Formation of functional groups on graphite during oxygen plasma treatment

Improved sample wettability was obtained by oxygen plasma functionalization of pyrolytic graphite. The samples were exposed to highly dissociated oxygen plasma with the density of 1 × 10¹⁶ m⁻³, the electron temperature of about 5.5 eV and the density of neutral oxygen atoms of 8 × 10²¹ m⁻³ for 20 s. The surface wettability was measured by a contact angle of water drop. The contact angle dropped from original 112° down to about 1°. The functional groups were detected by XPS analyses. The survey spectrum showed a substantial increase of oxygen concentration on the surface, while high-resolution analyses showed additional oxygen was bonded onto the graphite surface in the form of C-O polar functional group responsible for the increase of the surface energy.     

Wetting and superhydrophobic properties of PECVD grown hydrocarbon and fluorinated-hydrocarbon coatings

Wetting characteristics of micro-nanorough substrates of aluminum and smooth silicon substrates have been studied and compared by depositing hydrocarbon and fluorinated-hydrocarbon coatings via plasma enhanced chemical vapor deposition (PECVD) technique using a mixture of Ar, CH₄ and C₂F₆ gases. The water contact angles on the hydrocarbon and fluorinated-hydrocarbon coatings deposited on silicon substrates were found to be 72° and 105°, respectively. However, the micro-nanorough aluminum substrates demonstrated superhydrophobic properties upon coatings with fluorinated-hydrocarbon providing a water contact angle of ∼165° and contact angle hysteresis below 2° with water drops rolling off from those surfaces while the same substrates showed contact angle of 135° with water drops sticking on those surfaces. The superhydrophobic properties is due to the high fluorine content in the fluorinated-hydrocarbon coatings of ∼36 at.%, as investigated by X-ray photoelectron spectroscopy (XPS), by lowering the surface energy of the micro-nanorough aluminum substrates.     

Fabrication of a superhydrophobic ZnO nanorod array film on cotton fabrics via a wet chemical route and hydrophobic modification

A superhydrophobic ZnO nanorod array film on cotton substrate was fabricated via a wet chemical route and subsequent modification with a layer of n-dodecyltrimethoxysilane (DTMS). The as-obtained cotton sample was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), scanning probe microscope (SPM) and X-ray photoelectron spectroscopy (XPS), respectively. The wettability of the cotton fabric sample was also studied by contact angle measurements. The modified cotton fabrics exhibited superhydrophobicity with a contact angle of 161° for 8 μL water droplet and a roll-off angle of 9° for 40 μL water droplet. It was shown that the proper surface roughness and the lower surface energy both played important roles in creating the superhydrophobic surface, in which the Cassie state dominated.     

Biological response of stainless steel surface modified by N2O/O2 glow discharge plasma

Stainless steel wafers were treated with the glow discharge plasma of mixed N₂O and O₂ at different molar ratios at a certain discharge condition to create desirable biological characteristics to the surfaces. It was found that the molar ratio of N₂O to O₂ in the mixture at 1:1 used for plasma surface modification caused high apoptotic percentage. Contact angle measurement showed that the surface of stainless steel samples became very hydrophilic after the plasma modification with a value of 15°-30°. The control stainless steel chips without plasma treatment had a contact angle of 40 ± 2°. The data of Electron Spectroscopy for Chemical Analysis (ESCA) indicated that there was a certain amount of oxynitrites formed on the plasma treated surfaces, which was considered to play an important role to cell apoptosis and anti-clot formation in cell culture tests. The ESCA depth profile of up to 250 Å from the top surface showed the change of elemental compositions within 40-50 Å of the surface by the plasma treatment. The decreased platelet attachment, combined with increased apoptosis in fibroblasts is a distinct combination of biological responses arising from the mixed gas plasma treatment. These initial results suggest it may be of particular use relative to stainless steel stents where decreased platelet attachments are advantageous and induction of apoptosis could limit in-stent restenosis.     

Weathering properties of treated southern yellow pine wood examined by X-ray photoelectron spectroscopy, scanning electron microscopy and physical characterization

In this study the weathering behavior of southern yellow pine (SYP) wood samples pretreated in different solutions has been examined using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and various types of physical characterization regarding material loss and discoloration. The treatment solutions include water as a control, a commercially available water repellent (WR) wood treating additive and polyethylene glycol (PEG) products including PEG PLUS™, PEG 8000 solutions and Compound 20M in varying concentrations. All contained the wood preservative chromated copper arsenate (CCA). One sample was treated with a CCA solution only. The treatments were carried out at 20 °C and 150 psig for 1/2 h after exposure to vacuum (28 mmHg) for 15 min. Simulated weathering was achieved in an Atlas 65-W Weather-Ometer for 2000 h with both light and dark periods and rain. The temperature ranged from 23 °C during the dark cycle to 35 °C during the light cycle. With weathering the XPS O/C ratios increase due to oxidation of the surface. Exposure to UV light results in bond breakage and reaction with oxygen in the presence of air to form organic functional groups such as , , CO and/or O-C-O. These oxidized products can protect the underlying wood from deterioration if they are insoluble in water and remain on the surface as a protective coating. If soluble, rain washes the compounds away and assists in the degradation. Correlated changes are observed in the XPS O/C ratios, the high-resolution XPS C 1s spectra, the SEM micrographs and physical measurements including thickness alteration, weight loss, and discoloration by yellowing or whitening of the weathered wood. The PEG treatments are effective in protecting wood with the 2% PEG PLUS treatment providing the best weathering behavior similar to that of the CCA treatment. The WR and water treatments yield the poorest weathering properties.     

Effect of H2 and O2 plasma etching treatment on the surface of diamond-like carbon thin film

In this study, we investigated the surface properties of diamond-like carbon (DLC) films for biomedical applications through plasma etching treatment using oxygen (O₂) and hydrogen (H₂) gas. The synthesis and post-plasma etching treatment of DLC films were carried out by 13.56 MHz RF plasma enhanced chemical vapor deposition (PECVD) system. In order to characterize the surface of DLC films, they were etched to a thickness of approximately 100 nm and were compared with an as-deposited DLC film. We obtained the optimum condition through power variation, at which the etching rate by H₂ and O₂ was 30 and 80 nm/min, respectively. The structural and chemical properties of these thin films after the plasma etching treatment were evaluated by Raman and Fourier transform infrared (FT-IR) spectroscopy. In the case of as-deposited and H₂ plasma etching-treated DLC film, the contact angle was 86.4° and 83.7°, respectively, whereas it was reduced to 35.5° in the etching-treated DLC film in O₂ plasma. The surface roughness of plasma etching-treated DLC with H₂ or O₂ was maintained smooth at 0.1 nm. These results indicated that the surface of the etching-treated DLC film in O₂ plasma was hydrophilic as well as smooth.     

Role of reactive gas in atmospheric plasma for cell attachment and proliferation on biocompatible poly ?-caprolactone film

This paper reports the surface modification of a biocompatible poly ?-caprolactone (PCL) film treated by atmospheric cold plasma (ACP) with reactive gases. The change in wettability and surface morphology of the PCL film after the plasma treatment with the reactive gases (Ar, H₂, N₂ and O₂) were determined using contact angle and surface roughness measurements. The chemical bonding states and molecular vibration modes of the activated organic groups on the polymer surface were examined by X-ray photoelectron spectroscopy and Fourier-transformation infrared techniques. The surface of the ACP-treated PCL films was also examined for their in vitro cell attachment and proliferation using human prostate epithelial cells (HPECs). The increase in the hydrophobicity of the Ar + H₂ plasma-treated PCL film resulted in a lower cell loading in the initial step of cell culture as well as a decrease in the level of cell attachment and proliferation compared with the pristine film. However, the hydrophilic properties of the Ar + N₂, Ar and Ar + O₂ plasma-treated PCL film improved the adhesion properties. Therefore, the Ar + N₂, Ar and Ar + O₂ plasma-treated PCL films showed a better cell distribution and growth than that of the pristine PCL film. The ACP-treated PCL film is potentially useful as a suitable scaffold in biophysics and bio-medical engineering applications.     

Surface analysis of long-distance oxygen plasma sterilized PTFE film

The influence of long-distance oxygen plasma sterilization on surface properties of substrate material, i.e., medical poly(tetrafluoroethylene) (PTFE), and aging effect of these sterilized PTFE film surfaces were investigated by contact angle measurement, mass loss determination, scanning electron microscopy (SEM) as well as bacterial adhesion and platelet adhesion measurements in vitro, respectively. The changes in chemical structure of sterilized PTFE film were followed using X-ray photoelectron spectroscopy (XPS). As a result of plasma sterilization oxygen-containing functional groups (such as CO and CO), especially the CO group are introduced into PTFE surfaces, and thus pronounced increases of surface free energy and surface wettability are presented when the sample positions are within 0-40 cm. The film surface wettability degrades little as the aging time continued as long as 190 days. At the same time, the minimal surface degradation and damage occur on the sterilized PTFE when the sample position is at 40 cm. Moreover, the antibacterial adhesion and blood compatibility of sterilized PTFE surface are enhanced and the optimal effects are also obtained at 40 cm. The essential reason may be due to the optimal equilibrium between surface wettability and surface damage, which is achieved at 40 cm. Overall, of the surface properties of long-distance oxygen plasma sterilized PTFE analyzed, the sterilization at 40 cm is optimal.     

Surface chemistry of atmospheric plasma modified polycarbonate substrates

Surface of polycarbonate substrates were activated by atmospheric plasma torch using different gas pressure, distance from the substrates, velocity of the torch and number of treatments. The modifications were analyzed by contact angle measurements, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and UV-vis spectrophotometry. Plasma treatment caused the surface characteristics to become more hydrophilic as measured by the water contact angle, which decreased from 88° to 18°. The decrease in contact angle was mainly due to oxidation of the surface groups, leading to formation of polar groups with hydrophilic property. XPS results showed an increase in the intensity of -(C-O)- groups and also introduction of new functional groups i.e. -(O-CO)- after the treatment process. AFM topographic images demonstrated an increase in the rms roughness of the surface from 2.0 nm to 4.0 nm caused by the treatment. Increase in rms roughness of the surface caused relevant decrease in transmission up to ∼2-5%.     

Pre-treatments applied to oxidized aluminum surfaces to modify the interfacial bonding with bis-1,2-(triethoxysilyl)ethane (BTSE): Part I. High-purity Al with native oxide

A remote microwave-generated H₂ plasma and heating to 250 °C were separately used to modify high-purity oxidized aluminum surfaces and to assess whether these treatments can help enhance adhesion with bis-1,2-(triethoxysilyl)ethane (BTSE) coatings. Different initial oxide surfaces were considered, corresponding to the native oxide and to surfaces formed by the Forest Products Laboratory (FPL) treatment applied for either 15 or 60 min. BTSE is applied from solution at pH 4, and competing processes of etching, protonation (to form OH groups) and coupling (to form AlOSi interfacial bonds) occur at the solid-liquid interface. Scanning electron microscopy (SEM) was used to determine how the topographies of the modified Al surfaces changed with the different pre-treatments and with exposure to a buffer solution of pH 4. Secondary-ion mass spectrometry (SIMS) was used to determine the direct amount of AlOSi interfacial bonds by measuring the ratio of peak intensities 71-70 amu, while X-ray photoelectron spectroscopy (XPS) was used to determine the overall strength of the silane coating adhesion by measuring the Si 2p signals before and after application of an ultrasonic rinse to the coated sample. Measured Al 2p and O 1s spectra helped assess how the different pre-treatments modified the various Al oxidized surfaces prior to BTSE coating. Pre-treated samples that showed increased AlOSi bonding after BTSE coating corresponded to surfaces, which did not show evidence of significant etching after exposure to a pH 4 environment. This suggests that such surfaces are more receptive to the coupling reaction during exposure to the BTSE coating solution. These surfaces include all H₂ plasma-treated samples, the heated native oxide and the sample that only received the 15 min FPL treatment. In contrast, other surfaces that show evidence of etching in pH 4 environments are samples that received lower amounts of AlOSi interfacial bonding. Overall, heating improved the BTSE adhesive bonding for the native Al oxide, while H₂ plasma treatment improved the BTSE bonding for surfaces that had initially been FPL-treated for 15 and 60 min.     

Surface modification of the nanoparticles by an atmospheric room-temperature plasma fluidized bed

Using hexamethyldisiloxane (HMDSO) monomer, the magnetic nanoparticles (NPs) of nickel oxide (NiO) were modified by using an atmospheric room-temperature plasma fluidized bed (ARPFB). The plasma gas temperature of the ARPFB was not higher than 325 K, which was favorable for organic polymerization. The plasma optical emission spectrum (OES) of the gas mixture consisting of argon (Ar) and HMDSO was recorded by a UV-visible monochromator. The as-treated NPs were characterized by means of scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results show that the assembling NPs were isolated greatly after modified by the organosilicon polymer. Moreover, this treatment process changed the wettability of the NPs from super-hydrophilicity to super-hydrophobicity, and the contact angle (CA) of water on the modified NPs surface exceeded 150°. Therefore, the ARPFB is a prospective technology for the NPs surface modification according to the different requirements.     

CF4 radio frequency plasma surface modification of silicone rubber for use as outdoor insulations

For further prolonging the serve life of silicone rubber (SIR) for outdoor insulation and increasing its resistance of pollution flashover, surface modifications of SIR were carried out via CF₄ capacitively coupled plasma at radio frequency (RF) power of 60, 100 and 200 W for a treatment time up to 20 min under CF₄ flow rate of 20 sccm. Static contact angle measurement was employed to estimate the change of hydrophobicity of the modified SIR. The variation of the surface functional groups of the modified SIR was observed by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectrum and X-ray photoelectron spectroscopy (XPS). The surface topography was observed by atom force microscopy (AFM). The results indicate that the static contact angle of SIR surface is improved from 100.7° to 150.2° via the CF₄ plasma modification, and the super-hydrophobic surface of modified SIR, which corresponds to a static contact angle of 150.2°, appears at RF power of 200 W for a 5-min treatment time. According to the results, it is suggested that the formation of super-hydrophobic surface is ascribed to the co-action of the increase of roughness created by the ablation reaction of CF₄ plasma and the formation of [SiF_x(CH₃)_2−xO]_n (x = 1, 2) structure produced by the direct attachment of F atoms to Si.     

Effect of surface fluorination on the photocatalytic and photo-induced hydrophilic properties of porous TiO2 films

Porous surface-fluorinated TiO₂ (F-TiO₂) films were prepared through PEG modified sol-gel method and surface fluorination. The as-prepared films were characterized with XRD, FTIR, AFM, XPS and UV-vis DRS. The effects of surface fluorination on the photocatalytic activity and hydrophilicity of porous TiO₂ film were studied by photocatalytic degradation of rhodamine B (RhB) as well as water contact angle (CA) on porous TiO₂ film. The results showed that the surface fluorination increased the adsorption of RhB on the porous TiO₂ film and enhanced the photocatalytic degradation of RhB. The concentration and pH of NaF solutions affected much the photocatalytic activity of porous TiO₂ film. Porous F-TiO₂ film prepared in 40 mM NaF solution at pH 4.0 showed the highest photocatalytic activity. Because of its porous structure, the porous F-TiO₂ film had original water CA of 22.7°, which is much smaller than that of normal F-TiO₂ film. Under UV light irradiation, the water CA of porous F-TiO₂ film decreased to 5.1° in 90 min.     

On the synthesis and optical absorption studies of nano-size magnesium oxide powder

Magnesium oxide (MgO) nano-size powder is synthesized using magnesium nitrate hexahydrate and oxalic acid as precursors with ethanol as a solvent. The process involves gel formation, drying at 100 °C for 24 h to form magnesium oxalate dihydrate [α-MgC₂O₄·2H₂O] and its decomposition at 500, 600, 800, and 1000 °C for 2 h to yield MgO powder (average crystallite size ∼6.5-73.5 nm). The sol-gel products at various stages of synthesis are characterized for their thermal behaviour, phase, microstructure, optical absorption, and presence of hydroxyl and other groups like OCO, CO, C-C, etc. MgO powder is shown to possess an f.c.c. (NaCl-type) structure with lattice parameter increasing with decrease in crystallite size (t_av); typical value being ∼4.222(2) Å for t_av∼6.5 nm as against the bulk value of 4.211 Å. Infrared absorption has shown MgO to be highly reactive with water. Also, a variety of F- and M-defect centres found in MgO produce energy levels within the band gap (7.8 eV), which make it attractive for application in plasma displays for increasing secondary electron emission and reducing flickering effects. The possible application of the intermediate sol-gel products, viz., α-MgC₂O₄·2H₂O and anhydrous magnesium oxalate (MgC₂O₄) in understanding the plants and ESR dosimetry, respectively, has also been suggested.     

Characterization of water exposed plasma sprayed oxide coating materials using XPS

The surface compositions and oxidation states of non-exposed and water exposed plasma sprayed oxide coatings were studied using X-ray photoelectron spectroscopy (XPS). Coating materials were TiO₂, Al₂O₃ and Cr₂O₃ and their mixtures. Water exposures were performed for free standing coating disks at mild electrolyte (1 mmol NaCl solution) at pH 4, 7 and 9. The exposure time was two weeks.It was observed that pure plasma sprayed TiO₂ material was chemically stable over whole experiment pH range and only slight surface hydroxylation was observed for this material.In case of plasma sprayed Al₂O₃ materials the surface O/Al ratio increased considerably during water exposure especially at exposure pH 7. This was probably result of surface conversion to hydrous form. No surface oxidation state changes were observed for this material.The non-exposed Cr₂O₃ materials contained both Cr(III) and Cr(VI) oxides. The water exposures increased the surface oxygen and Cr(VI) contents at the expense of Cr(III). The most probable reason for that was the dissolution of surface Cr(VI) oxide phase during water exposures and the (re)adsorption of dissolved Cr(VI) species back to the surface.     

Formation of a high hydrophilic/hydrophobic contrast surface on PET substrates by ECR generated sulfur hexafluoride plasma

High hydrophilic/hydrophobic contrast surfaces on polyethylene terephthalate (PET) substrates were formed by shadow mask technique in electron cyclotron resonance generated sulfur hexafluoride plasma atmosphere. The X-ray photoelectron spectroscopy (XPS) analyses indicate that the unmasked PET surfaces contained a high proportion of the CF₂-CF₂ groups, and therefore were hydrophobic with large water contact angle. However, the surface wettability was found to increase drastically on the masked PET surfaces. This could be resulted from a mass of COF (acid fluoride) compounds observed by XPS on the masked film surfaces. The COF compounds could react with atmospheric moisture to form -COOH groups, which in turn increased the surface wettability. In addition, the surface wetting property of the masked areas was found to change significantly with the plasma treatment time, the mask-to-substrate distance and the storage time after the treatment. The best contract in water contact angle obtained from the treated PET samples was larger than 100° after 168 h of storage.     

Surface modification of porous poly(tetrafluoraethylene) film by a simple chemical oxidation treatment

A simple, inexpensive and environmental chemical treatment process, i.e., treating porous poly(tetrafluoroethylene) (PTFE) films by a mixture of potassium permanganate solution and nitric acid, was proposed to improve the hydrophilicity of PTFE. To evaluate the effectiveness of this strong oxidation treatment, contact angle measurement was performed. The effects of treatment time and temperature on the contact angle of PTFE were studied as well. The results showed that the chemical modification decreased contact angle of as-received PTFE film from 133 ± 3° to 30 ± 4° treated at 100 °C for 3 h, effectively converting the hydrophobic PTFE to a hydrophilic PTFE matrix. The changes in chemical structure, surface compositions and crystal structure of PTFE were examined by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), environmental scanning electron microscopy (ESEM), X-ray diffraction (XRD), respectively. It was found that the F/C atomic ratio decreased from untreated 1.65-0.10 treated by the mixture at 100 °C for 3 h. Hydrophilic groups such as carbonyl (CO) and hydroxyl (OH) were introduced on the surface of PTFE after treatment. Furthermore, hydrophilic compounds K_0.27MnO₂·0.54H₂O was absorbed on the surface of porous PTFE film. Both the introduction of hydrophilic groups and absorption of hydrophilic compounds contribute to the significantly decreased contact angle of PTFE.     

Study on bacteria adherence properties of Mo surface-modified layer in Ti6Al4V alloy prepared by plasma surface alloying technique

Mo surface-modified layer in Ti₆Al₄V alloy was prepared using plasma surface alloying technique. Microstructure of the modified layer was analyzed using X-ray photoelectron spectroscopy (XPS), rough-meter and GDA750 glow discharge optical emission spectrometer. Phase composition of the Mo surface-modified layer was characterized by D/max 2500 X-ray diffraction. Results show that the Mo surface-modified layers consist of pure Mo surface layer with 〈1 1 0〉 and 〈2 1 1〉 orientations and diffusion layer. Mo 3d, O 1s, C 1s and Ti 2p, O 1s, C 1s XPS spectra are recorded at topsurface in the Mo-modified layer and titanium substrate respectively. Because of the different roughness and microstructure, the Mo surface-modified layer can to some extent inhibit bacteria adherence.     

Oxygen plasma functionalization of poly(p-phenilene sulphide)

Surface effects during plasma activation of poly(p-phenilene sulphide)—PPS have been studied. Samples that were exposed to weakly ionized highly dissociated oxygen plasma created an inductively coupled radiofrequency discharge with the power of 100 W. The electron density and temperature were measured with a double Langmuir probe and were 4 × 10¹⁵ m⁻³ and 3 eV, respectively, while the neutral atom density was measured with a fiber optics catalytic probe and was 4 × 10²¹ m⁻³. The surface tension was determined by measuring the contact angle of deionized water, while the appearance of surface functional groups was detected by XPS. The surface tension of untreated PPS was 7 × 10⁻³ N/m or/and increased to 7 × 10⁻² N/m in few seconds of plasma treatment. It remained fairly constant for longer plasma treatments. The XPS survey spectrum showed little oxygen on untreated samples, but its concentration increased to about 20 at.% in few seconds. Detailed high resolution XPS C 1s peak showed that the carbon was left fairly stable during plasma treatment. The main functional groups formed were rather sulphate in sulphite groups, as determined from high resolution S 2p peak. Namely, a strong transition from sulphide to sulphate state of sulfur was observed. The spontaneous deactivation of the polymer surface was measured as well. The deactivation was fairly logarithmic with the characteristic decay time of several hours.     

Surface modification of Sylgard 184 polydimethylsiloxane by 254 nm excimer radiation and characterization by contact angle goniometry, infrared spectroscopy, atomic force and scanning electron microscopy

The modification of polydimethylsiloxane (PDMS) by narrow band 254 nm excimer radiation under a nitrogen atmosphere was characterized by contact angle goniometry, attenuated total reflectance infrared spectroscopy, atomic force and scanning electron microscopy. UV irradiation results in the formation of the carboxylic acids that influences the wettability of the surface. Continued exposure results in the formation of an inorganic surface (SiO_x (1 < x < 2)) which hinders the ability to continually increase the wettability. The continuity of this inorganic layer is disrupted by the formation of surface cracks. These results have implications in the fabrication and chemical modification of microfluidic or micro-electro-mechanical systems.