Siloxane Coatings Research Articles

Nonleaching Biocidal N-Halamine-Functionalized Polyamine-, Guanidine-, and Hydantoin-Based Coatings.

Fibrous materials with inherent antimicrobial properties can help in real-time deactivation of microorganisms, enabling multiple uses while reducing secondary infections. Coatings with antiviral polymers enhance the surface functionality for existing and potential future pandemics. Herein, we demonstrated a straightforward route toward biocidal surface creation using polymers with nucleophilic biguanide, guanidine, and hydantoin groups that are covalently attached onto a solid support. Biocidal poly(N-vinylguanidine) (PVG) and poly(allylamine-co-4-aminopyridine-co-5-(4-hydroxybenzylidene)hydantoin) (PAH) were introduced for coating applications along with commercially available polyvinylamine (PVAm) and poly(hexamethylene biguanide) (PHMB). Nonleaching coatings were created by first fabricating bifunctional siloxane or isocyanate precursor coatings on the cotton, nylon-cotton, and glass fiber fabric, followed by the polymer attachment. The developed grafting methods ensured the stability of the coating and the reuse of the material while maintaining the biocidal properties. Halogenation of polymer-coated fabric was conducted by aqueous solutions of sodium hypochlorite or in situ generation of hypobromous acid (HOBr), resulting in surfaces coated by N-halamines with high contents of active > N-Cl or > N-Br groups. The polymer-coated fabrics were stable in multiple laundry cycles and maintained hydrophilic character after coating and halogenation. Halogenated polymer-coated fabrics completely inactivated human respiratory coronavirus based on a contact-killing mechanism and were shown to be reusable after recharging with bromine or chlorine.

Evaluation of the effectiveness and durability of commercial non-stick coatings

In this study, four commercial non-stick coatings (two fluoropolymer and two ceramic) were characterized by micrography, Raman spectroscopy and energy dispersive X-ray spectroscopy (EDX). A pancake batter was then baked on coated aluminum substrates. In a first test, 90 consecutive baking cycles were performed on each coated specimen. In a second test, the coatings were abraded by sanding, followed by 30 baking cycles. In both cases, take-off pressure was evaluated to extract the pancake model, as well as water sliding angle, surface roughness and surface damage. The results have shown that perfluoroalkoxyalkane (PFA) and polytetrafluoroethylene (PTFE) were the most effective in terms of pull-off pressure (<3 kPa) versus ceramic siloxane coatings with values between 15 and 34 kPa after 90 firings. In the different experimental stages, a positive correlation between wettability and detachment force was observed, especially for fluoropolymer coatings. However, surface roughness did not strong correlate with the pull-off force, low values did not correlate with low values of pull-off force and vice versa. This paper proposes an objective and simple coating evaluation procedure for industrial environments. Although ceramic sol-gel coatings show potential, there is a need to improve their non-stick capability to bring them on par with traditional solutions.

Practical Application of Selected Functional Organosilicone Polymers

The available information concerning the preparation and properties of modifying siloxane coatings on the surface of fibrous materials, as well as a number of other functional silicone polymers for hydrophobization of fibers, textiles, leather, building materials, creation of adhesive compositions, and other practically valuable silicone products has been generalized.

Vapor–Gas Deposition of Polymer Coatings on Metals from Azeotropic Solutions of Organosilanes

The mechanism of the vapor–gas deposition of vinyltrimethoxysilane (VS) and ethylene glycol (EG) from azeotropic solutions is investigated, which allows a reduction of the evaporation temperature of the components of working mixtures. The need for such studies is associated with the development of a new direction in the technology of vapor–gas deposition of polymer coatings. Methods have been developed for monitoring the chemical composition of working solutions in evaporators using optical spectroscopy, which makes it possible to calculate the partial pressures of vapor-phase components. Based on these studies, compositions of working solutions are proposed that allow the equalization of the partial pressures of the components of working mixtures with a large difference in the boiling point. With the aid of vapor–gas deposition, siloxane coatings on low-carbon steel were obtained, the protective properties of which exceeded the treatment with volatile inhibitors of the adsorption type by two to three orders of magnitude. A new method of vapor–gas deposition of non-volatile powder inhibitors on metals is proposed. Chemical compositions of siloxane coatings were determined using XPS, and mechanisms of interaction of VS with the polymerization promoters ethylene glycol and 1-hydroxy ethylidene-1,1-diphosphonic acid (HEDP) were proposed.

Fucoidan-Containing, Low-Adhesive Siloxane Coatings for Medical Applications: Inhibition of Bacterial Growth and Biofilm Development.

The deposition of low-adhesive siloxane coatings is a current trend for the non-toxic control of bacterial growth and biofilm formation. Total elimination of biofilm formation has not been reported so far. The aim of this investigation was to study the ability of a non-toxic, natural, biologically active substance, such as fucoidan, to inhibit bacterial growth on similar medical coatings. The fucoidan amount was varied, and its impact on the bioadhesion-influencing surface characteristics, as well as on bacterial cell growth, was investigated. The inclusion of up to 3-4 wt.% brown algae-derived fucoidan in the coatings increases their inhibitory effect, more significantly on the Gram-positive bacterium S. aureus than on the Gram-negative bacterium Escherichia coli. The biological activity of the studied siloxane coatings was ascribed to the formation of a low-adhesive, biologically active surface top layer consisting of siloxane oil and dispersed water-soluble fucoidan particles. This is the first report on the antibacterial activity of fucoidan-containing medical siloxane coatings. The experimental results give reason to expect that relevantly selected, natural biologically active substances can be efficient in the non-toxic control of bacterial growth on medical devices and, as a result, medical device-associated infections.

The Effect of Curing Temperature and Thickness of Polybutyl Methacrylate Siloxane Coatings on the Corrosion Protection of Structural Steel S355

This study aimed to determine the effects of coating thickness and curing temperature on the properties of a polybutyl methacrylate-siloxane coating deposited on structural steel S355. First, the thermal properties of the sol as a function of temperature were investigated using thermogravimetric analysis coupled with mass spectrometry and differential scanning calorimetry. After coating deposition on structural steel S355 using a dip-coating process, the coating composition and porosity were evaluated using Fourier transform infrared spectroscopy and photothermal beam deflection spectroscopy. In the second part, coating thickness, topography, and corrosion properties were studied as functions of withdrawal rate during deposition. The corrosion properties of variously prepared coatings were evaluated using electrochemical impedance measurements in 3.5 wt.% NaCl and salt spray testing according to the ASTM B117 standard. An elevated curing temperature (at 150 °C) of the polybutyl methacrylate siloxane sol-gel coating impairs greater crosslinking and lower porosity, while the optimal thickness of 4 μm is achieved with the appropriate withdrawal rate to obtain a homogeneous, defect-free surface. Under these optimal conditions, the protection of structural steel against corrosion in a chloride environment lasting for more than 6 months can be achieved.

Slippery Alkoxysilane Coatings for Antifouling Applications.

Herein, we report the wettability and antifouling behavior of a range of different siloxane coatings on plastic and glass substrates. The films investigated are prepared using trimethoxysilane precursors with different alkyl chain lengths (1-18 C atoms) in order to study how the nature of the hydrophobic group affects the different parameters used to characterize wettability (contact angles, sliding angles, and contact angle hysteresis). Atomic force microscopy analysis shows that the coatings possess low surface topography [root mean squared roughness (rms) < 50 nm] and are highly transparent as studied using UV-vis spectroscopy. The sliding properties of H2O, CH2I2, methanol, and ethylene glycol were observed to be strongly influenced by the chain length of the alkoxysilane precursor used. The coatings formed from the longer chain analogues show comparable water sliding angles to superhydrophobic surfaces. These coatings show similar performance to analogous alkoxysilane coating-bearing fluorinated groups, indicating that they could act as viable environmentally friendly alternatives to some of the fluorinated films that have been widely adopted. Furthermore, these surfaces are highly durable toward common forms of abrasion and are observed to show low adhesion toward synthetic feces, indicating that their utility extends further than repelling liquids alone. Consequently, these coatings could show promise for potential use in applications in the medical sector where fouling by biological mixtures leads to an unsustainable use of materials.

Fabrication, Characterization, and Corrosion Protection of Siloxane Coating on an Oxygen Plasma Pre-treated Silver-Copper Alloy

In this study, siloxane has been used for the protection of metal artifacts from corrosion in the form of transparent barrier coating films because of their good adhesion to the metal substrate. The effect of oxygen plasma pre-treatment on the adhesion properties of the siloxane thin film on the silver-copper alloy substrate was investigated. Radiofrequency plasma-enhanced chemical vapor deposition (RF-PECVD) was used for the deposition process. Surface identification and characterization of the deposited films were carried out using Scanning Electron Microscopy coupled with energy-dispersive x-ray spectroscopy (SEM–EDX) and Fourier-transform infrared spectroscopy (FT-IR). Surface topography and roughness were investigated by atomic force microscopy (AFM). The hydrophobic characteristic was measured by water contact angle measurement (WCA). The film thickness was evaluated using a spectroscopic ellipsometer (SE). Colorimetric measurement (CM) was used to evaluate changes in the appearance of the surface following the PECVD deposition of the SiO2 protective layer. The corrosion protection ability of siloxane films for metal substrates as a function of RF power and gas feed composition was examined by the electrochemical impedance spectroscopy (EIS) technique. It was found that the deposited film improved the protective efficiency for samples from 55.29 to 92.93%. Besides, after the oxygen plasma pretreatment step, the film showed better corrosion resistance of the tested samples.

Effect of Coating Thickness on the Atomic Oxygen Resistance of Siloxane Coatings Synthesized by Plasma Polymerization Deposition Technique

Atomic oxygen in the low Earth orbit (LEO) environment is highly oxidizing. Due to the high flight speed of spacecraft, the relative kinetic energy of high-flux atomic oxygen bombarding the spacecraft surface can reach up to about 5 eV. Therefore, atomic oxygen is one of the most dangerous space environment factors in LEO, which seriously affects the safe operation and service life of spacecraft in orbit. In order to meet the requirements for the high reliability and long lifetime of spacecraft, effective protection measures must be taken on their sensitive surfaces. Siloxane is a coating with an organic–inorganic hybrid structure. Compared with SiO2 and other inorganic atomic oxygen protective coatings, it has better flexibility and is better at anti-atomic oxygen performance. In this paper, the plasma polymerization deposition technique was used to prepare large-area siloxane coatings on different substrates with different thicknesses for improving atomic oxygen resistance by optimizing the process parameters. The thickness of the coating was measured by different methods, and the results showed that the thickness distribution was consistent. By observing the surface morphology of the coating, it was uniform and compact without obvious defects, so the uniformity of large-area coating was also ideal. The adhesion and heat/humidity resistance of siloxane coatings were examined by pull-off testing and damp-heat testing, respectively. The results showed that the siloxane coatings with a thickness of about 400 nm exhibited better physical properties. At the same time, the ground simulation testing of atomic oxygen confirmed that siloxane coatings with a thickness of 418 nm presented the best performance of atomic oxygen resistance. The atomic oxygen erosion yield of siloxane coatings with a thickness of 418 nm was as low as 5.39 × 10−27 cm3/atoms, which was three orders of magnitude lower than that of the uncoated Kapton substrate and presented a good anti-atomic oxygen performance. Meanwhile, it has also successfully passed the damp-heat test. The coating thickness is only several hundred nanometers and does not increase the weight of the spacecraft, which makes it a relatively ideal LEO atomic oxygen protection material. Furthermore, a possible mechanism was proposed to explicate the physicochemical process of atomic oxygen attacking the coating materials.

Long-term effect of weather in Dfb climate subtype on properties of hydrophobic coatings on sandstone

Hydrophobic poly(alkyl siloxane) coatings (pure and containing 0.5 wt% of nano-ZnO) were applied by spraying on sandstone. Coated (S/P and S/PZnO) and uncoated (S) samples were characterized and exposed to weather for 545 days in Ostrava, Czech Republic, an industrial city having persistently high concentrations of particulate matter in air (PM10 ≈ 20±10 μg/m3) and belonging to the Dfb climate subtype. Despite the more distinct final colour change of S/P and S/PZnO front faces, the differences between front and back faces were significantly smaller (ΔE*F–B values of ∼3.7 and ∼3.1 for S/P and S/PZnO, respectively) compared to S (ΔE*F–B ≈ 7.7). Correlations of colour changes with meteorological data revealed effect of relative air humidity, total precipitation, and concentration of particulate matter. Static contact angle (initial values of 137° and 142° for S/P and S/PZnO, respectively) remained >120° during the experiment, and the coatings effectively prevented the falling rainwater to soak into the sandstone. The high hydrophobicity was not accompanied by closure of pores. Despite a decrease in Zn content, no algae was observed on S/PZnO during the experiment. On S and S/P samples, the algae was found after 473 days.

Hydrophilic Modified Siloxane Coatings

Hydrophilic Modified Siloxane Coatings

Vapour Phase Deposition of Thin Siloxane Coatings on the Iron Surface. The Impact of the Layer Structure and Oxygen Adsorption on Corrosion Stability

The mechanism of iron corrosion protection by thin siloxane films was clarified. Quartz crystal microbalance technique (QCM) was applied to control the vapour phase deposition of alkoxysilanes and the formation of thin siloxane films. It was shown that the addition of water vapour increased the thickness of the grafted siloxane films. Crystal-like films spontaneously grow to 10–16 monolayers at 100% RH of Ar flow due to the catalytic effect of the surface. X-ray photoelectron (XPS) and Auger spectroscopies analysed the thin siloxane films and Scanning Kelvin Probe (SKP) showed the formation of iron-siloxane bonds passivating the iron surface. The films showed high hydrophobicity and corrosion inhibition in humid air contaminated by sulphur dioxide. Thick films were less ordered, hydrophilic and accelerated the corrosion of iron. For corrosion protection, the presence of oxygen in the atmosphere is extremely important. In a wet Ar atmosphere, contaminated by sulphur dioxide, the surfaces are not stable and quickly corroded. Oxygen adsorption stabilizes the surface oxide film that correspondingly preserves the anchoring iron-siloxane bonds and enables corrosion protection by the coating.

Preparation of siloxane coatings under microwave irradiation

Preparation of siloxane coatings under microwave irradiation

Development of Siloxane Coating with Oxide Fillers for Kesteritic (CZTS) Photovoltaic Systems

Photovoltaic systems (PV) based on Cu2ZnSn(S, Se)4 (CZTS) solar cells have demonstrated efficiency and high performance. According to the results of comparative studies, the kesterite structure has proven to be ecologically safe and less expensive than other photovoltaic systems. The goal of the present study was to design a disposable high-temperature transparent electrical insulating coating to cover metal plates for photovoltaic devices based on CZTS. The solution was to replace electrically conductive metallics dispersed in a high-temperature siloxane coating with phonon thermal conductivity ceramic particles. Properties of the obtained coating were investigated using different methods. A mathematical model of thermal processes in the film during heating was also developed. For the control sample and the sample with a heat-conducting filler, a quantitative ratio of thermal conductivity was obtained. The research results confirmed the necessary properties of the coating, including resistance to short-term exposure to high temperatures during the synthesis of kesterite.

Anti–corrosive siloxane coatings for improved long–term performance of supercapacitors with an aqueous electrolyte

This paper reports on the impact that the corrosion of the stainless steel current collectors has on the performance fade of a symmetric, carbon/carbon electrochemical capacitor, operating with an aqueous electrolyte (1 M Na2SO4). The results obtained by applying electrochemical ageing protocols (voltage–holding tests) confirm that the current collector of the positive electrode undergoes tremendous degradation during 200 h in the charged state. To prevent the detrimental impact of the corrosion, a hydrophobic siloxane coating has been successfully applied. In the case of siloxane–protected current collectors that are subjected to identical ageing protocols, no significant deterioration in the electrochemical capacitor performance was observed. The siloxane coating reduces the electrochemical corrosion rate of 316 L stainless steel significantly, as the potentiodynamic polarization tests and the electrochemical impedance spectroscopy results show. The presence of the coating is demonstrated by the water contact angle measurements, atomic force microscopy and energy–dispersive X–ray spectroscopy analysis.

Development of Photo-sensitive Siloxane Coatings with High Light-diffusion

Development of Photo-sensitive Siloxane Coatings with High Light-diffusion

Controlled Silanization: High Molecular Regularity of Functional Thiol Groups on Siloxane Coatings.

A comparative study on deposition and molecular regularity of two organosilanes, i.e., commercially available (3-mercaptopropyl)trimethoxysilane (MPTMS) and newly developed mercaptopropylsilatrane (MPS), was conducted in this work. MPTMS and MPS were applied to modify silicon surfaces to characterize their deposition kinetics, surface morphology, thickness, and elemental composition and the reactivity of thiol end groups based on gold-thiol and thiol-ene chemistries. MPS possesses a tricyclic caged structure and a transannular N → Si dative bond, making it chemically stable and controllable to avoid fast hydrolysis and aggregation in solution. The results indicate that MPS allows faster deposition and better formation of thin and homogeneous films than MPTMS. More importantly, the functional thiol groups on MPS coatings enable immobilization of a large amount of gold nanoparticles and effective thiol-ene photopolymerization with zwitterionic sulfobetaine acrylamide. Postmodification on silanized surfaces with MPS endows excellent plasmonic and antifouling properties, potentially leading to valuable applications to biosensing and biomaterials. The work demonstrated the feasibility and applicability of the functional silatrane molecule for surface silanization in a controlled manner.

Полисилазаоксаны и клеевые композиции на их основе

The polymer formation proceeding with the participation of cardosilazaoxane organosilicon oligomers are considered. By the interaction of cardocyclic silazaoxanes with organosiloxane diols, new types of organosilicon oligomers are synthesized. They are capable to form elastic spatial-netted structures due to polymerization processes with the discovery of cyclic siloxane fragments without isolation of low molecular weight by-products. The influence of temperature and the silazaoxane: diol ratio on the nature of the products formed is studied. It was established that at 120-130 °C soluble oligomers of cyclolinear structure are formed, which are structured at 180-190 °C, with the most dense network structure being formed when the silazoxane: diol ratio is close to equimolar; a certain excess of hydroxyl groups at the final stage of polymerization leads to the association of the released ammonia with OH end groups and the formation of nucleophilic particles at the ends of the polymer chains – siloxanolate anions, possibly initiating structuring. The formation of regular three-dimensional structures – polysilazaoxanes, initiated by siloxanolate anions without the use of a special catalyst, is a new approach to the creation of adhesive compositions. In this case, in contrast to catalytically cured siloxane analogues, the resulting cross-linked polymer structures exhibit enhanced adhesion to the substrate material. Such polysilazaoxane oligomers can be used: a) as a basis for adhesives, only thermal effects and compounds containing siloxane films and coatings with various metals and characteristics can be used as a catalyst; b) for hydrophobic impregnation of textile materials and leather half-finished products, since this is clearly ammonia, which does not have a destructive effect on them.

FIMEC Test to Evaluate the Water Uptake of Coated and Uncoated CFRP Composites.

This study focuses on the application of the FIMEC (flat-top cylinder indenter for mechanical characterization) indentation test to evaluate the effect of water uptake on the mechanical properties of high-performance materials, in particular CFRP (carbon fibre reinforced polymer) composites. Coated and uncoated samples were analyzed. Silicon-based and siloxane coatings were formulated and applied to CFRP to reduce the moisture absorption of the material. The FIMEC test was adopted to study the reduction of the stiffness of CFRP plates for different ageing in water. The evolution of mechanical properties is reported as a function of the water uptake. IR analyses and weight variation measures were used as supporting data. Experimental results show that the FIMEC test is suitable to assess the stiffness reduction due to the aging in water and to identify coatings able to minimize the water uptake.

Photoactive and hydrophobic nano-ZnO/poly(alkyl siloxane) coating for the protection of sandstone

Poly(alkyl siloxane) containing photoactive nano-ZnO (0.5 wt%) has been studied as a protective coating of glauconitic sandstone. Effect on visual appearance, hydrophobicity, porosity, water absorption/evaporation, and self-cleaning ability of the sandstone was measured. The results were evaluated in comparison with uncoated and poly(alkyl siloxane)-coated sandstone. Static contact angle of water reached 89° ± 3° and 128° ± 2° for poly(alkyl siloxane) and nano-ZnO/poly(alkyl siloxane) coating, respectively. Poly(alkyl siloxane) and nano-ZnO/poly(alkyl siloxane) coatings led to increased reduction in water absorption (>50%) for ∼18 h and ∼8 h, respectively, compared to the uncoated sandstone. The shorter time is compensated by self-cleaning ability: photodegradation of methylene blue on the nano-ZnO/poly(alkyl siloxane) coating after 5 h of UV irradiation was observed. This coating is a promising candidate for practical use in sandstone monuments protection.