Photoelectron spectroscopy and ellipsometry. Based on measurements of the mass transfer limited current density for the hydrogen evolution and hydrogen oxidation reactions, permeabilities were computed. Species permeabilities are furthermore correlated with membrane density and composition, revealing structure-property-performance relationships that can be used to guide the selection of oxide thickness and processing conditions that will optimize performance for an application of interest.

Evolution of the Microstructure and Mechanical Performance of As-Sprayed and Annealed Silicon Coating on Melt-Infiltrated Silicon Carbide Composites.

In this study, silicon coating was deposited on melt-infiltrated SiC composites using atmospheric plasma spraying and then annealed at 1100 and 1250 °C for 1-10 h to investigate the effect of annealing on the layer. The microstructure and mechanical properties were evaluated using scanning electron microscopy, X-ray diffractometry, transmission electron microscopy, nano-indentation, and bond strength tests. A silicon layer with a homogeneous polycrystalline cubic structure was obtained without phase transition after annealing. After annealing, three features were observed at the interface, namely β-SiC/nano-oxide film/Si, Si-rich SiC/Si, and residual Si/nano-oxide film/Si. The nano-oxide film thickness was ≤100 nm and was well combined with SiC and silicon. Additionally, a good bond was formed between the silicon-rich SiC and silicon layer, resulting in a significant bond strength improvement from 11 to >30 MPa.

Microstructures and high temperature oxidation behaviors of AlMo0.5NbTa0.5TiZr high entropy alloys coated by silicon pack cementation

In this study, we fabricated silicon coatings on AlMo0.5NbTa0.5TiZr refractory high entropy alloy using pack cementation for the first time. The growth kinetics of the coating layer were analyzed by considering coating temperature, time, amount of Si, and NaF. The growth coefficient constant and activation energy were determined to be 96,823 µm/h1/2 and 117 kJ/mol, respectively. Microstructural analysis revealed the formation of a protective layer of SiO2 on the specimen surface, which increased its oxidation resistance at 1300 °C. Comparing the uncoated and coated specimens provided insight into the potential use of AlMo0.5NbTa0.5TiZr for high-temperature applications.

Self-assembled multilayer WS2/GO films on amorphous silicon coating for enhancing the lubricating properties

Improving the anti-friction behaviors of silicon-based coatings is of great significance for the lifetime and reliability of the devices. In this work, tungsten disulfide/ graphene oxide (WS2/GO) nanocomposites with different relative contents of GO were firstly prepared by the hydrothermal method. Then 3-(aminopropyl)triethoxysilane (APTES) was employed to establish Si-O-Si links and CNC bonds, enabling WS2/GO films to be assembled on hydroxylated amorphous silicon (a-Si) coatings. Finally, the tribological properties of a-Si assembled with WS2/GO membranes against alumina ceramic (Al2O3) spheres in ambient air were systematically investigated. Through the analysis of the morphology and composition of the friction marks, the reason for the low coefficient of friction (0.12) is the formation of a robust and stabilized WS2/GO membrane at the friction interface, and the lubrication mechanism is attributed to the fact that WS2 nano-sheets extends the layer spacing of GO and promotes the interlayer slip of GO.

Characterization and Control of Residual Stress in Plasma-Sprayed Silicon Coatings on SiC/SiC Composites

In order to reveal the relationship between residual stress in Si layers of SiC/SiC composites and the different parameters used in their preparation, the residual stress of the coating surface was tested using X-ray sin2ψ technology and laser Raman spectroscopy. Then, the Raman shift–stress coefficient (P) and the Raman shift with free stress (ω0) were calculated as −201.41 MPa/cm−1 and 520.591 cm−1 via linear fitting with the least squares method. The results showed that all the as-sprayed Si coatings exhibited tensile stress on the surface, ranging from 53.5 to 65.9 MPa. The parameters of the spraying distance and second gas (H2) flow rate were considered to be the most important for controlling the residual stress on the coating surface. Additionally, the surface tensile stress of the Si layers could be eliminated and even changed into compressive stress by annealing above 800 °C. Furthermore, the residual stress distribution in the cross-section of the Si layers was evaluated using laser Raman spectroscopy. Additionally, the particle characteristics, such as in-flight velocity and temperature, were investigated using a diagnostic system. The results of this research contribute to increasing the understanding and control of residual stress in APS Si bond layers.

Mechanical Strong, Highly Adhesive, Recyclable and Transparent Supramolecular Silicone Coatings with Easy Water/Oil Sliding

Mechanical Strong, Highly Adhesive, Recyclable and Transparent Supramolecular Silicone Coatings with Easy Water/Oil Sliding

Assessing the effect of a thickness gradient on the shear stress profile at the epoxy/silicone interface of thin coatings subjected to transverse shear loads with finite element analyses

ABSTRACT Low surface energy materials are used as foul-release coatings (FRCs) to reduce the forces required to remove biofouling. Previous experiments observed the release behavior of epoxy studs (pseudobarnacles) from silicone coatings with a thickness gradient. The studs were loaded transversely in thick-to-thin and thin-to-thick directions, and the final decohesion always proceeded from the thin to the thick side of the coating. However, trends in the critical transverse forces required for removal were not apparent. In this study, finite element models (FEMs) were created to determine the peak shear stress at the interface of an epoxy stud bonded to a silicone coating with a thickness gradient in response to a transverse load. The effects of the average coating thickness, the thickness gradient of the coating, and the transverse loading direction were determined. At a given average coating thickness, increasing the thickness gradient produced higher peak shear stresses at the interface, which would reduce the critical force required to remove the epoxy stud (i.e., would improve the performance of the FRC). The influence of the increased thickness gradient waned as the average coating thickness increased. Therefore, moderately thin coatings with large thickness gradients would be optimal for FRC performance under transverse loading.

Hybrid Bio-Based Silicone Coatings with Anti-adhesive Properties.

Hybrid polysiloxanes and polysilsesquioxanes grafted with naturally occurring bioactive phytochemicals: eugenol and linalool, were synthesized and investigated with regard to their structure and properties. The two series of materials, differing in the type of inorganic structure and the content of active groups, were coated onto the surface of glass plates, and their antibiofilm activities against bacteria Aeromonas hydrophila were assessed by luminometry and fluorescence microscopy. Bioactivity was correlated with specific properties of the hybrid coatings (chemical structure, surface free energy and adhesiveness). The functionalized polysilsesquioxanes exhibited the most favorable anti-adhesive effects. Cell adhesion after 6 days of incubation, expressed as RLU/cm2, was significantly reduced (44 and 67 for, respectively, Z-E-100 and Z-L-100, compared to 517 for the control glass carrier). The surface stickiness of polysiloxane films deteriorated their anti-adhesion properties, despite the presence of a large amount of bioactive species.

Correlation between Hydrophobicity of Nano-Modified Organic Silicone Coatings and Resistance Against Corrosion in Alternating Environments

Correlation between Hydrophobicity of Nano-Modified Organic Silicone Coatings and Resistance Against Corrosion in Alternating Environments

ПОЛУЧЕНИЕ И ПРИМЕНЕНИЕ ГИДРОФОБНЫХ ПОЛИУРЕТАНОВЫХ КРЕМНИЙСОДЕРЖАЩИХ ПОКРЫТИЙ. ЧАСТЬ 2. (ОБЗОР)

It is well known, that water drops tend to easily flow down from lotus leaves because of low wetting degree. In the first part of the review, we discussed the basic concept of wetting theory and different limits of existing models. The unsolved questions in the theory of wetting did not slow the development of methods of hydrophobic coatings fabrication. At present, coatings with low wetting degree are implemented in different industry fields. However, fabrication of coatings with stable hydrophobic properties is still difficult. That problem is especially serious for highly- and superhydrophobic coatings. The second part of the review describes the methods of fabrication of hydrophobic, highly- and superhydrophobic polyurethane coatings. We briefly mention the chemical reactions, which lead to polyurethanes obtaining, methods of hydrophobic coatings fabrication, and their application fields. Special attention is focused on the analysis of the surface parameters in order to establish general laws for producing hydrophobic, highly-hydrophobic and super-hydrophobic polyurethane silicon coatings

Effect of Microwave-Assisted Curing on Properties of Waterborne Silicone Antifouling Coatings.

Waterborne silicone coatings are prepared in this paper by using silicone emulsion as a film-forming material, γ-methacryloxypropyltrimethoxysilane, and dibutyltin dilaurate as a curing agent and a catalyst, respectively. The corresponding coatings are obtained by controlling different microwave times to accelerate the coating curing. The surface morphology, roughness, surface properties, mechanical properties, and antifouling properties of the coating are studied by laser confocal microscope, contact angle measurement, tensile test, marine bacterial attachment test, and benthic diatom adhesion test. Additionally, the action mechanism of microwaves in the curing process of the coatings is also discussed. The results show that the microwave can greatly reduce the curing time of waterborne silicone coating. It can improve the painting efficiency, the surface roughness of the coating, and the mechanical properties of the coatings. The change in roughness increases the contact angle of the coating, reduces the apparent surface energy, and then improves the antifouling performance. For the coating cured by microwave, with the increase in microwave curing time, the water and diiodomethane contact angles of the coating gradually increase, and the surface energy gradually decreases from about 20 mJ/m2 to 10.8 mJ/m2. With the increase in microwave time, the attachment amount of Navicular Tenera gradually decreases, the removal rate gradually increases, and the removal rate of Navicular Tenera in the coating increases from 15.36% to 31.78%. The bacterial removal rate of the coating can be increases from 11.05% to 22.28% after microwave curing. Microwave-assisted curing is helpful in improving the antifouling and self-cleaning performance of waterborne silicone coatings, showing promising potential applications.

A Design Strategy of Carbon Coatings on Silicon Nanoparticles as Anodes of High-Performance Lithium-Ion Batteries

Carbon coatings are commonly used to improve the performance of silicon anodes by providing a conductive shell that discourages the formation of excess solid/electrolyte interphase (SEI). Lack of understanding on the links between the properties of carbon components, such as mechanical properties and conductivity, and the electrochemical properties limits the advances in development of high-performance silicon–carbon nanocomposites. Herein, uniform carbon coatings with different degrees of graphitization were formed on the surface of silicon nanoparticles using bitumen as a carbon precursor. Analysis of electrochemical impedance spectroscopy (EIS) and distribution of relaxation time (DRT) shows that the carbon coating of higher elasticity and high Li+ diffusion coefficient through the control of carbonizing bitumen coatings on silicon nanoparticles greatly enhanced the electrochemical performance of carbon-coated silicon anodes. The high elasticity provides stable contacts between silicon and carbon coatings and maintains a stable electrode/electrolyte interface (without excessive SEI growth) during long-term cycling. Compared with electronic conductivity, the efficiency of ion diffusion in the carbon coating is found to play an important role in the rate capability of the electrode. This work provides a design strategy to further optimize the performance of the silicon-based anodes.

(Invited) Semipermeable Oxide Coatings for Selective Z-Scheme Photocatalytic Water Splitting

Similar to natural photosynthesis, Z-scheme photocatalytic water splitting relies on two different light absorbing components that are coupled by a redox active mediator that shuttles charge between them. Such a two-absorber system possesses several advantages over single absorber photocatalytic system, including higher theoretical solar-to-hydrogen conversion efficiency, relaxed band alignment requirements, and the potential for inherently safe operation whereby H2 and O2 evolution occur in separated compartments. However, a major disadvantage and challenge for Z-scheme photocatalysis is that the presence of a redox mediator introduces two undesirable back-reactions on top of parasitic H2 oxidation and O2 reduction reactions that can occur in a single absorber photocatalytic system. Previous research efforts have identified the use of semi-permeable oxide coatings as an attractive approach to suppress these thermodynamically favored redox reactions while still permitting the desired water splitting and mediator redox reactions to occur. Here, we present a combined experimental and computational approach based on model thin films that is used to (i) probe the performance limits of oxide-encapsulated photocatalysts, (ii) quantify the effects of coating defects on performance, and (iii) guide the rational design of coatings aimed at maximizing the solar-to-hydrogen conversion efficiency of a target photocatalytic system. This work specifically focusses on the development of silicon and titanium oxide coatings for Z-scheme water splitting based on a Fe(II)/Fe(III) mediator, showing that the best coatings can achieve selectivities > 90 % towards the H2 and O2 evolution reactions over undesired Fe(II)/Fe(III) back reactions. Another key finding from this work is that coating defects can have a significant influence on the performance of encapsulated electrodes, as revealed by scanning electrochemical microscopy (SECM) measurements that were used to locally quantify the parasitic back reaction rates around individual defects to determine their impact on the global selectivity of an encapsulated electrode.

Influence of the atmospheric plasma spraying parameters on the coating structure and the deposition efficiency of silicon powder

Silicon coatings are usually produced by atmospheric plasma spraying (APS) and used as bond coats in environmental barrier coatings. The deposition efficiency (DE) of silicon powders is generally at a low level in APS processes. The reasons for the low DE values of silicon powders have not been sufficiently investigated in the literature. The aim of this study was to investigate in detail the influence of process parameters on the coating structure and deposition efficiency of a silicon powder processed with APS. A silicon powder with a size distribution of f = –53 + 15 µm was sprayed using a three-cathode plasma generator to produce coatings. The parameters such as plasma gas type, plasma gas flow rate and current intensity were varied widely. Accordingly, the power of the plasma generator increased from P = 19.4 to 51.3 kW, which allowed different melting and evaporation degrees of the powder. Particle velocities and temperatures were measured using a particle diagnostic method. The coatings were investigated in terms of their surfaces and structures using electron scanning microscopy (SEM). The porosities of the coatings were measured using an image analysis system. The deposition efficiency of the processed powder was determined. The results show that the used parameters led to high particle velocities in a range of about vp = 270–360 m/s. High particle temperatures of Tp = 2,650–3,390 °C were determined. The coating porosity varied from Φ = 2% to Φ = 15%. The porosity value of Φ = 2% is significantly lower than the values reported in the literature. The deposition efficiency of the powder changed from DE = 1.5% to DE = 28%. The value of DE = 28% is about 40% higher than the values reported in the literature. The strong grit-blasting effect was the main reason for the lowest DE value of DE = 1.5%. The strong evaporation effect was the main reason for the second lowest DE value of DE = 11.1%. Numerous melted particles and semi-melted particles splashed upon impact with the substrate, resulting in silicon melt loss. In addition, solid cores of semi-molten particles could bounce off, which also resulted in silicon loss. Splashing and bouncing were the main factors affecting DE for the parameter sets with DE values ranging from 18.7% to 28%.

Application of Functional Nanomaterials in Process Design and Art Design

Coating is a kind of decorative material with decorative function, protection function, adjustment function, and various special functions. In recent years, with the continuous improvement of people’s material living standards, the relationship between environmental protection and health, environment and future development, and environment and nature has been increasingly deepened. The coating industry has developed rapidly in recent years. Nanomaterials have received much attention for their unique physical and chemical properties. Using nanomaterials to modify traditional coatings is a way to rapidly improve the development of the coating industry. In this paper, the properties and preparation technology of nano-TiO2 and nano-ZnO are reviewed, the photocatalytic mechanism of TiO2 and ZnO nanomaterials is discussed, and the two are applied in traditional coating systems to develop nanocomposite coatings. The nano-TiO2 and nano-ZnO components were added to the pure acrylic and silicon acrylic coatings according to a certain proportion to explore the influence of different proportions of nanomaterials on the performance of the above coatings. The results showed a significant improvement in the main performance of the coating at the addition amount of 0.4%. Overall, the modification effect of the nanocomposite component was the most significant, and the nano-ZnO was better than the nano-TiO2, and silicon propylene paint is better performance than pure propylene paint. The ratio of coating pairs prepared in the experiment was 0.98, the brush resistance number was 1990, the adhesion level was level 1, and the reflectance was decreased by 8.58%. The introduction of functional nanomaterials can significantly improve the contrast ratio, scrub resistance, and adhesion of coatings.

Investigating the weathering performance of epoxy silicone nanocomposite coatings containing various loadings of Glycidoxypropyltrimethoxysilane-modified Zinc oxide nanoparticles

This research presents the modification of ZnO nanoparticles by Glycidoxypropyltrimethoxysilane (GPTMS) to produce hybrid nanostructured additives to improve the weathering resistance of epoxy silicone coatings. The modified ZnO nanoparticles were incorporated into epoxy silicone coatings at different loading dosages. The coatings were then weathered in an accelerated weathering chamber and removed after specific intervals (0, 500, and 1000 h) for further characterization. The effect of different loadings of modified ZnO nanoparticles (0.1, 0.5, and 1 wt%) on the weathering resistance of epoxy silicone coatings was studied using SEM, AFM, FTIR, and contact angle measurement, UV–visible spectroscopy, optical microscope, gloss, Vickers hardness, and gonio-spectrophotometer. All results showed that the addition of modified nanoparticles effectively promoted (6 times improvement based on carbonyl index) the weathering resistance of the epoxy silicone coating. It was also concluded that the coatings filled at a low level (0.1 wt%) of GPTMS-modified ZnO provided much more superior weathering performance than those loaded with higher filler content (0.5 and 1 wt%). It was explained by the more crosslinked network formed and the fine distribution of modified filler within the matrix at low filler content.

The impact of surfactants on the properties of electroless Ni–P–SiC coatings

The development and properties of electroless nickel silicon (Ni–P–SiC) coatings on steel substrates with different surfactants were investigated in this study. Different surfactant additives (anionic, cationic, and nonionic) were used to prevent the agglomeration of SiC nanoparticles in the coating bath. Their effect on the deposition rate, surface roughness, microhardness, and corrosion resistance of Ni–P–SiC coatings was investigated in this study. XRD, SEM, and EDS analysis was performed to observe the crystal structure, morphology, and chemical composition of the deposit. Potentiodynamic polarization tests, stylus surface measurement devices, and Vickers microhardness testers were used to explore the corrosion behavior, surface roughness, and microhardness of the coatings. The presence of the three surfactants at a 0.6 g/L concentration significantly influences the characteristics of the coatings. The maximum number of SiC nanoparticles was homogeneously distributed in the Ni alloy in the presence of a cationic surfactant. The coating developed from the cationic surfactant bath exhibited the highest microhardness, corrosion resistance, deposition rate, and smooth surface identified in the coating developed from the cationic surfactant bath.