Fluoropolymer Coatings Research Articles

Possible mechanisms for adverse effects on zebrafish sperm and testes associated with low-level chronic PFOA exposure

Perfluorooctanoic acid (PFOA), which is widely used during the manufacturing of fluoropolymer coatings and polytetrafluoroethylene, is now a widespread pollutant in the environment and within the human body. This study used zebrafish, an aquatic model species, to investigate how low levels of chronic PFOA exposure affect the reproductive system. The results of the experiments in which zebrafish were exposed to 414 ng/L or 4140 ng/L for 60 days showed a variety of adverse effects on testicular tissue and sperm, including dose-dependent changes in plasma estradiol and testosterone levels, various sperm malformations, decreased sperm motility and concentration, and PFOA-induced oxidative stress and testicular damage with increased rates of apoptosis. In addition, offspring of the zebrafish that had been exposed to PFOA were characterized by increased malformation and mortality. Subsequent transcriptional analyses of the male gonads revealed the significant activation of oxidative stress bioprocesses and immuno-inflammatory signaling pathways, along with the dysregulation of reproductive bioprocesses. In conclusion, low-level chronic exposure to PFOA affects both the reproductive performance of adults and the development of offspring; the mechanisms for these adverse effects involve alterations in several molecular pathways that may be involved in PFOA-induced oxidative stress and reproductive abnormalities. The presented data can be used to assess the ecotoxicity of PFOA to the male reproductive system at environmentally-relevant concentrations.

Thermally Stable Perovskite Solar Cells with Fluoropolymer Coating

Halide perovskites are promising as the light absorbers of solar cells with efficient solar power conversion. However, why the degradation of perovskite solar cells (PSCs), especially at high temperatures, happens has not been completely understood to date. Herein, it is shown that evaporation of 4‐tert‐butylpyridine (4‐tBP) from the hole transport layer (HTL) of 2,2',7,7'‐tetrakis(N,N‐di‐p‐methoxyphenylamino)‐9,9'‐spirobifluorene (spiro‐OMeTAD) is one of possible degradation mechanisms in PSCs at a high temperature of 85 °C. In fresh PSCs, the chemical doping of the spiro‐OMeTAD HTL with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is not so efficient because of the formation of a LiTFSI:4‐tBP complex in the HTL. When PSCs are placed at 85 °C, 4‐tBP gradually evaporates from the HTL, resulting in the dissociation of the LiTFSI:4‐tBP complex. This 4‐tBP evaporation enhances the chemical doping of spiro‐OMeTAD by LiTFSI and makes the hole transport level of the spiro‐OMeTAD HTL deeper, thereby impeding hole extraction at the perovskite/spiro‐OMeTAD/Au interfaces. Herein, the 4‐tBP evaporation by covering PSCs with a fluoro‐polymer CYTOP layer, significantly improving the high‐temperature durability of PSCs, is suppressed. The basic understanding obtained in this study would help promote the spread of more thermally durable PSC products in the future.

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.

New approaches for creating effective combined printed circuit boards on thermally conductive substrates with polyimide dielectrics

New approaches to manufacturing improved combined boards on aluminum bases with various thin polyimide dielectrics, including thermally conductive ones, foiled by copper or aluminum foil have been proposed.&#x0D; Design and technological solutions and methods for manufacturing combined printed circuit boards on aluminum bases using industrial thin thermally conductive polyimide dielectric films with fluoropolymer coatings with thermal conductivity from 0,12 to 0,46 W/(m·K) have been developed. Design and technological solutions and methods for manufacturing combined printed circuit boards on thermally conductive aluminum bases using adhesive-free copper-polyimide and aluminum-polyimide lacquer foil dielectrics with thermal conductivity of varnish polyimide layers from 0,12 up to 1,0 W/(m·K) and more have been developed.&#x0D; Main chemical, mechanical, electrical end thermal properties of various types of experimental combined printed circuit boards on aluminum bases with thin polyimide dielectrics for use in electronic modules and printed circuit assemblies (including with using Chip-on-board and Chip-on-flex technologies for assembling) have been studied.

Oil–Water Separation on Hydrophobic and Superhydrophobic Membranes Made of Stainless Steel Meshes with Fluoropolymer Coatings

In this work, membranes were synthesized by depositing fluoropolymer coatings onto metal meshes using the hot wire chemical vapor deposition (HW CVD) method. By changing the deposition parameters, membranes with different wetting angles were obtained, with water contact angles for different membranes over a range from 130° ± 5° to 170° ± 2° and a constant oil contact angle of about 80° ± 2°. These membranes were used for the separation of an oil–water emulsion in a simple filtration test. The main parameters affecting the separation efficiency and the optimal separation mode were determined. The results reveal the effectiveness of the use of the membranes for the separation of emulsions of water and commercial crude oil, with separation efficiency values that can reach over 99%. The membranes are most efficient when separating emulsions with a water concentration of less than 5%. The pore size of the membrane significantly affects the rate and efficiency of separation. Pore sizes in the range from 40 to 200 µm are investigated. The smaller the pore size of the membranes, the higher the separation efficiency. The work is of great economic and practical importance for improving the efficiency of the membrane separation of oil–water emulsions. It lays the foundation for future research on the use of hydrophobic membranes for the separation of various emulsions of water and oil products (diesel fuel, gasoline, kerosene, etc.).

Research in fluorinated block copolymer/polystyrene blends with durable antifouling properties based on chain-entanglement

The durability of antifouling properties is always the problem in fluoropolymer coatings with low surface energy. The bonding between fluorinated polymers of the coating and substrate depends greatly on the penetration with little entanglement in their segments. Segment entanglement is an important factor for the bonding between two polymers, which can be obtained through melt-blending process. In order to create better entanglement and compatibility in fluoropolymers and polystyrene (PS), a kind of block polymers made from pentafluorostyrene (PFS) were prepared by atom transfer radical polymerization (ATRP), with both perfluoroalkyl ethyl group (Fx-group) and alkyl group (Cx-group) on the side. Each side-group played its role respectively through a melt-blending process. At that melting temperature, Fx-group could easily move and aggregate to the surface, and Cx-group would entangle and blend with PS as well. Accordingly, the blends had the surface contact angle of 110.60°(water) and 40.48°(n-dodecane) exhibiting a good antifouling property. Besides, the glass transition temperature (Tg) of the block polymer changed from two peaks to one, after being blended with PS, indicating that block copolymers were completely compatible with PS at the content of 5%wt to 15%wt. It also has been proved by Scanning Electron Microscope (SEM) that the melt-blending process of blends enhanced with more possible entanglement, as the carbon number of Cx-group increased. Therefore, the blends with longer alkyl side-group displayed more durable antifouling properties than coating process, after being polished 160 times by 800-mesh sandpaper or being immersed in ethanol for 96 h. This work will probably provide a new strategy as a substitute of coating process to achieve more durable antifouling properties in general polymer materials.

DEPOSITION OF HYDROPHOBIC FLUOROPOLYMER COATINGS ON A PLASMA-TREATED STAINLESS STEEL SURFACE

A stainless steel surface was treated with a glow discharge plasma. As a result of surface treatment, micro- and nanostructures were obtained. The surface roughness of the samples was increased. Thin fluoropolymer coatings were deposited on treated and untreated surfaces using the hot wire chemical vapor deposition (HWCVD) method. The structure of the obtained samples was studied by scanning and atomic force microscopy. Wetting properties were measured for all samples obtained. It has been shown that pretreatment of the surface before the deposition of fluoropolymer coatings makes it possible to increase the hydrophobicity of the final surfaces. Tests of coatings carried out using an ultrasonic cleaner have shown that plasma pretreatment before deposition and subsequent annealing after deposition make it possible to obtain stable coatings with stable hydrophobic properties.

Improving Anti-Humidity Property of a SnO2-Based Chemiresistive Hydrogen Sensor by a Breathable and Hydrophobic Fluoropolymer Coating.

Metal-oxide-based chemiresistive hydrogen sensors exhibit high sensitivity, long-term stability, and low cost and have been extensively applied in safety monitoring of H2. However, the sensing performances are dramatically affected by the water vapor, resulting in reduced response value and increased response/recovery time. To improve the anti-humidity property of sensors, coating the breathable and hydrophobic membrane on the surface of the sensing film is an effective strategy. In this work, the poly[4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole-co-tetrafluoroethylene] (Teflon AF-2400) was dip-coated on the surface of SnO2 in a commercial hydrogen sensor (TGS2615) as a breathable and hydrophobic membrane. For safety, He instead of H2 was used to test the gas permeability of membranes. The Teflon membrane shows a high He permeability of up to 40,700 Barrer and an excellent He/H2O selectivity of 99. Moreover, Teflon shows high processability to form a defect-free coating on the rough surface of the sensing film and high chemical stability under the operando condition of the sensor. Thus, the Teflon-modified sensor possesses excellent selectivity with a value of 5, and the resistance is stable at 10,554 ± 3% Ω for 20 days in 80% RH. The modified sensor shows an improved anti-humidity property with a 75% response to 200 ppm H2 at 80% RH and has a low coefficient of variation value of 7.23% that shows advances than other reported sensors modified by coatings. The commercially available Teflon and the simple coating technology make the strategy easily scale up and show promising applications.

Analysis of Wear Phenomena Produced by Erosion with Abrasive Particles against Fluoropolymeric Coatings.

To date, PTFE, PFA, and FEP-based fluoropolymer coatings have proven unbeatable in many services due to their excellent chemical inertness, very low wettability, thermal resistance, high non-stick properties, and good applicability. In use, these coatings usually suffer service cycles with consequent deterioration, and it is of great interest to determine the intensity and type of wear caused in addition to the deterioration that occurs in their properties. In this work, the response of three polymeric coatings of interest applied to aluminum substrates, after being subjected to the action of abrasive particles of aluminum corundum, glass, and plastic projected under pressure, has been studied. During the application of a given wear cycle, the hardness, surface roughness, surface texture, and thickness of the coating have been measured, in addition to the slip angle and surface transmittance to analyze the evolution of each type of coating. The results allowed a concise evaluation of the performance of three fluoropolymeric coatings of great interest, differentiating the induced erosive wear phenomena and contributing complete information to facilitate the correct selection for users with practical application purposes and as a basis for future research work focused on advancements in this field.

Effect of Photoconversion Coatings for Greenhouses on Electrical Signal-Induced Resistance to Heat Stress of Tomato Plants.

The use of photoconversion coatings is a promising approach to improving the quality of light when growing plants in greenhouses in low light conditions. In this work, we studied the effect of fluoropolymer coatings, which produce photoconversion of UV-A radiation and violet light into blue and red light, on the growth and resistance to heat stress of tomato plants (Solanum lycopersicum L.). The stimulating effect of the spectrum obtained as a result of photoconversion on plant growth and the activity of the photosynthesis process are shown. At the same time, the ability to withstand heat stress is reduced in plants grown under a photoconversion coating. Stress electrical signals, which normally increase resistance, in such plants have a much weaker protective effect on the photosynthetic apparatus. The observed effects are apparently explained by a decrease in the concentration of H2O2 in plants grown using photoconversion technologies, which leads to a shift in the development program towards increased productivity to the detriment of the protective function. Thus, when using photoconversion technologies in agricultural practice, it is necessary to pay increased attention to maintaining stable conditions during plant cultivation.

Deposition of fluoropolymer coating on stainless steel surface from plasma of glow discharge

The present work investigates the application of the plasma of glow discharge to deposit the fluoropolymer coatings. Two series of experiments were carried out in which the influence of pressure and current strength on surface coatings morphology during its surface treatment with glow discharge plasma was investigated. The surface morphology is investigated by a scanning electron microscope (SEM), and the water contact angle (WCA) is measured. The fact that the choice of pressure significantly affects the morphology and properties of the deposited coating is established.

THE INFLUENCE OF COMPOSITION AND TECHNOLOGICAL FACTORS ON ADHESION STRENGTH OF FLUOROPLASTICS COATINGS TO METAL SURFACES

The ways of regulating adhesion of fluoroplastic coatings to metal surfaces are analyzed. It has been established that polymer and metal modification is necessary to increase the adhesive strength and resistance of fluoroplastic coatings. The relative impact of the nature of the metal on the strength of adhesive compounds of polymer – metal is less influenced by the nature of the polymer. The strength of metal compounds is significantly affected by the activation of the metal surface by mechanical treatment (grinding etc.). Various methods of oxidation, etching, metal phosphating are recommended to increase the adhesive strength of fluoropolymer coatings. Method of investigation of adhesion and resistance to scratch damage of coatings is given. The influence of composition and temperature-time conditions of the ground layer formation of the coating on adhesive strength of metal-polymeric compounds was investigated. Detailed operation modes are described. The properties of the ground layer of fluoropolymer Ф-30П are given. The peculiarities of the fluoroplastic coating ground layer formation are outlined. The technology of application of the fluoroplastic coating ground layer on electroplating of metal surfaces has been developed. The coating on the metal surface was done by electrostatic spraying of the ground layer powder at an electric field voltage of 50 kV. The deformation and strength properties of the unstabilized Ф-30П fluoroplast are found to be quite high, which together with high adhesive strength makes it possible to recommend this polymer as primer. It is also advisable to melt the ground layers in more rigid temeperature-time modes (melting temperature 2600 C, duration – 2 hours) in order to ensure higher adhesion strength. The adhesive strength of the Ф-30П fluoroplastic coating can be increased by 10-15% by additional heating at a temperature of 2400 C for two hours. Analysis of the results showed that the resistance of fluoroplastic coatings based on Ф-30П to damage by scratching with an increase in the graphite content of C-1 from 15% to 25% increases by a factor of 2.11, and inserting to coating with 25 mas.% of C-1 graphite additional 3 mas. % of the aerosil-based amino-ergoholozenese – 3.16 times. The additional termoprocessing of these coatings increases the resistance to damage by scratching by 30 per cent. Recommendations on the use of research results for obtaining fluoroplastic coatings with high-adhesion to metal surfaces are given.

Characterization of graphene-filled fluoropolymer coatings for condensing heat exchangers.

Condensing heat exchangers are thermal devices subjected to extremely corrosive environments due to the formation of acidic condensates on the heat-exchange elements during service. To protect the heat exchangers from chemical attack, perfluoroalkoxy (PFA) coating has been applied as a barrier layer onto the surfaces of the heat-exchange elements to prevent corrosion. However, PFA has intrinsically poor thermal conductivity, and low wear resistance; thus, it is not naturally a good material for heat exchanger application. In this study, graphene nanoplatelets (GNPs) are incorporated into PFA powder as coating materials to improve the thermal properties of the fluoropolymer, for condensing heat exchangers application. Two grades of GNPs (8 nm and 60 nm layer thickness) are tested to evaluate the effect of graphene addition on the thermal, adhesion, electrical, and wear properties of the composites, which are compared to those mixed with multi-walled carbon nanotubes (MWCNTs). The results showed that both grades of GNPs significantly increased the thermal conductivity, i.e., ∼8× that of the virgin PFA. The composites incorporated with both grades of GNPs also demonstrated good coating adhesion strength and wear resistance, as well as excellent corrosion resistance. The composite filled with MWCNTs exhibited poor surface finish and minimal improvement in thermal performance.

The testing methods for anti-icing properties of ultra-thin fluoropolymer coatings

The paper discusses the testing methods of ultra thin film-forming fluorocontained polymer compositions, which form the surface modifying structures, long-life coatings and nanosize films, giving the treated surface anti-icing, tribological and hydrophobic properties.

Detection and diversity of fluorinated oil- and water-repellent coatings on apparel fibers.

Fluorinated coatings, often used for oil and water repellency and stain resistance in fabrics, are potentially persistent forensic fiber markers. However, they have received limited attention because of challenges in their detection caused by the small size of a single fiber and thin nature of stain-resistant coatings. Here, we utilize a sensitive fluorine-selective analytical technique to detect and evaluate diversity of fluorinated coatings in apparel. Twelve clothing items marketed as stain-resistant were tested with nine showing oil- and water-repellent properties. Fluorinated pyrolysis products of single fibers from all of the nine items were detected by gas chromatography coupled to plasma-assisted reaction chemical ionization mass spectrometry (GC-PARCI-MS), indicating the prevalence of fluoropolymer coatings in stain-resistant clothing articles. Furthermore, three major classes of fluorinated coatings were identified via principal component analysis of pyrogram patterns. The classes were coating-specific and did not correlate with fiber core and color, highlighting a robust detection methodology. To evaluate the effect of fiber lifting in crime scenes, fibers from the 9 clothing items were used to develop a multinomial logistic regression model based on pyrogram principal components. The model was then tested using fibers subjected to contact with Post-it® notes. The test set fibers were sampled from the clothing items of the training set and from three additional garments of differing color but the same brands as the training set. The coating classes were predicted with 98.4% accuracy, confirming robust classification of fiber coatings using py-GC-PARCI-MS regardless of fiber color, core, and fiber lifting.

Fluoropolymer coatings deposited on rotating cylindrical surfaces by HW CVD: experiment and simulation

The hot wire chemical vapor deposition method has been adapted to deposit fluoropolymer coatings on small-radius rotating surfaces. The influence of the rotational frequency of a cylindrical sample during the deposition process on the formation of a layer of fluoropolymer coating was studied. It was found that the rotational frequency of the cylindrical sample significantly changed the morphology of the resulting coating. It was shown that with an increase in the sample’s rotational frequency from 1 to 100 rpm, the deposition rate decreased and the coating structure degraded. To establish the reasons for this effect, a numerical study of the flow around a rotating cylindrical sample was carried out for a range of low gas velocities and densities in the reactor. The simulations are based on solving the Navier–Stokes equation with no slip and velocity slip boundary conditions for a rotating surface. It was found that the main reason for the decrease in the deposition rate was associated with the effect of the formation of a closed circulation flow region above the sample’s surface during rotation. The dependence of the characteristic size of this region on the rotational frequency of the cylinder sample was close to linear. The effects of surface boundary conditions were also analyzed.

Hot-Wire Chemical Vapor Deposition of Fluoropolymer Coatings on Rotating Cylindrical Surfaces

The method of hot-wire activated chemical vapor deposition (HW CVD) of fluoropolymer films has been adapted to obtain fluoropolymer coatings on rotating cylindrical surfaces of small radius (below 20 mm). The influence of the substrate rotation speed on the structure of thin fluoropolymer deposit was studied and revealed significant dependence of the coating morphology on the speed of cylindrical surface rotation, which is an additional parameter that can be used to control the structure of fluoropolymer coating during the HW CVD process.

Effect of Laser Texturing and Ti Bond Coat for Film Forming Property of Cold Sprayed Fluoropolymer Coatings

Effect of Laser Texturing and Ti Bond Coat for Film Forming Property of Cold Sprayed Fluoropolymer Coatings

Осаждение фторполимерных покрытий на вращающиеся цилиндрические поверхности методом химического осаждения из газовой фазы, активированной горячей нитью

The Hot Wire Chemical Vapor Deposition method has been adapted to deposit fluoropolymer coatings onto rotating cylindrical surfaces with a small radius (less than 20 mm). The effect of the surface rotation frequency on the structure of a thin fluoropolymer coating deposited on it has been investigated. A significant change in the morphology of the formed fluoropolymer coating was found depending on the rotational frequency of the cylindrical surface. One more parameter has been established that makes it possible to change the structure of the formed fluoropolymer coating during the deposition process.

Features of Boiling Heat Transfer at Various Pressures on Hydrophilic/Hydrophobic Surfaces

The effect of surface wettability and pressure on multiscale heat transfer characteristics at liquid boiling was studied. The experiments were carried out at saturated water boiling on surfaces with different wettability in the pressure range of 8.8–103 kPa. The usage of transparent ITO film heater deposited on a sapphire substrate and high-speed visualization showed the nucleation site density to reduce with decreasing pressure and to significantly increase on heaters with hydrophobic fluoropolymer coatings. The results on the vapor bubble growth rate, bubble emission frequency, and evolution of the triple contact line at spreading of dry spots are also analyzed in detail. In particular, the rate of dry spot growth on a hydrophilic surface was shown to have a non-monotonic dependence with the lower extremum at pressures in the range of 22–42 kPa depending on the heat flux. The usage of high-speed infrared thermography enabled measurement of the temperature field of the heating surface and determination of the heat transfer rate at boiling depending on the pressure and surface wettability. The heat transfer was shown to decrease with the pressure at boiling on hydrophilic heaters, whereas it can be significantly enhanced due to a hydrophobic coating at atmospheric pressure in the range of low heat fluxes.