Improved adhesion of poly(tetrafluoroethylene) by NH3-plasma treatment

—Surface modification of poly(tetrafluor oethylene) (PTFE) by NH₃-plasma treatment was investigated by means of contact angle measurement, XPS, and ATR FT/IR spectroscopy. The modified surfaces were adhesively bonded to nitril rubber. The NH₃-plasma irradiation made PTFE surfaces hydrophilic. The contact angle of water on the modified PTFE surface was 16 deg, and the surface energy was 62-63 mJ/m². The NH₃-plasma irradiation improved adhesion between PTFE and nitril rubber using a phenol-type adhesive. The peel strength of the joints reached 8.1 × 10³ N/m. Carbonyl and amido groups were created on PTFE surfaces by the NH₃-plasma irradiation. The mechanism of the improvement of adhesion by the NH₃-plasma irradiation is discussed.     

Modification of emission properties of diamond films due to surface treatment process

The modification on the characteristics of the chemical vapor deposited (CVD) diamond films due to H₂-plasma post-treatment, SiO₂-coating and Cr-coating has been examined. A negatively biased H₂-plasma post-treatment process leads to pronounced modification on the morphology, Raman spectroscopy and electron field emission properties of the diamond films, whereas a positively biased H₂-plasma post-treatment process changes these characteristics insignificantly. The emission current density of the diamond films increased markedly to 162.1 μA cm⁻² due to negatively biased H₂-plasma etching, which is presumably caused by the formation of nano-sized columnar grains resulted from the etching of diamonds. On the other hand, the electron field emission capacity of the diamond films was completely suppressed due to the coating and chemical etching of SiO₂ layer, which is ascribed to the formation of a silicon-oxy-carbon (Si_1-x-yC_xO_2y) layer. Only when the SiO₂ layer is subjected to a negatively biased (−50 V) H₂-plasma etching process, can the electron field emission capacity of the diamond films be fully recovered. In contrast, emission current density (J_e) was increased substantially to 642 μA cm⁻² and the turn-on field (E₀) was lowered from 10.2 to 5.8 V μm⁻¹ due to Cr-coating. Scanning electron microscopic (SEM) and Auger electron spectroscopic (AES) examinations reveal that the main factor improving these behaviors for the Cr-coated diamond films is the formation of diamond-like carbon films on their top surface.     

Surface modification of Kevlar 149 fibers by gas plasma treatment

Kevlar 149 fibers have been surface treated with NH₃-, 0₂-, or H₂O-plasm to modify the fiber surfaces. SEM (scanning electron microscopy) is used to characterize the surface topography of fibers etched by gas plasmas. The chemical compositions and functional groups of the fiber surfaces are identified by ESCA (electron spectroscopy for chemical analysis) and SSIMS (static secondary ion mass spectroscopy), respectively. The contact angle of water on modified PPTA [poly(p-phenylene terepbthalamide)] film prepared from using Kevlar 149 fibers is also used to investigate the wettability. The results show that the etching abilities of gas plasmas are dependent on the type of gas used for plasma treatments. The contact angle data indicate that all the three gas plasma treatments are effective in rendering the surface of PPTA more hydrophilic. The ESCA analysis results show that the surface compositions of plasma-treated fibers are highly dependent on the type of gas used and treatment time. Changes in surface compositions of fibers treated by NH₃-, O₂-, and H₂O-plasma are observed. Increasing nitrogen and oxygen contents are observed for the NH₃-plasma treatment, and the O₂- and H₂O-plasma treatments, respectively. Furthermore, the incorporation of amino groups into fiber surfaces by NH₃-plasma treatment and the extensive damage of the aromatic ring and the polymer backbone by H₂O-plasma and O₂-piasma are evidenced by SSIMS.     

Relationship between the passivation of TiO2 particles and LLDPE photodegradation: a comparison between bulk and surface impacts

The effect of the concentration of alumina (Al₂O₃) and silica (SiO₂) used to passivate titanium dioxide (TiO₂) particles on the photodegradation of plastic films containing these particles was investigated. The films were made of linear low-density polyethylene (LLDPE) containing four different types of passivated TiO₂ particles. The UV degradation of the films was evaluated for the surface and the bulk by measuring the physical and chemical changes as a function of time. The surface chemical and physical degradation effects were measured by ATR-FTIR and AFM, respectively. A statistical Gaussian adjustment was proposed to correlate the AFM depth profiles of the eroded surfaces of the films after the photodegradation process. The bulk physical effect was evidenced by the loss of mechanical properties in the films. The results showed that the higher the concentrations of Al₂O₃ are, the better the inhibition of the photodegradation of the LLDPE films. In this study, it was confirmed that the observed UV degradation effect correlated at both the surface and bulk levels. The results showed not only the reduction of the photodegradative effect as the passivation of the TiO₂ particles increased but also the possibility of using these particles as UV stabilizers of LLDPE films. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47026.     

Variations in Reactivity on Different Crystallographic Orientations of Cerium Oxide

Cerium oxide is a principal component in many heterogeneous catalytic processes. One of its key characteristics is the ability to provide or remove oxygen in chemical reactions. The different crystallographic faces of ceria present significantly different surface structures and compositions that may alter the catalytic reactivity. The structure and composition determine the number of coordination vacancies surrounding surface atoms, the availability of adsorption sites, the spacing between adsorption sites and the ability to remove O from the surface. To investigate the role of surface orientation on reactivity, CeO₂ films were grown with two different orientations. CeO₂(100) films were grown ex situ by pulsed laser deposition on Nb-doped SrTiO₃(100). CeO₂(111) films were grown in situ by thermal deposition of Ce metal onto Ru(0001) in an oxygen atmosphere. The chemical reactivity was characterized by the adsorption and decomposition of various molecules such as alcohols, aldehydes and organic acids. In general the CeO₂(100) surface was found to be more active, i.e. molecules adsorbed more readily and reacted to form new products, especially on a fully oxidized substrate. However the CeO₂(100) surface was less selective with a greater propensity to produce CO, CO₂ and water as products. The differences in chemical reactivity are discussed in light of possible structural terminations of the two surfaces. Recently nanocubes and nano-octahedra have been synthesized that display CeO₂(100) and CeO₂(111) faces, respectively. These nanoparticles enable us to correlate reactions on high surface area model catalysts at atmospheric pressure with model single crystal films in a UHV environment.     

Effect of H2S on the CO2 corrosion of carbon steel in acidic solutions

The objective of this study is to evaluate the effect of low-level hydrogen sulfide (H₂S) on carbon dioxide (CO₂) corrosion of carbon steel in acidic solutions, and to investigate the mechanism of iron sulfide scale formation in CO₂/H₂S environments. Corrosion tests were conducted using 1018 carbon steel in 1 wt.% NaCl solution (25 °C) at pH of 3 and 4, and under atmospheric pressure. The test solution was saturated with flowing gases that change with increasing time from CO₂ (stage 1) to CO₂/100 ppm H₂S (stage 2) and back to CO₂ (stage 3). Corrosion rate and behavior were investigated using linear polarization resistance (LPR) technique. Electrochemical impedance spectroscopy (EIS) and potentiodynamic tests were performed at the end of each stage. The morphology and compositions of surface corrosion products were analyzed using scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The results showed that the addition of 100 ppm H₂S to CO₂ induced rapid reduction in the corrosion rate at both pHs 3 and 4. This H₂S inhibition effect is attributed to the formation of thin FeS film (tarnish) on the steel surface that suppressed the anodic dissolution reaction. The study results suggested that the precipitation of iron sulfide as well as iron carbonate film is possible in the acidic solutions due to the local supersaturation in regions immediately above the steel surface, and these films provide corrosion protection in the acidic solutions.     

Surface degradation and hydrophobic recovery of polyolefins treated by air corona and nitrogen atmospheric pressure glow discharge

The surface degradation and production of low molecular weight oxidized materials (LMWOM) on biaxially oriented polypropylene (BOPP) and low‐density polyethylene (LDPE) films was investigated and compared for two different dielectric barrier discharge (DBD) treatment types, namely air corona and nitrogen atmospheric pressure glow discharge (N₂ APGD). Contact angle measurements, X‐ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) analyses were performed in conjunction with rinsing the treated films in water. It is shown that N₂ APGD treatments of both polyolefins result in much less surface degradation, therefore, allowing for a significantly higher degree of functionalization and better wettability. Hydrophobic recovery of the treated films has also been studied by monitoring their surface energy (γ_s) over a period of time extending up to several months after treatment. Following both surface modification techniques, the treated polyolefin films were both found to undergo hydrophobic recovery; however, for N₂ APGD modified surfaces, γ_s ceases to decrease after a few days and attains a higher stable value than in the case of air corona treated films. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1291–1303, 2004     

Ultrathin DLC and SiOx layer deposition on poly(ethylene terephthalate) and restriction of surface dynamics

The hydrophilicity of oxygen plasma‐reated polymer surfaces decays with storing time in air environments. Because they are dense, highly crosslinked, and chemically stable, diamond‐like carbon (DLC) films and silicon oxide films (SiO_x) were deposited on poly(ethylene terephthalate) by plasma‐enhanced chemical vapor deposition to restrict polymer surface dynamics. In this study, the effects of ultrathin films on surface dynamics of these polymers were investigated. The layers were deposited on substrates with thickness below 100 Å. The thickness of films was measured with a scanning analyzer ellipsometer, while ATR‐IR spectroscopy and Raman spectroscopy were performed to observe the chemical structure of the films. Films below 50 Å were also shown to be effective in stabilizing the plasma treated polymer surfaces. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1158–1164, 2000     

Nylon surface modification. Part 1. Targeting the amide groups for selective introduction of reactive functionalities

Nylon is a widely used synthetic polymer because it has a combination of strength, flexibility, toughness, and abrasion resistance. For a variety of applications, however, it is necessary to impart desired surface properties by introducing specific functional groups in specific locations and densities. Several chemical modification methods were developed for the introduction of functional groups to nylon surfaces using amide-selective reactions without cleaving the polymer chains. Activation of amides by reaction with potassium tert-butoxide (t-BuOK) facilitates the N-alkylation of surface amides. When 2-bromoethylamine hydrobromide (BEA-HBr) was employed as an alkylating agent, surfaces with a mixture of primary/secondary/tertiary amine groups were obtained. Alkylation with (3-glycidoxypropyl)triethoxysilane (GPTES) was utilized to prepare surfaces with silica-like reactivity. Chemical reduction with borane-THF complex (BH₃-THF) results in a 69% conversion of surface amide groups to the corresponding secondary amines. A kinetic study of this reaction for different types of nylon films revealed that the yield was dependent on the segmental mobility of the polymer. These surfaces are useful substrates for the fabrication of nylon-supported composite films.     

Surface properties of polymers treated with tetrafluoromethane plasma

Polymer films of poly(ethylene terephthalate), polypropylene, and cellophane were surface treated with tetrafluoromethane plasma under different time, power, and pressure conditions. Contact angles for water and methylene iodide and surface energy were analyzed with a dynamic contact angle analyzer. The stability of the treated surfaces was investigated by washing them with water or acetone, followed by contact angle measurements. The plasma treatments decreased the surface energies to 2–20 mJ/m² and consequently enhanced the hydrophobicity and oleophobicity of the materials. The treated surfaces were only moderately affected after washing with water and acetone, indicating stable surface treatments. The chemical composition of the material surfaces was analyzed with X-ray photoelectron spectroscopy (XPS) and revealed the incorporation of about 35–60 atomic % fluorine atoms in the surfaces after the treatments. The relative chemical composition of the C ls spectra's showed the incorporation of —CHF— groups and highly nonpolar —CF₂— and —CF₃ groups in the surfaces and also —CH₂—CF₂— groups in the surface of polypropylene. The hydrophobicity and oleophobicity improved with increased content of nonpolar —CF₂—, —CF₃, and —CH₂—CF₂— groups in the surfaces. For polyester and polypropylene, all major changes in chemical composition, advancing contact angle, and surface energy are attained after plasma treatment for one minute, while longer treatment time is required for cellophane. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1591–1601, 1997     

Mechanism of gas transport in plasma treated glassy polymer films

The effect of oxygen- and Ar-plasma treatment on glassy polysulfone and polyimide films upon the gas diffusion process was investigated in the permeation of CO₂ and H₂. The plasma treatment apparently induced a reduction of only the diffusivity of Henry's law population, while the diffusion coefficient of the Langmuir population was not altered by plasma treatment. The oxygen- and Ar-plasma treatment on polysulfone films is favorable for permselectivity of H₂ relative to CO₂. Such a surface modification of polyimide films appears to be ineffective for improvement of permselectivity of H₂.     

Effect of using oxygen,carbon dioxide,and carbon monoxide as active gases in the atmospheric plasma treatment of fiber-reinforced polycyanurate composites

A study was undertaken to address the effect of using different active gases during the atmospheric plasma treatment of composite specimens for adhesive bonding. The effect of using oxygen, carbon dioxide, or carbon monoxide on the surface chemistry, morphology, and mechanical properties of cyanate ester composites was investigated. CO treatment resulted in a surface profile that could be tailored to create an oxygen/carbon ratio as high as 0.71 with a negligible degree of polymer degradation as verified by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy. On the other hand, CO₂ and O₂ treatments resulted in a fairly high degree of chain scission and degradation using otherwise similar treatment conditions. However, significant bond strength improvement (>75%) over conventional abrasion surface preparation techniques was achieved for all three types of gases. XPS of CO-treated specimens showed a large increase in carbonyl species formation in comparison with the weakly bonded carbonates (ash) formed when treating the same composites with CO₂ and O₂ gas suggesting a different mechanism. These results present a method by which sensitive carbon-based, hydrophobic surfaces can be modified without damaging the underlying substrate as well as improving bond performance over conventional surface preparation methods. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Enhanced photocatalytic activity of highly transparent superhydrophilic doped TiO2 thin films for improving the self-cleaning property of solar panel covers

Undoped and metal doped nanocrystalline TiO₂ transparent thin films were synthesized on glass substrates via sol-gel/dip-coating method. TiO₂ thin film coatings can be applied to the surfaces of solar panels to impart self-cleaning properties to them. The structural and optical properties of few nanometer-thick films were characterized by XRD, SEM, CA, AFM, XPS, and UV–Vis spectrophotometry techniques. The stoichiometric TiO₂ films crystallized in anatase phase, with a particle size of ～100 nm, which were uniformly distributed on the surface. The prepared films with a roughness of ～1–5 nm, increased the hydrophilicity of the glass surface. Reducing the amount of Ti precursor (X) favored the improvement of film quality. To improve the photocatalytic activity of the TiO₂ thin film, it was doped with Ni, Cd, Mo, Bi and Sr metal ions. The effect of metal doping on the photocatalytic activity of the films was investigated using the degradation process of methylene blue (MB) dye as the model contaminant. Among the prepared coatings, the Sr–TiO₂ film showed the highest efficiency for MB degradation. It increased the dye degradation efficiency of the films under both UV and Vis lights. The kinetic investigations also showed that the degradation of MB by TiO₂ and M ? TiO₂ films obeyed the pseudo-first order kinetics.     

Improvement of CO2 adsorption on ZIF-8 crystals modified by enhancing basicity of surface

The imidazolate framework ZIF-8 samples were modified separately by using ammonia impregnation and thermal treatment in atmosphere of N₂ or H₂ in order to improve its adsorption property toward CO₂, and the modified samples A-ZIF-8, N-ZIF-8 and H-ZIF-8 were correspondingly available. The modified ZIF-8 samples were characterized, and the surface chemical properties of the ZIF-8 samples were determined separately by FTIR, CO₂-TPD, NH₃-TPD and H₂O-TPD. The isotherms of CO₂ on the modified ZIF-8 samples were measured. Results showed that after surface modification, the total amounts of basicity of the modified samples significantly increased, and followed the order: A-ZIF-8>H-ZIF-8>N-ZIF-8>O-ZIF-8. The uptakes of CO₂ increased proportionally with the basic groups on the surfaces of the ZIF-8 samples due to CO₂ being an acidic molecule. As a consequence of that, the CO₂ adsorption capacity of the samples followed the order: A-ZIF-8>H-ZIF-8>N-ZIF-8>O-ZIF-8. The amount adsorbed of CO₂ on the modified ZIF-8 sample by ammonia impregnation is the highest, having an increase.     

Plasma assisted immobilization of poly(ethylene oxide) onto fluorocarbon surfaces

Different plasma-assisted procedures were compared with respect to the immobilization of poly(ethylene oxide) (PEO) and poly(ethylene-block-propylene) triblock copolymers (PEO-PPO-PEO) on top of thin plasma-deposited fluorocarbon layers. The fluorocarbon substrate was used as a model system for the common poly(tetrafluoroethylene) as it provides several advantages to apply surface-selective analytical methods. The fixation of pre-adsorbed PEO-PPO-PEO by argon plasma treatments on the fluorocarbon surface was found to produce less homogeneous coatings probably due to the insufficient adsorption of the triblock-copolymers on the substrate. More effective PEO coverage of the fluorocarbon surface was achieved by O₂-plasma initiated graft polymerization of PEO-dimethacrylate (M_w = 400 g/mol) and PEO-monoacrylate (M_w = 1000 g/mol) from solutions or melts. X-ray photoelectron spectroscopy (XPS) and contact angle measurements were utilized for a detailed study of the modified surfaces. The efficiency of PEO-coatings with respect to the reduction of protein adsorption onto the hydrophobic fluorocarbon layer was demonstrated with the example of the adsorption of fibrinogen. The adsorbed amount of this protein was determined based on spectroscopic ellipsometry.     

Influence of hole-scavenger and different withdrawn speeds on photocatalytic activity of Co3O4 thin films under sunlight irradiation

Cobalt oxide (Co₃O₄) thin films with environmentally friendly properties and high photocatalytic activity under sunlight were employed in this work as a beneficial and cost-effective material. This research provides a novel study for cobalt oxide (Co₃O₄) thin films that were dip-coated on pretreated glass substrates at different withdrawn speeds. The structure, surface morphology, surface roughness, and optical properties were studied and discussed. The photocatalytic performance of cobalt oxide thin films was investigated via degradation of blue methylene (BM) under sunlight irradiation. In addition, the effect of hole-scavengers on the feed of conduction band by electrons was investigated. 5 mm/s withdrawn speed achieved high photocatalytic efficiency at 78% correspond to (220) growth orientation, 39.7 nm of crystal size, 2.01 eV of band gap energy, and 55 nm surface roughness. At the same withdrawn speed, BM degradation was improved by 9.47, 17.57, and 20.09% for Co₃O₄ thin films with the presence of hole-scavengers Octan-1-ol, EDTA, and H₂O₂, respectively. All the films show hydrophilic surface properties as the contact angle was under 60°. Emphasized the potential for application to various types of organic contaminants from various wastewater sources under sunlight irradiations.     

Surface modification of nanocrystalline diamond/amorphous carbon composite films

The surfaces of nanocrystalline diamond/amorphous carbon (NCD/a-C) nanocomposite films deposited from a 17% CH₄/N₂ mixture have been subjected to a variety of plasma and chemical treatments, namely H₂ and O₂ microwave plasmas, a CHF₃ 13.56 MHz plasma, and a chemical treatment with aqua regia (HCl:HNO₃ 3:1). The resulting surfaces have been studied with respect to their chemical nature by X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (TOF-SIMS), concerning their morphology with atomic force microscopy, and by contact angle measurements to study their hydrophobicity and their stability. As-grown surfaces are hydrogen terminated, but the number of C–H bonds can slightly be increased by a H₂ microwave plasma, while treatment with aqua regia considerably lowers the number of C–H bonds at the surface. O₂ and CHF₃ plasmas, on the other hand, lead to a replacement of the terminating C–H bonds by C–O or C–OH and C–F_x groups, respectively. Finally, by contact angle measurements over a period of 150 days it could be shown that the H-terminated surface is very stable whereas the contact angle of the O-treated surface changed considerably with time, probably due to the adsorption of contaminants.     

Thermal desorption study of the acetic acid decomposition on clean Ni/Cu(110) alloy surfaces

The decomposition of acetic acid was studied on a clean Ni/Cu(110) alloy single crystal by means of thermal desorption spectroscopy. The primary alloy surface composition employed in this work was 37% Ni and 63% Cu as measured by Auger electron spectroscopy. Acetate was the predominant surface intermediate observed, giving rise to the CO₂ and H₂ decomposition products observed, in analogous fashion to the decomposition of formic acid. Surface carbon residue was also detected and could be driven into the bulk by annealing the sample above 900 °K. The rate constant for the decomposition of the acetate intermediate on the alloy was found to be 10^13.5 exp(?33(kcal/mol)/RT)sec^?1. The autocatalytic decomposition of both carboxylic acids previously observed on a clean Ni(110) surface was totally suppressed. The product distribution from acetic acid observed on both the 37% Ni/65% Cu alloy and the carburized Ni(110) surfaces were very similar, indicating chemical similarities between these two surfaces. At high coverages of the acetate intermediate the activation energy for CO₂ formation increased by 14 kcal/gmol. This effect was attributed to strong attractive interactions in the adsorbate layer.     

Adhesion of SiO2 thin films to plasma-treated SUS304 stainless steel substrates

The adhesion strength of the coated SiO₂ thin film to SUS304 stainless steel substrates with various surface treatment conditions is studied in this research. The surface of the SUS304 stainless steel substrate is first treated with 1000-W plasma and then a SiO₂ thin film is deposited onto the surface via radio-frequency magnetron sputtering. Scanning electron microscopy is employed to observe the surface and cross section of the coating and X-ray diffraction is used to analyze the crystallographic structure. Moreover, a nanoscratch test instrument was employed to examine the indentation, scratches, coating hardness, modulus of elasticity, coefficient of friction, and critical adhesion of the SiO₂ film and to obtain surface profiles. A comparison of the coating adhesion of the substrate surfaces with and without plasma treatment indicates that critical adhesion increases significantly after Ar/N₂/O₂ plasma treatment.     

Study of nisin adsorption on plasma-treated polymer surfaces for setting up materials with antibacterial properties

Setting up antibacterial materials by nisin adsorption on surfaces depends mainly on the surface properties and the surface treatments allowing the modification of such properties. In order to investigate the factors affecting such adsorption, the native low density polyethylene (LDPE) was modified using Argon/Oxygen (Ar/O₂) plasma, nitrogen (N₂) plasma and plasma-induced grafting of acrylic acid (AA). The films were studied by various characterization techniques. The chemical surface modification was confirmed by X-ray photoelectron spectroscopy (XPS), the wettability of the surfaces was evaluated by contact angle measurements, the surface charge was determined by the zeta potential measurements, and the changes in surface topography and roughness were revealed by atomic force microscopy (AFM). Nisin was adsorbed on the native and the modified surfaces. The antibacterial activity, the nisin adsorbed amount, and the peptide distribution were compared for the four nisin-functionalized films. The highest antibacterial activity was recorded on the Ar/O₂ followed by AA then by N₂ treated films and the lowest activity was on the native film. The observed antibacterial activity was correlated to the type of the surface, hydrophobic and hydrophilic interactions, surface charge, surface topography, nisin adsorbed amount, and nisin distribution on the surfaces.