Air Plasma Treatment Research Articles

Ultrafast, Reversible Transition of Superwettability of Graphene Network and Controllable Underwater Oil Adhesion for Oil Microdroplet Transportation

AbstractRecently, reversible surface superwettability has attracted enormous interest, and methods to shorten the cycle time of transition have also garnered the attention of researchers. Herein, a superhydrophobic, open‐cell graphene network (OCGN) is fabricated via self‐assembly of graphene oxide and vapor ejection. Owing to the special open‐cell microstructure, the OCGNs can be transformed to be superhydrophilic rapidly within only 1 s by air plasma treatment. Moreover, the OCGNs with pure graphene composition have a high conductivity and show an ultrafast Joule heating rate of up to 20 °C s−1 at a voltage of 20 V. By means of this property, for the first time an ultrafast recovery of the superhydrophobicity for OCGNs by self‐induced Joule heating with the shortest time of 1 min is reported. The mechanism of ultrafast, reversible transition is also explored specifically in this study. In addition, the superhydrophilic OCGNs show superoleophobicity in water and their underwater adhesion for oil droplets can be controlled by plasma treatment. Finally, the OCGNs with different oil adhesion properties are fabricated and the underwater oil microdroplet transportation is realized using OCGNs. Therefore, the OCGNs with smart surface can be an excellent candidate for achieving multifunctional superwettability of surfaces.

Quantification and physics of cold plasma treatment of organic liquid surfaces

Plasma treatment increases the surface energy of condensed phases: solids and liquids. Two independent methods of the quantification of the influence imposed by a cold radiofrequency air plasma treatment on the surface properties of silicone oils (polydimethylsiloxane) of various molecular masses and castor oil are introduced. Under the first method the water droplet coated by oils was exposed to the cold air radiofrequency plasma, resulting in an increase of oil/air surface energy. An expression relating the oil/air surface energy to the apparent contact angle of the water droplet coated with oil was derived. The apparent contact angle was established experimentally. Calculation of the oil/air surface energy and spreading parameter was carried out for the various plasma-treated silicone and castor oils. The second method is based on the measurement of the electret response of the plasma-treated liquids.

Surface Modification of Polystyrene Coating on QCM Sensor using Ambient Air Plasma at Low Pressure

Surface modification of quartz crystal microbalance Quartz Crystal Microbalance (QCM) sensor is crucial in the development of QCM sensor as a basis for biosensor and chemical sensor. Plasma technology has been used widely for surface modification such as cleaning, activation, deposition, etching, and ashing. In this work, we used ambient air plasma treatment to modify the hydrophobicity of polystyrene coating on the QCM sensor. The QCM sensor was coated with polystyrene using a spin coating and then heated at 200 °C. The plasma was generated in a low pressure (60 Pa) chamber filled with ambient air at a flow rate of 50 sccm. The power was supplied by a 2 MHz RF generator. The sensor was treated in air plasma chamber for 5 minutes. The result shows that variation in DC offset affects the hydrophobicity of the polystyrene surface. Under plasma exposure without DC bias, the polystyrene surface changes to hydrophilic significantly indicated by lower contact angle compare to the non-treated surface. There is no electrical impedance change of the QCM sensor with polystyrene coating before and after plasma treatment. It indicates that the acoustic impedance as a mechanical property of the polystyrene film on top of the QCM sensor remains.

Surface modification of porous PLGA scaffolds with plasma for preventing dimensional shrinkage and promoting scaffold-cell/tissue interactions.

Due to numerous merits, polyesters have been widely used for the preparation of porous scaffolds for biomedical applications. However, insufficient dimensional stability and weak cell interaction are two critical challenges to highly porous polyester scaffolds fulfilling their roles during applications. Here, we report the surface modification of PLGA scaffolds with air plasma for simultaneously tackling the dimensional shrinkage of PLGA scaffolds and improving scaffold-tissue integration. Highly porous PLGA scaffolds with interconnected pore structures and well orientated microtubules were prepared through lyophilization, and an air plasma process with varied duration was applied to the porous scaffolds. Water contact angle measurements indicated that moderate treatment (120 seconds) can significantly increase the wettability without distorting the morphology of and damaging the PLGA scaffolds. Further characterization (SEM, XPS, μ-CT, and theoretical computations) revealed that the plasma treatment enabled the generation of carboxyl groups on the surface of the PLGA scaffold, and the hydrophilic PLGA chain tends to extend under aqueous conditions in comparison to the hydrophobic pristine PLGA chain. Consequently, this could eliminate the hydrophobic-scaffold/water interface and weaken the driving force behind the distortion of the scaffolds in aqueous conditions, and finally inhibit overall shrinkage and maintain the microstructures of the porous scaffolds. Similar results were observed with porous PLA scaffolds, indicating the generality of air plasma treatment in inhibiting the shrinkage of polyester scaffolds. In the meantime, in vitro cell attachment experiments and in vivo subcutaneous implantation results consistently indicated that better maintaining the microstructure could significantly enhance the short-term cell attachment/proliferation on the scaffold and the long-term scaffold-tissue integration. These findings may inspire many creative and efficient strategies for the surface modification of polyester scaffolds to improve their performance for biomedical applications.

Bacteria inactivation by atmospheric pressure plasma jet treatment

Atmospheric pressure plasmas have achieved great scientific and technological advances for a wide range of applications including the field of antimicrobial treatment. In this paper, a home-made atmospheric pressure plasma jet device was built and the effects of air plasma treatments on the inactivation of pure bacterial culture (Escherichia coli ATCC 8739) deposited onto the surface of agar plates were investigated. Plasmas were generated using high voltage discharge for 30, 60 and 90 s. The number of viable microorganisms was determined using a plate count method. Microbial Log10 reduction depended on the time of exposure and feed gas flow. A significant reduction of about 2.5 Log10 for E. coli was achieved within 60 s of plasma treatment. This result can be related to the presence of reactive species in the plasma volume, in particular, O radicals.

Air plasma treatment of aluminium trihydrate filled poly(methyl methacrylate)

Air plasma treatments of aluminium trihydrate filled poly(methyl methacrylate) polymer (PMMA) composites were carried out in a dielectric barrier discharge. X-ray photoelectron spectroscopy (XPS) and attenuated total reflection – infrared spectroscopy have been employed to analyse the changes in chemical composition. Confocal laser-scanning microscopy and atomic force microscopy yielded the impact on surface structure and morphology. Surface free energy (SFE) measurements and adhesive bond strength tests were used to correlate the results to possible applications like gluing and lacquering. The plasma treatments resulted mainly in an etching of the matrix polymer and a minor chemical modification. An apparent contradiction of XPS, ATR and SFE results was attributed to a re-polymerization and re-deposition of the etched PMMA material as debris back onto the surface. This effect, which is seldom taken into account, annihilated the positive impact of the plasma treatment due to the debris acting as rated break point.

The Effect of Plasma Treated PLGA/MWCNTs-COOH Composite Nanofibers on Nerve Cell Behavior.

Electrospun nanofibrous scaffolds which can mimic the architecture of the natural extracellular matrix (ECM) are potential candidates for peripheral nerve repair application. Multi-walled carbon nanotubes (MWCNTs) are used in peripheral nerve repair due to their ability to promote neurite extension and support neural network formation. In this study, surface-modified nanofibrous scaffolds composed of poly(lactic-co-glycolic acid) (PLGA) and various ratios of carboxyl-modified MWCNTs (MWCNTs-COOH) (PC0, PC2, PC4 and PC8) were fabricated by electrospinning. The effects of MWCNTs-COOH on the fibers’ morphology, diameter distribution, mechanical properties and surface hydrophilicity were characterized by Scanning Electron Microscopy (SEM), ImageJ software, tensile testing and water contact angle. Furthermore, air plasma treatment was applied to improve the surface hydrophilicity of the scaffolds, and the optimal treatment condition was determined in terms of surface morphology, water contact angle and PC12 cell adhesion. Plasma treated nanofibers (p-PC0, p-PC2, p-PC4 and p-PC8) under optimal treatment conditions were used for further study. PC12 cell proliferation and differentiation were both improved by the addition of MWCNTs-COOH in scaffolds. Additionally, the proliferation and maturation of Schwann cells were enhanced on scaffolds containing MWCNTs-COOH. The neurite outgrowth of rat dorsal root ganglia (DRG) neurons was promoted on MWCNTs-COOH-containing scaffolds, and those cultured on p-PC8 scaffolds showed elongated neurites with a length up to 78.27 μm after 3 days culture. Our results suggested that plasma treated nanofibers under appropriate conditions were able to improve cell attachment. They also demonstrated that plasma treated scaffolds containing MWCNTs-COOH, especially the p-PC8 nanofibrous scaffold could support the proliferation, differentiation, maturation and neurite extension of PC12 cells, Schwann cells and DRG neurons. Therefore, p-PC8 could be a potential candidate for peripheral nerve regeneration application.

EIS in SKP študija izboljšanja zaščite z alkidno prevleko, modificirano s plazemsko obdelavo na Q235 jeklu

EIS in SKP študija izboljšanja zaščite z alkidno prevleko, modificirano s plazemsko obdelavo na Q235 jeklu

Characterization of fracture energy and toughness of air plasma PDMS–PDMS bonding by T-peel testing

The fracture energy, toughness and failure modes of air plasma oxidized polydimethylsiloxane (PDMS) bonding are evaluated in this paper. Each PDMS–PDMS bonded specimen was subjected to T-peel testing at a constant-displacement rate. The load–extension curve from each test was analyzed by the principle of energy balance in linearly elastic fracture mechanics, to calculate the fracture energy (critical strain energy), which is the maximal strain energy a bonded specimen can withstand without losing its assembly integrity, and toughness (surface energy), which is the bonding energy at the interface. A distribution of calculated values against the air plasma treatment parameters shows the predominant range of 0.1 to 0.4 N/mm for fracture energy and 0.1 to 0.2 N/mm for toughness. Together with an analysis of three failure modes (cohesive, adhesive, and mixed), the results suggest 0.1 N/mm as the threshold of the fracture energy for weak bonding, below which a specimen will be likely to fail through debonding. A set of treatment parameters are recommended for using air plasma to achieve strong bonding.

Quantitative characterization of plasma treated PDMS microfluidic substrates by inverse gas chromatography

Abstract The effect of air plasma exposure time on the surface energies and acid-base characteristics of polydimethylsiloxane (PDMS) particles was studied. Polymerized PDMS powder was radio frequency induced air plasma irradiated for 2–10 s with the power of 500 W. The efficiency of the plasma treatments was investigated by a new generation inverse gas chromatograph, a surface energy analyzer. The dispersive component of surface energy was determined by the Dorris-Gray method describing the van der Waals interactions, while the specific component of surface energy expressed the surface ability for Lewis acid-base interactions. It was demonstrated that the air plasma treatment did not affect the dispersive and acidic parts of the surface energy and the change of surface hydrophilicity was caused by the raise of the electron-donor ability of the PDMS surface, characterized by van Oss-Good-Chaudhury’s base number. The optimal plasma treatment time was found to be 5 s. Analysis of the specific surface energy and acid-base characteristics with respect to exposure time showed that partial to complete hydrophobic recovery occurred within 38 h.

Orienting Silicon-Containing Block Copolymer Films with Perpendicular Cylinders via Entropy and Surface Plasma Treatment

Controlling the orientation of nanostructured block copolymer (BCP) thin films is essential for next-generation lithography. However, obtaining BCP with perpendicular orientation remains a challenge because of the surface selectivity to the different blocks. This challenge is especially severe for silicon-containing BCPs which is notorious for its high surface energy difference between constituted blocks. Here, we demonstrate a new approach to achieve perpendicular orientation with high aspect ratio using a combination of architecture effect (entropy effect) and surface air plasma treatment (enthalpy effect). Specifically, perpendicular cylinders of star-block copolymers composed of polystyrene and poly(dimethylsiloxane) blocks can be formed from the bottom substrate to the top surface of the thin film.

Modification of starch using low pressure radio frequency air plasma

Cold plasma is one of the emerging nonthermal food processing technologies recently drawn interest as a chemical-free biopolymer modification method. In the present study, two starches (corn and tapioca) were exposed to low pressure radio frequency plasma at 40 W and 60 W for 10 and 20 min. The effect of air plasma treatment on the starch properties was determined by measuring amylose content, swelling power, powder flowability properties, gelatinization temperatures and pasting properties. The amylose content of corn and tapioca starches was observed to decreased and increased respectively. Increase in water binding capacity and swelling power of both starches. The results of pH showed partial oxidation of starches as evident from the decrease in pH. Rapid visco analyzer showed an increase in final viscosities after the plasma treatment. The increase in viscosities is the result of higher amounts of leach out of particles from the starch granules. Plasma treated corn starches exhibited lower peak temperatures and enthalpies whereas it increased in tapioca starches. X-ray diffractogram revealed an A-type pattern of both starches and plasma treatment did not show any significant effect on the crystallanity pattern. Cold plasma offers a unique route for starch modification without affecting its bulk properties.

Plasma treatment of bamboo fibers on the tribological property of polyimide composite filled with graphite

This paper is concerned with the effects of the air plasma surface treatment of bamboo fiber on the tribological properties of the bamboo fiber reinforced polyimide (bamboo/polyimide) composites filled with graphite. Plasma treatment and graphite bring positive effect on the improvement of friction reducing and antiwear of bamboo/polyimide composites. And Fourier transform infrared spectroscopy analysis shows that the bamboo fibers have been oxidized and etched by the air plasma treatment. The presence of active groups makes the polarity of the fiber increase, and so the bond property between the fiber and matrix is improved.

Mechanism of Ampicillin Degradation by Non-Thermal Plasma Treatment with FE-DBD

This research focused on determining the effectiveness of non-thermal atmospheric pressure plasma as an alternative to advanced oxidation processes (AOP) for antibiotic removal in solution. For this study, 20 mM (6.988 g/L) solutions of ampicillin were treated with a floating electrode dielectric barrier discharge (FE-DBD) plasma for varying treatment times. The treated solutions were analyzed primarily using mass spectrometry (MS) and nuclear magnetic resonance spectroscopy (NMR). The preliminary product formed was Ampicillin Sulfoxide, however, many more species are formed as plasma treatment time is increased. Ampicillin was completely eliminated after five minutes of air-plasma treatment. The primary mechanism of ampicillin degradation by plasma treatment is investigated in this study.

Surface modification of ultrahigh molecular weight polyethylene by plasma-induced in-situ grafting with vinyl triethoxysilane.

Ultrahigh molecular weight polyethylene (UHMWPE) is an excellent material with high performance, but it is very difficult to covalently introduce functional groups on its surface owing to its inherently inert structure, which constrains its further application. In this study, vinyl triethoxysilane (VTEOS) containing hydrolysable alkoxyl groups was in situ grafted on UHMWPE by air plasma treatment. The plasma treatment conditions for VTEOS grafting were optimized. The structure of the modified UHMWPE was characterized with FTIR and XPS. The relatively high VTEOS content was obtained when the treating conditions were about 20 W, 125 Pa for 10 min. And FTIR results showed that the grafted structure on the surface was stable for long time duration in the ambient environment. After the treatment, the roughness of the surface increased and the water contact angle of the modified sample dropped to 47.5° from 92.8° of the unmodified one. TGA and XRD results indicated that plasma treatment would not change the bulk structure of UHMWPE greatly. Cell culture experiments showed that fibroblasts on the modified samples had notably high viability and proliferation rate with good adhesion shape. Hence, it might be an effective method to improve the surface properties of UHMWPE for biomedical applications by plasma-induced in-situ grafting with VTEOS. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 321-332, 2018.

Low-temperature (70 °C) ambient air plasma-fabrication of inkjet-printed mesoporous TiO2 flexible photoanodes

Titania/silica electron-generating and -transporting nanocomposite 300 nm layers of high porosity were deposited onto ITO/PET flexible foils using inkjet printing. Prior to printing, the ITO surface had been modified by novel low-temperature ambient air roll-to-roll plasma in order to enhance its surface properties by removing carbon and oxygen contaminants, a process that led to rapid improvement of surface energy. Consequently the ITO work function, an important parameter involving charge injection efficiency in energy harvesting systems, increased by 1 eV. Afterwards, the TiO2/methyl-silica ink exhibited excellent wetting on a 2 s plasma-treated ITO surface. The coating was further processed/mineralized by an additional low-temperature ambient air plasma treatment step. The plasma processing of raw photoanodes led to the mineralization of the methyl-silica binder which resulted in the formation of a fully inorganic TiO2/SiO2 mesoporous structure and significantly increased electrophotocatalytic activity, leading to increased photocurrents. The entire two-step plasma process was performed at low-temperature (70 °C) and high speeds, enabling practical applications of such a procedure for large-area fabrication of flexible photoanodes.

Interface Engineering of Perovskite Solar Cells with Air Plasma Treatment for Improved Performance.

For high-efficiency perovskite solar cells (PSCs), interface engineering becomes critical for carrier collection from the active perovskite material to the transport layer. To enhance the power conversion efficiency (PCE), herein we demonstrate a novel method named surface plasma treatment on a mesoporous TiO2 electron-transport layer (ETL) to improve electron extraction and transport properties at the perovskite/TiO2 interface. According to the XPS results, the plasma treatment induced a partial reduction of Ti4+ to Ti3+ within the TiO2 lattice and increased the concentration of oxygen vacancies on the TiO2 surface. Ultraviolet photoelectron spectra (UPS) show that the Fermi level of TiO2 upshifts about 0.2 eV which may effectively promote carrier separation and transfer at the perovskite/TiO2 interface. In addition, these created donor levels of Ti3+ and oxygen vacancies donate extra electrons, increasing the conductivities of TiO2 films and which could further promote transport. The time-resolved photoluminescence spectra (TRPL) confirm that the decay time decreases dramatically from 656 ns to 235 ns after 90 s plasma treatment, which indicates a more efficient electron-transfer process. Based on all the above-mentioned results, a remarkable enhancement in cell efficiency was obtained, such that the average efficiency was improved from 11.5 % to 14.3 % under AM 1.5G irradiation (100 mW cm-2 ).

Evaluation of parameters affecting adhesive strength of high build epoxy coatings on textured and plasma treated metallic substrates

Epoxy coating systems have been used throughout the years for protecting critical industrial assets. To ensure superior coating adhesion and longevity, abrasive blasting has been traditionally employed to texture metallic surfaces. Though a large variety of abrasives are available in the industry, coal slag (aluminium silicate) and garnet (mineral abrasive) have remained popular choices until now owing to their easy availability. However, depleting reserves of coal slag owing to stricter environmental regulations and shortage of good quality garnet have fueled the need to identify substitutes. This work is focused on evaluating the effect of surface texturing on adhesive strength of epoxy coatings using two novel abrasive types – olivine (obtained from dunite rock) and calcium silicate (iron furnace slag) which are available in abundance and present an excellent alternative. The surface textures of various blast cleaned mild steel (A36) and stainless steel (316L) substrates were evaluated using a combination of techniques namely, optical profilometry (spatial parameters), replica tape method as per ASTM D 4417 (Method C) (height parameter) and scanning electron microscopy (Secondary electron imaging/energy dispersive X-ray spectroscopy analyses) for embedded particle composition analysis. Correlations were drawn to the wettability of metallic substrates textured using the selected abrasives. Adhesive strength tests on high build epoxy coatings, performed in accordance with ASTM D4541 revealed exceptional performance using various grades of both olivine and calcium silicate abrasives. The effect of air plasma treatment on adhesive strength of epoxy coatings applied on mild steel substrates were also studied.

Improvement of wettability and absorbancy of textile using atmospheric pressure dielectric barrier discharge

In this study, cotton textile samples, commonly used in making quilt covers were subjected to atmospheric pressure dielectric barrier discharge treatment to study their surface wettability and absorbancy. Samples were treated in the discharge using a rotatory mechanism and the effects of plasma treatment were examined by contact angle measurement and weight measurement. Air plasma treatment was successful in incorporating hydrophilic functional groups on the textile surface due to which wettability as well as absorbancy immediately after the treatment were highly improved. Effects of plasma treatment started to appear only after 20 cycles (9 mins) and got saturated after 24 cycles (10.8 mins) of treatment. The contact angle reduced from 137 ° (untreated sample) to a value less than 30 ° while absorbancy increased by more than two times as compared to untreated sample. Also, the aging behavior of the plasma treated samples were studied for about a week after plasma treatment. It was observed that the induced oxygen containing groups re-oriented into the bulk of the material during their storage in the environment due to which initial properties of the samples recovered gradually. Our results indicate that low temperature plasma can be successfully applied to modify the properties of textiles and textile industries could utilize this by standardization.

Surface chemistry and germination improvement of Quinoa seeds subjected to plasma activation

Plasma treatment is recognized as a suitable technology to improve germination efficiency of numerous seeds. In this work Quinoa seeds have been subjected to air plasma treatments both at atmospheric and low pressure and improvements found in germination rate and percentage of success. Seed water uptake by exposure to water vapor, although slightly greater for plasma treated seeds, did not justify the observed germination improvement. To identify other possible factors contributing to germination, the chemical changes experienced by outer parts of the seed upon plasma exposure have been investigated by X-ray photoemission spectroscopy (XPS) and scanning electron microscopy (SEM-EDX). XPS revealed that the outer layers of the Quinoa plasma treated seeds were highly oxidized and appeared enriched in potassium ions and adsorbed nitrate species. Simultaneously, SEM-EDX showed that the enrichment in potassium and other mineral elements extended to the seed pericarp and closer zones. The disappearance from the surface of both potassium ions and nitrate species upon exposure of the plasma treated seeds to water vapor is proposed as a factor favoring germination. The use of XPS to study chemical changes at seed surfaces induced by plasma treatments is deemed very important to unravel the mechanisms contributing to germination improvement.