Surface roughness and hydrophilicity enhancement of polyolefin‐based membranes by three kinds of plasma methods

The introduction of antibacterial property, conductivity, wettability and antithrombogenicity into polyolefin‐based membranes has evoked much attention, which can be achieved by coating hydrophilic polymers. Therefore, it is necessary to modify the roughness and hydrophilicity of polyolefin‐based membranes to enhance the coating ability. In this paper, three kinds of plasma methods, including inductively coupled (ICP) plasma, radio frequency low pressure (RFP) plasma and atmospheric dielectric barrier discharge (DBD) plasma, were used to modify the surface of the polyethylene (PE), polypropylene (PP) and polyester‐polypropylene (PET–PP) membranes. The surface roughness of the plasma‐modified PE, PP and PET–PP films was investigated by scanning electron microscopy (SEM) and atomic force microscope (AFM). The polar functional groups of films were observed by energy dispersive spectrometer (EDX) and X‐ray photoelectron spectroscopy (XPS). Besides, the hydrophilicity of the plasma‐modified PE, PP and PET–PP films was evaluated by water contact angle measurement. It was found that the surface roughness and hydrophilicity of plasma‐modified PE, PP and PET–PP films increased with the generation of oxygen‐containing functional groups (i.e. C―O, and C?O). The PET–PP membranes were treated by RFP plasma at different processing powers and times. These results indicated that plasma is an effective way to modify films, and the treatment time and power of plasma had a certain accumulation effect on the membranes' hydrophilicity. As for the roughness and hydrophilicity, the DBD plasma modifies the PE film, which is the optimum way to get the ideal roughness and hydrophilicity. Copyright © 2015 John Wiley & Sons, Ltd.     

Diagnostics of Plasma Behavior and TiO<Subscript>2</Subscript> Properties Based on DBD/TiO<Subscript>2</Subscript> Hybrid System

Plasma catalysis is gaining increasing interest in environmental and energy applications, such as the destruction of gas pollutants and hydrocarbon conversion. In order to further improve the application of plasma catalysis, it is crucial to understand the fundamental mechanisms, especially the mutual interaction between plasma and catalyst. In this paper, a parallel-plate dielectric barrier discharge (DBD) reactor is developed to investigate the plasma behavior and TiO₂ properties in the plasma/catalytic hybrid system. The introduction of TiO₂ thin film coated on the dielectric improves the discharge intensity, which significantly contributes to the enhancement of reactive species and charges. The energy efficiency of generating ozone in DBD/TiO₂ system has been approximately raised by 38% compared to pure DBD when the applied voltage reaches 13 kV. It is fortunately found that the discharge does not change the crystal structure of the TiO₂, but the band gap increases from 3.13 to 3.39 eV, which has been proved to enhance the oxidizability of TiO₂ in the degradation of methyl orange experiment under UV light. The FTIR and XPS spectra also demonstrate that N element is doped into the structure of TiO₂. These results successfully illustrate the plasma behavior and catalyst properties in plasma/catalysis hybrid system and provide reference for the optimization of the plasma catalysis process.     

Surface Modification of Banana Fibers by DBD Plasma Treatment

Banana fibers, an environmentally friendly raw material freely available, were physically modified by atmospheric dielectric barrier discharge (DBD) plasma treatment of different dosages. The influence of the plasma treatment applied on the banana fibers was performed considering the mechanical properties, wettability, chemical composition and surface morphology. These properties were evaluated by tensile tests, static and dynamic contact angle, Fourier transform infrared spectroscopy, energy dispersive spectroscopy, X-ray diffractometry, conductivity and pH of aqueous extract, differential scanning calorimetry and scanning electron microscopy images. We compare untreated and treated fibers with three different DBD plasma dosages. The results of this study showed considerable modifications in banana fibers when these are submitted to plasma treatment.     

Catalytic Properties of TiO<Subscript>2</Subscript>/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles in Plasma Chemical Treatment

We proposed here a new process coupling dielectric barrier discharge (DBD) plasma with magnetic photocatalytic material nanoparticles for improving yield in DBD degradation of methyl orange (MO). TiO₂ doped Fe₃O₄ (TiO₂/Fe₃O₄) was prepared by the sol-gel method and used as a new type of magnetic photocatalyst in DBD system. It was found that the introduction of TiO₂/Fe₃O₄ in DBD system could effectively make use of the energy generated in DBD process and improve hydroxyl radical contributed by the main surface Fenton reaction, photocatalytic reaction and catalytic decomposition of dissolved ozone. Most part of MO (88%) was degraded during 30 min at peak voltage of 13 kV and TiO₂/Fe₃O₄ load of 100 mg/L, with a rate constant of 0.0731 min^?1 and a degradation yield of 7.23 g/(kW h). The coupled system showed higher degradation efficiency for MO removal.     

Surface modification of PET films by atmospheric pressure plasma exposure with three reactive gas sources

The surface modification of poly (ethylene terephthalate) (PET) film was carried out using an atmospheric pressure plasma (APP) jet device with three reactive gases: air, N₂, and Ar. The water contact angles on the PET film were found to decrease considerably after the APP exposure. The changes in the advancing and receding contact angles of water on the APP-exposed PET film with aging time were examined by the wetting force measurements employing the Wilhelmy method. The hydrophobic recovery due to the rinsing with water as well as the aging in air was observed only for the advancing angle, which was probably caused by the dissolution of low molecular weight oxidized materials into water, the loss of volatile oxidized species to the atmosphere and the reorientation and the migration of polymer chains. The wettability and the surface free energy of the APP-exposed PET film after diminishing hydrophobic recovery was sufficiently large compared with the untreated film. X-ray photoelectron spectroscopy confirmed that the PET film surface was oxidized due to the APP exposure. When N₂ gas was used for the APP exposure, the surface nitrogen concentration was found to increase with decreasing D. The surface oxygen concentration on the APP-exposed PET film was reduced by rinsing with water, in accordance with the hydrophobic recovery behavior. From atomic force microscopy, surface topographical change due to the APP exposure was observed. The changes in the PET surface properties due to the APP exposure as mentioned above were remarkable for using N₂ gas.     

Dielectric properties and I-V characteristics of (Pb<Subscript>0.4</Subscript>Sr<Subscript>0.6</Subscript>)TiO<Subscript>3</Subscript> thin films improved by TiO<Subscript>2</Subscript> buffer layers

A TiO₂ thin buffer layer was introduced between the (Pb_0.4Sr_0.6)TiO₃ (PST) film and the Pt/Ti/SiO₂/Si substrate in an attempt to improve their electrical properties. Both TiO₂ and PST layers were prepared by a chemical solution deposition method. It was found that the TiO₂ buffer layer increased the (100)/(001) preferred orientation of PST and decreased the surface roughness of the films, leading to an enhancement in electrical properties including an increase in dielectric constant and in its tunability by DC voltage, as well as a decrease in dielectric loss and leakage current density. At an optimized thickness of the TiO₂ buffer layer deposited using 0.02 mol/l TiO₂ sol, the 330-nm-thick PST films had a dielectric constant, loss and tunability of 1126, 0.044 and 60.7% at 10 kHz, respectively, while the leakage current density was 1.95 × 10⁻⁶ A/cm² at 100 kV/cm.     

Improving surface quality of polyethylene terephthalate film for large area flexible electronic applications

Lamination is a method utilized to protect flexible electroluminescence device against environmental hazards, such as dust, moisture, and water vapor. The materials are typically joined together using adhesive or cohesion of the materials during the lamination process. Polyethylene terephthalate (PET) is commonly used as the substrate film where electroluminescence patterns are printed. However, PET film has a relatively low surface energy and high contact angle, which would cause relatively weak laminating strength. This paper discusses the use of atmospheric plasma as a surface treatment method to modify PET and laminating films’ interface to improve bonding and laminating quality. Experimental results revealed that atmospheric plasma process reduced the contact angle of both PET and laminating films. Functional groups favoring hydrophilicity were found on the films’ interface after the atmospheric plasma treatment. These effects consequently increased surface energies of both films and favored bonding between the films. The treated films thus had increased laminating strength by approximately six times without compromising the transparency quality.     

Silicon Dioxide Coating of Titanium Dioxide Nanoparticles from Dielectric Barrier Discharge in a Gaseous Mixture of Silane and Nitrogen

The coating of titanium dioxide nanoparticles with silicon dioxide has been carried out by dielectric barrier discharge (DBD) plasma treatments to enhance the thermostability of Titania for applications at high temperature processes. During the first coating processing step, a closed film of silicon nitride was produced via plasma treatment in a gaseous mixture of silane and nitrogen, while atmospheric surface contaminations got mainly removed. In the second processing step, the DBD plasma treatment in oxygen or air was used to convert the silicon nitride mainly into silicon dioxide. Remaining carbon impurities at the interfaces between titanium dioxide and silicon nitride after the nitrogen/silane plasma treatment were subsequently removed simultaneously. Atomic force microscopy and X-ray photoelectron spectroscopy were employed to study the DBD plasma treatments of the TiO₂ nanoparticles.     

Biaxially Oriented Polypropylene (BOPP) Surface Modification by Nitrogen Atmospheric Pressure Glow Discharge (APGD) and by Air Corona

We compare two surface treatments of biaxially-oriented polypropylene (BOPP), which are carried out in the same dielectric barrier discharge (DBD) apparatus, namely air corona, and N₂ atmospheric pressure glow discharge (APGD). Changes in the surface energy and chemistry are investigated by contact angle measurements, by X-ray photoelectron spectroscopy (XPS) and by attenuated total reflectance infrared spectroscopy (ATR-FTIR). It is shown that N₂ APGD treatment leads to a higher surface energy than air corona treatment, and to the formation of mostly amine, amide, and hydroxyl functional groups at the polypropylene surface. Finally, hydrophobic recovery of the treated film is studied; for both treatment types, the increased surface energy is found to decay in a similar manner with increasing storage time after treatment.     

Comparison of the surface characteristics of polypropylene films treated by Ar and mixed gas (Ar/O2) atmospheric pressure plasma

In an attempt to modify the hydrophobic surface properties of polypropylene (PP) films, this study examined the optimum process parameters of atmospheric pressure plasma (APP) using Ar gas. Under optimized conditions, the effects of a mixed gas (Ar/O2) plasma treatment on the surface-free energy of a PP film were investigated as a function of the O2 content. The polar contribution of the surface-free energy of the PP film increased with increasing O2 content in the gas mixture. However, slightly more oxygen-containing polar functional groups such as CO, CO, and COO were introduced on the PP film surface by the Ar gas only rather than by the Ar/O2 gas mixture. In addition, AFM analysis showed that the Ar plasma treatment of the PP film produced the smoothest surface as a result of the relatively homogeneous etching process.     

In‐depth diffusion of oxygen into LDPE exposed to an Ar–O2 atmospheric post‐discharge: a complementary approach between AR‐XPS and Tof‐SIMS techniques

The in‐depth oxygen diffusion into a low density polyethylene film is performed in the post‐discharge of an atmospheric plasma torch, supplied in argon as carrier gas and with or without oxygen as reactive gas. The chemical and structural properties of the polymer surface and bulk are studied in terms of plasma parameters (treatment time, power, and reactive gas flow rate). A good correlation between XPS and Fourier transform infrared spectroscopy analyses is demonstrated. The penetration depth of oxygen into the bulk of the polymer is investigated by angle resolved‐XPS and time‐of‐flight SIMS. It is shown that, depending on the plasma conditions, oxygen could penetrate up to 20–40 nm into the low density polyethylene during the atmospheric plasma treatment. Copyright © 2014 John Wiley & Sons, Ltd.     

Wettability characterization of transparent MgF<Subscript>2</Subscript> nanoparticle coatings with SiO<Subscript>2</Subscript> binder covered with fluoroalkylsilane self-assembled monolayers

SiO₂-added MgF₂ nanoparticle coatings with various surface roughness properties were formed on silica-glass substrates from autoclaved sols prepared at 100–180 °C. The samples were exposed to fluoro-alkyl silane (FAS) vapor to give hydrophobicity. All nanoparticle samples before FAS treatment had transmittances higher than 93% and such values were preserved even after FAS treatment. We examined root mean square roughnesses of the nanoparticle coatings with a Scanning Probe Microscope. We also examined their static and dynamic wettabilities with a contact angle meter and calculated their adhesive energies and surface free energies (SFEs). The surface roughness of the nanoparticle coating increased with the increase of the autoclave temperature. In addition, higher autoclave temperature caused increases in the sliding angle and decreases in the SFE. Interestingly, the higher the contact angle was, the larger the sliding angle was, although smaller sliding angle was expected with a larger contact angle.     

Low-temperature processing of sol-gel derived Pb(Zr,Ti)O<Subscript>3</Subscript> thick films using CO<Subscript>2</Subscript> laser annealing

Fabrication of ferroelectric Pb(Zr_0.52Ti_0.48)O₃ (PZT) thick films on a Pt/Ti/SiO₂/Si substrate using powder-mixing sol-gel spin coating and continuous wave CO₂ laser annealing technique to treat the specimens with at a relatively low temperature was investigated in the present work. PZT fine powders were prepared by drying and pyrolysis of sol-gel solutions and calcined at temperatures from 400 to 750°C. After fine powder-containing sol-gel solutions were spin-coated on a substrate and pyrolyzed, CO₂ laser annealing was carried out to heat treat the specimens. The results show that laser annealing provides an extremely efficient way to crystallize the materials, but an amorphous phase may also form in the case of overheating. Thicker films absorb laser energy more effectively and therefore melt at shorter periods, implying a significant volume effect. A film with thickness of 1 μm shows cracks and rough surface morphology and it was difficult to obtain acceptable electrical properties, indicating importance of controlling interfacial stress and choosing appropriate size of the mixing powders. On the other hand, a thick film of 5 μm annealed at 100 W/cm² for 15 s exhibits excellent properties (P _r = 36.1 μC/cm², E _c = 19.66 kV/cm). Films of 10 μm form a melting zone at the surface and a non-crystallized bottom layer easily at an energy density of 100 W/cm², showing poor electrical properties. Besides, porosity and electrical properties of thick films can be controlled using appropriate processing parameters, suggesting that CO₂ laser annealing of modified sol-gel films is suitable for fabricating films of low dielectric constants and high crystallinity.     

Deposition of polysiloxane‐like nanofilms onto an aluminium alloy by plasma polymerized hexamethyldisiloxane: characterization by XPS and contact angle measurements

In this work, aluminium (Alclad 2024‐T3) substrates were cleaned by an r.f. (13.56 MHz) plasma, using argon (Ar), oxygen (O₂) and a mixture of O₂/Ar (50:50) gases. The effectiveness of plasma cleaning was checked in situ using X‐ray photoelectron spectroscopy (XPS) and ex situ using water contact angle measurements. XPS O/Al surface atomic ratios are in excellent agreement with those of the crystalline boehmite and the pseudoboehmite. Oxygen O 1s peak‐fitting was used to quantify the proportion of hydroxyl ions and the functional composition on the aluminium surface: the surface cleaned with O₂ plasma contains 50% of aluminium hydroxides, the ones cleaned with Ar plasma and with Ar/O₂ plasma contain, respectively, 25 and 37% hydroxyl ions. The binding energy separation between Al 2p and O 1s is characteristic of AlO(OH). Thin SiO_x films were subsequently deposited from a mixture of hexamethyldisiloxane (HMDSO) and oxygen. In the absence of oxygen, a hydrophobic (Θ≥ 100° ) film characteristic of polydimethylsiloxane (PDMS) is formed: polysiloxane‐like thinner films (SiO_x) are obtained with the introduction of oxygen. XPS and contact angle measurements confirmed both the composition and the structure of these films. More importantly, contact angle measurements using different liquids and interpreted with the van Oss‐Good‐Chaudhury theory allowed determination of the surface free energy of the deposited films: the calculated values of surface tension of the film formed from HMDSO/O₂: (50/50) are in excellent agreement with those of reference silica‐based materials such as a silicon wafer and cleaned glass. Copyright © 2007 John Wiley & Sons, Ltd.     

Surface Modification of Silicone Rubber by CF<Subscript>4</Subscript> Radio Frequency Plasma Immersion

Silicone rubber samples were treated by 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, respectively. Static contact angle, ATR-FTIR and XPS, and AFM were employed to characterize the changes of surface on hydrophobicity, functional groups, and topography. The results indicate the static contact angle is improved from 100.7 to 150.2°, and the super-hydrophobic surface, which corresponds to a static contact angle of 150.2°, appears at RF power of 200 W for a 5 min treatment time. It is suggested that the formation of super-hydrophobic surface is ascribed to the co-action of the increase of surface roughness created by the ablation reaction of CF₄ plasma and the formation of [–SiF _x (CH₃)_2−x –O–] _n (x = 1, 2) structure produced by the direct attachment of F atoms to Si.     

Study of the wettability properties of polypropylene nonwoven mats by low‐pressure oxygen plasma treatment

Surface modification by plasma treatment is widely used for textiles and polymeric materials. Plasma processes are environmentally friendly and reduce chemicals and energy consumption. This study reports the effect of cold, low‐pressure oxygen plasma on the wettability properties of polypropylene (PP) nonwoven mats. The wetting properties were examined using contact angle, surface energy, and diameters of the drop after 20 s of treatment. It was found that plasma treatment had a significant effect on the wettability of PP fibers. The ageing for 90 days had no significant effect on the wettability. It was also shown that the morphology of the fibers was not affected by the plasma treatment. Copyright © 2007 John Wiley & Sons, Ltd.     

Influence of O2 Plasma on Surface Properties of PC-TiO2 Nanocomposite Film

In this work, polycarbonate-TiO₂ nanocomposite films were prepared with different percentages. The aim was to consider the effect of O₂ LF plasma (50 Hz) on the hydrophilicity, surface energy, and surface morphology of polycarbonate and polycarbonate-TiO₂ nanocomposite. Structure of samples was determined by using X-ray diffraction analysis. In comparison with the reference sample, the samples’ structure did not change after plasma treatment. Surface properties of polycarbonate and polycarbonate-TiO₂ nanocomposite films were studied by X-ray photoelectron spectroscopy (XPS), contact angle measurement, atomic force microscopy (AFM), and Vickers microhardness tester. XPS analysis showed that the surface of samples became more oxidized due to plasma treatment. The water contact angle significantly decreased from 88° to 15° after plasma treatment. It was observed that the hardness of the nanocomposite films was not modified after plasma treatment.     

Chemical solution processing and characterization of Ba(Zr,Ti)O<Subscript>3</Subscript>/LaNiO<Subscript>3</Subscript> layered thin films

Ba(Zr,Ti)O₃/LaNiO₃ layered thin films have been synthesized by chemical solution deposition (CSD) using metal-organic precursor solutions. Ba(Zr,Ti)O₃ thin films with smooth surface morphology and excellent dielectric properties were prepared on Pt/TiO _x /SiO₂/Si substrates by controlling the Zr/Ti ratios in Ba(Zr,Ti)O₃. Chemically derived LaNiO₃ thin films crystallized into the perovskite single phase and their conductivity was sufficiently high as a thin-film electrode. Ba(Zr,Ti)O₃/LaNiO₃ layered thin films of single phase perovskite were fabricated on SiO₂/Si and fused silica substrates. The dielectric constant of a Ba(Zr_0.2Ti_0.8)O₃ thin film prepared at 700°C on a LaNiO₃/fused silica substrate was found to be approximately 830 with a dielectric loss of 5% at 1 kHz and room temperature. Although the Ba(Zr_0.2Ti_0.8)O₃ thin film on the LaNiO₃/fused silica substrate showed a smaller dielectric constant than the Ba(Zr_0.2Ti_0.8)O₃ thin film on Pt/TiO _x /SiO₂/Si, small temperature dependence of dielectric constant was achieved over a wide temperature range. Furthermore, the fabrication of the Ba(Zr,Ti)O₃/LaNiO₃ films in alternate thin layers similar to a multilayer capacitor structure was performed by the same solution deposition process.     

Copper nanowire arrays surface wettability control using atomic layer deposition of TiO<Subscript>2</Subscript>

Template two step electrodeposition method and atomic layer deposition were used to synthesize copper nanowires of varied length (1.2 to 26.2 μm) and copper nanowires coated with titanium dioxide. As a result of the atomic layer deposition of TiO₂, coated nanowires demonstrated an up to 10-fold decrease in the wetting angle, compared with uncoated nanowires. It was found the dissipation rate is substantially higher for nanowires coated by the atomic layer deposition method (100 s) as compared with the uncoated copper nanowires (400 s), which assumes the positive properties of water propagation along the surface, necessary for improving the heat transfer. It was also found that the water contact angle for uncoated nanowires and those coated with TiO₂ by the atomic layer deposition (ALD) gradually increases as the samples are kept in air. A gradual increase in wettability was also observed for smooth silicon wafers coated by ALD of TiO₂, which were exposed to air. On the coated silicon substrates, the wetting angle gradually increased from 10° to approximately 56° in the course of four days. In addition, it was shown that copper nanowires coated with TiO₂ by the atomic layer deposition method have an excellent corrosion resistance, compared with uncoated nanowires, when brought in contact with air and water.     

Oxidative Conversion of PFC via Plasma Processing with Dielectric Barrier Discharges

Perfluorocompounds (PFCs) have been extensively used as plasma etching andchemical vapor deposition (CVD) gases for semiconductor manufacturingprocesses. PFCs have significant effects on the global warming and havevery long atmospheric lifetimes. Laboratory-scale experiments were performedto evaluate the effectiveness of CF4 conversion by using dielectric barrierdischarges (DBD). The results of this study revealed that the removalefficiency of CF₄ increased with application of higher voltage, gas residence time, oxygen content, and frequency. Combined plasma catalysis(CPC) is an innovative way for abatement of PFC and experimental results indicated that combining plasma with catalysts could effectively remove CF4. Products were analyzed by Fourier transform–infrared spectroscopy (FT–IR) and the major products of the CF4 processing with DBD were CO2, COF2, and CO, when O was included in the discharge process. Preliminary results indicated that as high as 65.9% of CF4 was decomposed with CPC operated at 15 kV, 240 Hz for the gas stream containing 300 ppmv CF₄,20% by volume O₂, and 40% by volume Ar, with N₂ as thecarrier gas.