Polytetrafluoroethylene surface modification by filamentary and homogeneous dielectric barrier discharges in air

In this paper, polytetrafluoroethylene (PTFE) films are modified using non-equilibrium plasma generated by homogeneous DBD in air at medium pressure, and the results are compared to those treated by using filamentary DBD in air at atmospheric pressure. The surface properties of PTFE films before and after the treatments are studied using contact angle and surface energy measurement, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). It is found that the plasma treatments modify the PTFE surface in both morphology and composition. The PTFE films modified in both treatments show a remarkable decrease in water contact and a remarkable increase in surface energy. XPS analysis reveals that oxygen-containing polar groups are introduced onto the PTFE surface, and SEM analysis shows that the surfaces of the films are etched after both the treatments. It is found that homogeneous DBD is more effective in PTFE surface modification than filamentary DBD as it can make the contact angle decline to a lower level by introducing more oxygen-containing groups, and the possible reason for this effect is discussed.     

Preparation of hydrophobic coating on glass surface by dielectric barrier discharge using a 16 kHz power supply

A 16 kHz power supply was used to investigate the preparation of hydrophobic film on glass surface by means of atmospheric pressure dielectric barrier discharge (DBD). Air nonthermal plasma was induced between the two parallel electrodes with a glass plate as dielectric barrier. The process for hydrophobic film includes two parts: one is plasma pretreatment to produce active layer on glass surface, another is to form hydrophobic film on glass surface by means of the interaction between air plasma and polydimethylsiloxane oil. The surface changes were observed using contact angle measurement and atomic force microscope. The results show DBD can increase surface roughness, and effectively improve glass surface activation and form a hydrophobic coating on glass surface, and it is possibility to prepare hydrophobic glass with middle frequency power supply.     

Formation of hydrophobic coating on PMMA surface using unipolar nanosecond-pulse DBD in atmospheric air

Dielectric barrier discharge (DBD) can modify the material surface and result in complicated physical and chemical reactions to improve the surface hydrophilicity, which is proved to be an effective method for surface modification. Compared with the traditional ac-excitation DBD, the DBD using unipolar pulses can avoid local overheat of microdischarges and can improve discharge efficiency under some conditions. In this paper, DBD excited by repetitive unipolar nanosecond generator was used to improve the hydrophobicity of Plexiglass (PMMA) surface by means of the interaction between air plasma and silicone oil. The output voltage had a rise time of 40 ns and a full width at half maximum of about 70 ns. The surface hydrophobicity of the PMMA, before and after the surface modification, was evaluated via the contact angle measurement under different experimental conditions. The values of the contact angle shown in this paper were the average of eight measured values, and the standard deviations were also calculated. The surface energy including polar and dispersion components was calculated using the measured average contact angles of distilled water and polyethyleneglycol. The results showed that, as the increase of the discharge voltage, the contact angle increased but the surface energy decreased. With the increase of treatment time, the water contact angle of the modified surface increased at the beginning, and it would reach to a maximum at 7.5 min treatment, and then decreased. The effect of pulse frequency on the modification results was different at various treatment times. In addition, the possible physical and chemical reaction among the DBD plasma, silicone oil and the PMMA surface was discussed.     

Statistical analysis of the effect of dielectric barrier discharge (DBD) operating parameters on the surface processing of poly(methylmethacrylate) film

A dielectric barrier discharge (DBD) plasma, operating in air at atmospheric pressure, has been used to induce changes in the surface properties of poly(methylmethacrylate) (PMMA) films. The relative effects that key DBD operating parameters, specifically: discharge power, electrode gap and duration of exposure have on producing chemical and microstructural changes in the polymer surface region have been investigated. The approach taken involves the application of an orthogonal array experimental design and statistical analysis methodology. The various data sets obtained from these analyses have been used to develop an equation in which induced changes in the surface properties of the DBD modified PMMA films are expressed in terms of the effectiveness of the various processing parameters in producing them.In general, the results obtained clearly indicate that DBD plasma processing is an effective method for the controlled surface modification of PMMA. Relatively short exposures to the atmospheric pressure discharge produces a significant amount of oxygen incorporation at the surface as indicted by a pronounced reduction in water contact angle. Analysis of the role of each of the operating parameters concerned shows that they do indeed have selective effectiveness for inducing resultant surface modification. Duration of exposure to the DBD plasma, expressed here as the number of treatment cycles at a given speed of specimen transit through the electrode gap, was found to play a major role in decreasing the surface wettability of PMMA. Conversely, the magnitude of the discharge power was not a significant parameter in this regard. In contrast, the value of the applied power played the dominant role in achieving the observed enrichment of the surface oxygen abundance, as measured by XPS, with the duration of exposure to the discharge playing a secondary role in this case.The nature and scale of the induced surface changes that originate from the various processing conditions employed have been further considered to determine if an interrelationship exists between them. Non-parametric data analysis indicates that no significant correlation exists between the observed changes in measured polymer wettability and the attendant surface oxygen enrichment. This result suggests that the increase in surface wettability caused by DBD processing, as manifested in a reduced contact angle, is not merely attributable to changes in the surface chemistry. As such, it is postulated that changes in the surface microstructure may also contribute to this change in surface wettability.     

Uniformity analysis of dielectric barrier discharge (DBD) processed polyethylene terephthalate (PET) surface

A dielectric barrier discharge (DBD) plasma, operating in air at atmospheric pressure, has been used to induce changes in the surface properties of polyethylene terephthalate (PET) films. The effects that the key DBD operating parameters: discharge power, processing speed, processing duration, and electrode configurations, have on producing wettability changes in the PET surface region have been investigated. The approach taken involves the application of an Taguchi experimental design and robust analysis methodology. The various data sets obtained from these analyses have been used to studies the effect of the operating parameters on the surface uniformity and efficiency of the said treatment.In general, the results obtained indicate that DBD plasma processing is an effective method for the controlled surface modification of PET. Relatively short exposures to the atmospheric pressure discharge produces significant wettability changes at the polymer film surface, as indicted by pronounced reductions in the water contact angle measured. It was observed that the wettability of the resultant surface shows no significant differences in respect to orientation parallel (L-direction) or perpendicular (T-direction) to the electrode long axis. However, there was significant differences between the data obtained from these two orientations. Analysis of the role of each of the operating parameters concerned shows that they have a selective effectiveness with respect to resultant surface modification in terms of uniformity of modification and wettability. The number of treatment cycles and the electrode configuration used were found to have the most significant effects on the homogeneity of the resultant PET surface changes in L- and T-orientation, respectively. On the other hand, the applied power showed no significant role in this regard. The number of treatment cycles was found to be the dominant factor (at significance level of 0.05) in respect of water contact angle changes at the processed PET surface in both orientations. The driven metal electrodes (stainless steel or aluminium) were apparently superior to the driven dielectric electrode (ceramic or quartz) configurations. The grounded electrode in each case was a silicon rubber-covered aluminium plate (see later). The nature and scale of the surface changes that originate from the various processing conditions employed have been considered so as to determine the optimum treatment conditions in respect of processing outcomes, properties and any orientation dependence. Thus, it was revealed that higher processing speeds and longer processing durations are key for uniformity along the electrode axial orientation, while lower processing speeds and short exposure durations are key considerations, in the corresponding perpendicular orientation. In general, longer processing durations (low processing speeds and a high number of treatment cycles) and higher plasma powers induced greater changes in the surface wettability of the PET, as demonstrated by the observed water contact angles. This behaviour is taken to indicate that different combinations of DBD operating parameters and electrodes produce discharge conditions that can result in different plasma chemical processes in respect of uniformity, treatment efficiency and orientation dependence.     

交流和纳秒脉冲Ar/H2O介质阻挡放电聚丙烯材料表面亲水改性对比研究

为了提高等离子体对聚合物材料表面处理的应用效果,优化亲水处理的条件,研究了交流和纳秒脉冲氩气介质阻挡放电（DBD）中添加适量H₂O,对聚丙烯（PP）亲水改性的处理效果。利用电学和光学诊断方法,系统地对比了交流DBD和纳秒脉冲DBD的放电特性,结果表明,纳秒电源驱动DBD具有更高的放电瞬时功率,更好的放电均匀性和更高的能量效率。通过测量不同水蒸气含量下DBD的OH发射光谱强度,确定了PP材料亲水性处理中H₂O添加的最优含量。利用交流和纳秒脉冲电源驱动DBD分别对PP材料进行亲水改性的处理,测量了不同条件下改性处理后的表面水接触角,并利用原子力显微镜（AFM）和傅里叶红外光谱（FTIR）分别对处理前后PP材料的表面物理形貌和表面化学成分进行分析。结果发现,经DBD处理后PP材料的水接触角明显降低,表面粗糙度明显增大,表面的亲水性含氧基团,羟基（?OH）和羰基（C=O）的数量大幅增加。相比交流电源,纳秒脉冲DBD处理的改性效果更好,其处理后的材料表面水接触角,比交流DBD处理的低5°左右,表面粗糙度也有所提升。而水蒸气的加入可使PP材料的表面水接触角进一步减小4°左右,表面粗糙度明显提升。研究结果为优化DBD聚合物材料表面改性实验条件及处理的效果提供了重要的参考依据。     

The effect of discharge power density on polyethylene terephthalate film surface modification by dielectric barrier discharge in atmospheric air

Polyethylene terephthalate (PET) films are modified using non-equilibrium plasma generated by DBD in atmospheric air, and the effects of discharge power density on the surface modification are studied. It is found that increasing discharge power density can induce more effective treatment of PET films, because this leads to a faster decrease in water contact angle and a faster increase in surface energy due to more creation of polar groups and more obvious etching occurring on the PET surface. So the treatment time needed to achieve the same level of surface treatment can be reduced by increasing the discharge power density.     

Surface treatment of aramid fiber by air dielectric barrier discharge plasma at atmospheric pressure

Aramid fiber samples are treated by air dielectric barrier discharge (DBD) plasma at atmospheric pressure; the plasma treatment time is investigated as the major parameter. The effects of this treatment on the fiber surface physical and chemical properties are studied by using surface characterization techniques. Scanning electron microscopy (SEM) is performed to determine the surface morphology changes, X-ray photoelectron spectroscopy (XPS) is analyzed to reveal the surface chemical composition variations and dynamic contact angle analysis (DCAA) is used to examine the changes of the fiber surface wettability. In addition, the wetting behavior of a kind of thermoplastic resin, poly(phthalazinone ether sulfone ketone) (PPESK), on aramid fiber surface is also observed by SEM photos. The study shows that there seems to be an optimum treatment condition for surface modification of aramid fiber by the air DBD plasma. In this paper, after the 12 s, 27.6 W/cm³ plasma treatment the aramid fiber surface roughness is significantly improved, some new oxygen-containing groups such as C-O, CO and OC-O are generated on the fiber surface and the fiber surface wettability is greatly enhanced, which results in the better wetting behavior of PPESK resin on the plasma-treated aramid fiber.     

Effects of air dielectric barrier discharge plasma treatment time on surface properties of PBO fiber

In this paper, the effects of air dielectric barrier discharge (DBD) plasma treatment time on surface properties of poly(p-phenylene benzobisoxazole) (PBO) fiber were investigated. The surface characteristics of PBO fiber before and after the plasma treatments were analyzed by dynamic contact angle (DCA) analysis, scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). DCA measurements indicated that the surface wettability of PBO fiber was improved significantly by increasing the fiber surface free energy via air DBD plasma treatments. The results were confirmed by the improvement of adhesion of a kind of thermoplastic resin to PBO fiber which was observed by SEM, showing that more resin was adhering evenly to the fiber surface. AFM measurement revealed that the surface topography of PBO fiber became more complicated and the surface roughness was greatly enhanced after the plasma treatments, and XPS analysis showed that some new polar groups (e.g. OCO) were introduced on plasma treated PBO fiber surface. The results of this study also showed that the surface properties of PBO fiber changed with the elongation of plasma treatment time.     

Surface oxidation of a Melinex 800 PET polymer material modified by an atmospheric dielectric barrier discharge studied using X-ray photoelectron spectroscopy and contact angle measurement

Surface properties of a Melinex 800 PET polymer material modified by an atmospheric-pressure air dielectric barrier discharge (DBD) have been studied using X-ray photoelectron microscopy (XPS) and contact angle measurement. The results show that the material surface treated by the DBD was modified significantly in chemical composition, with the highly oxidised carbon species increasing as the surface processing proceeds. The surface hydrophilicity was dramatically improved after the treatment, with the surface contact angle reduced from 81.8° for the as-supplied sample to lower than 50° after treatment. Post-treatment recovery effect is found after the treated samples were stored in air for a long period of time, with the ultimate contact angles, as measured, being stabilised in the range 58-69° after the storage, varying with the DBD-treatment power density. A great amount of the C-O type bonding formed during the DBD treatment was found to be converted into the CO type during post-treatment storage. A possible mechanism for this bond conversion has been suggested.     

Surface modifications of ITO electrodes for polymer light-emitting devices

Surface modifications were performed on the indium tin oxide (ITO) substrates for polymer light-emitting devices, using the different treatment methods including solvent cleaning, hydrochloric acid treatment and oxygen plasma. The influence of modifications on the surface properties of ITO electrodes were investigated by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle, and four-point probe. The surface energies of the ITO substrates were also calculated from the measured contact angles. Experimental results demonstrate that the surface properties of the ITO substrates strongly depend on the modification methods, and oxygen plasma more effectively improves the ITO surface properties compared with the other treatments. Furthermore, the polymer light-emitting electrochemical cells (LECs) with the differently treated ITO substrates as device electrodes were fabricated and characterized. It is observed that the surface modifications on ITO electrodes have a certain degree of influence upon the injection current, luminance and efficiency, but hardly upon the turn-on voltages of current injection and light emission which are close to the measured energy gap of electroluminescent polymer. Oxygen plasma treatment on the ITO electrode yields the better performance of the LECs, due to the improvement of interface formation and electrical contact of the ITO electrode with the polymer blend in the LECs.     

Characterization of a non-thermal plasma torch in streamer mode and its effect on polyvinyl chloride and silicone rubber surfaces

In this study, a non-thermal plasma torch in steamer mode was characterized to apply for surface modification in ambient air. The plasma source is a central rod-ring configuration based on DBD operation. Mixture of Ar/air gases was passed through the hollow Copper rod. A home-built high voltage generator at 18.8 kHz was employed to ignite the plasma. Electrical features of plasma torch were studied and different regions of plasma were examined using optical emission spectroscopy to explore the reactive species that result in efficient treatment. The surfaces of polyvinyl chloride (PVC) and silicone rubber (SIR) films were treated by the cold plasma torch. Contact angle measurement shows the improvement of surface hydrophilicity and wettability. Analysis revealed that the surface energy of the films increases indicating their activation after plasma treatment. This process is attributed to increasing the polar component of the surface energy.     

Geometrical optimization of a surface DBD powered by a nanosecond pulsed high voltage

In this study, surface Dielectric Barrier Discharge (DBD) actuators powered by nanosecond pulsed high voltage are investigated. The goal is to experimentally characterize the surface DBD actuators in terms of electrical and geometrical parameters.The actuators are made of two conducting electrodes separated by a thin dielectric (Kapton films) and arranged asymmetrically. The active electrode is connected to a pulsed high voltage power supply (voltage up to ±10 kV, rise and fall times of 50 ns and pulse width of 250 ns) and the second electrode is grounded.The experimental results show that the energy per pulse (normalized by the length of the active electrode) is smaller when one increases the inter-electrode spacing between 1 and 3 mm, the thickness of the dielectric barrier between 120 and 360 μm or the length of the electrodes between 10 and 50 cm, for both applied voltage polarities.Optical characterization of the plasma layer for different electrode gaps has been investigated by using an ICCD camera. Results indicate that the plasma produced by positive and negative rising voltage propagates in a streamer-like regime with numerous and well-distributed channels, for any electrode gap distance. However, the positive and negative falling voltage produces similar discharges only for large electrode gaps. In this case, the plasma layer starts from a corona spot in contact with the active electrode and expands in the direction of the grounded electrode in a plume shape.     

Functionalization of PET and PA6.6 woven fabrics

In the present work as received woven fabrics of polyethylene terephthalate (PET) and polyamide 6.6 (PA6.6) were exposed to a continuous dielectric barrier discharge (DBD), in air at atmospheric pressure, at selected discharge power values and conveyor speeds. The chemical modification of the fabric surface was studied by contact angle analysis, attenuated total reflection (ATR)-FTIR spectroscopy and X-ray photoelectron spectroscopy (XPS). The results confirmed that the treatment changed the fabric surface chemistry, increasing its wettability by polar liquids and its oxygen content. Contact angle results showed different behaviour of the two polymer fabrics toward ageing effects; while PET showed a contact angle increase along the subsequent days of treatment, the PA6.6 fabric maintained its hydrophilicity even 15 days after treatment. The surface morphology analysed by scanning electron microscopy (SEM), did not show any significant difference before and after treatment.     

Effect of dielectric barrier discharge on semiconductor Si electrode surface

Electrode materials and shapes affected the discharge modes. Meanwhile, the discharge has influence upon electrode surface. In order to study the effect of discharge on semiconductor electrode, the experiments were carried out using single crystal Si wafer as high voltage electrode of atmospheric pressure dielectric barrier discharge in air. The effects of dielectric barrier discharge on Si electrode surface are analyzed by means of field emission scanning electron microscope (FESEM) and X-ray photoelectron spectroscopy (XPS). The results show that surface roughness and oxidation increase with discharge time, while surface nitridation is not observed on Si electrode surface. It is different from Cu electrode. The difference is due to different chemical reactions between electrode surface and air plasma but could also be ascribed to the different analysis techniques used.     

纳秒脉冲放电对聚对苯二甲酸乙二酯憎水改性

基于自主研制的ns脉冲电源(上升沿约70ns,脉宽约100ns)激励介质阻挡放电产生大气压低温等离子体,在CF4气氛下对聚对苯二甲酸乙二酯(PET)表面进行了憎水改性处理,测量了改性前后的薄膜表面的水接触角,给出了CF4气流量、放电电压、处理时间和CF4比例等参数对改性效果的影响规律。结果表明,大气压ns脉冲DBD表面处理能够实现PET材料的憎水性,改性后的PET表面水接触角由66°提高到最大100°。     

The research on the interfacial compatibility of polypropylene composite filled with surface treated carbon fiber

Dielectric barrier discharges (DBD) in ambient air are used on carbon fiber to improve the fiber surface activity. Carbon fibers with length of 75 μm are placed into the plasma configuration. The interaction between modified carbon fibers and polypropylene (PP) was studied by three-point bending (TPB) test. The chemical changes induced by the treatments on carbon fiber surface are examined using X-ray photoelectron spectroscopy (XPS). XPS results reveal that the carbon fiber modified with the DBD at atmospheric pressure show a significant increase in oxygen and nitrogen concentration. These results demonstrate that the surface of the carbon fiber is more active and hydrophilic after plasma treatments using a DBD operating in ambient air.     

等离子体介质阻挡放电氟化改性环氧树脂的时效性

等离子体对材料的改性效果随放置时间会有所减弱,即表现出一定的时效性,限制了等离子体改性技术的进一步发展。为了探究等离子体介质阻挡放电（DBD）氟化改性环氧树脂的时效性,利用等离子体介质阻挡放电实现了环氧树脂表面氟化改性,并利用扫描电镜（SEM）、表面轮廓仪、X射线光电子能谱分析（XPS）、接触角测试仪、高阻计和闪络电压、表面电位测试系统对改性前和改性后放置在25 ℃老化箱中0～30 d的环氧树脂表面进行了物理形貌和化学组分的表征以及电气性能的测试。测试结果表明,DBD氟化改性实现了氟元素在环氧树脂表面接枝,这使得环氧树脂表面能降低,表面电阻率减小,陷阱能级变浅,从而加快了表面电位衰减速度,进而提升了沿面闪络电压。同时,等离子体DBD氟化改性环氧树脂表现出一定的时效性,放置30 d后,氟元素含量减少,表面能增大,表面电位衰减速度略有减慢,闪络电压也有所下降,但仍高于未处理的试样。     

Surface wettability of atmospheric dielectric barrier discharge processed Armos fibers

Wettability of Armos fibers has been investigated after exposed to dielectric barrier discharge (DBD) plasma, which was performed at atmospheric pressure in air while varying the sample treatment time between 9 and 27 s. Contact angles and surface free energy of the original and plasma-treated fibers were measured with dynamic contact angle analysis (DCAA) to reveal the correlation between the fiber wettability and the surface treatment, including surface composition and topography modifications, which were evaluated by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. It was found by XPS analysis that the O/C atomic ratio on Armos fiber surface can be increased from 0.134 to 0.248 after the 18 s exposure to the plasma and many polar functional groups were proved to be incorporated into the surface, which aided good wetting. In addition, AFM observations revealed the changes of fiber surface microstructure, showing significant enhancement of the surface roughness after the treatment, which could also bring the fiber better wettability. What's more, the impacts of fiber surface treatment on its tensile properties were characterized by single fiber tensile strength (SFTS) testing. Results showed that Armos fibers exhibited only slight reductions in their tensile strengths with the great enhancement in fiber surface free energy.     

同轴介质阻挡放电发生器介质层等效电容和负载特性研究

大气压介质阻挡放电(DBD)可以在常压下产生非平衡等离子体,已经成为热点研究领域.通过脉冲或交变电源激发放电,研究电源输出特性、电源与放电发生器负载间的匹配和外界条件对放电的影响对于理解放电现象和提高放电效率具有重要意义.本文采用Lissajous图形法,分别研究了驱动电压、气流速率等因素影响同轴DBD发生器介质层等效电容及负载幅频特性的规律.结果表明,气流速率和驱动电压等外界条件影响DBD发生器的负载特性:介质层等效电容随气流速率增大而减小,随驱动电压增大而增大;幅频特性曲线均表现出RLC回路谐振现象,谐振频率随气流速率增大而增大,随驱动电压增大而减小.通过对比发现,介质层等效电容随频率的变化曲线与幅频特性曲线具有一致的特征,介质层等效电容是影响电路谐振频率动态变化的主要因素.提出了一种有关介质层等效电容的形成机制.