重复频率纳秒脉冲介质阻挡放电对聚对苯二甲酸乙二酯表面改性

介绍了0.1 MPa下的纳秒脉冲介质阻挡放电(DBD)对聚对苯二甲酸乙二酯(PET)材料表面进行的亲水性改善。分别采用均匀和丝状放电模式对PET表面改性处理,并采用水接触角测量、原子力显微镜观察、X射线光电子能谱分析对改性材料进行表面分析。实验发现介质阻挡放电处理后PET表面水接触角明显减小,接触角从78°下降到25°,但随处理时间的增加有饱和效应;PET表面粗糙程度增加,亲水性含氧基团被引入,从而改善了材料表面亲水性;纳秒脉冲下的均匀DBD比丝状DBD处理效果更为显著。     

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。     

用于聚四氟乙烯表面处理的重复频率高压脉冲电源

采用自行研制的μs级重复频率高压单极性脉冲电源,应用于聚四氟乙烯(PTFE)膜表面改性,研究脉冲放电等离子体对PTFE薄膜表面改性的作用规律。测量处理前后PTFE薄膜表面的水接触角,结果显示,在特定的脉冲参数及更严格的对比条件下其平均水接触角从112°下降到85°,PTFE薄膜表面亲水性改善效果非常显著。脉冲电源采用脉宽调制控制方式,通过逆变升压及波形整形,得到脉冲电压幅值0~20kV、重复频率0~20kHz、脉宽5~15μs、上升沿500ns~2μs、下降沿大于20μs的单极性脉冲。     

纳秒脉冲空气辉光放电等离子体及应用

采用基于半导体断路开关的纳秒脉冲高压电源,在两个金属电极之间产生放电区间为1 600mm×100 mm×25 mm的常压辉光空气等离子体。等离子体发生器采用负高压针电极阵列与平板阳极结构,针电极的直径为1 mm,长度为20 mm,针电极之间的间隔为20 mm,针电极与平板零电位之间的距离为25mm,在每个负高压针电极末端周围同时形成圆锥形辉光放电,在平板地电极则形成大面积辉光放电。采用电压探针测量了该新型等离子体的放电特性,结果表明:放电脉冲的上升时间为26 ns,最高脉冲输出峰值电压为27 kV;利用该辉光等离子体对幅宽为1 000 mm聚四氟乙烯薄膜进行了表面改性处理,处理后其表面接触角由原来的124°降到69°,亲水性能大为提高。     

氮离子注入对聚四氟乙烯表面电荷积聚和消散特性的影响北大核心CSCD

为了抑制聚四氟乙烯材料表面电荷积聚,采用射频产生氮等离子体对其表面进行等离子体浸没离子注入以改善其表面性能。对注入前后的聚四氟乙烯材料样品进行了X射线光电子能谱分析(XPS)、傅里叶红外光谱测试(FTIR)、水接触角测量、表面电阻率测量以及表面电位衰减测量,并基于等温表面电位衰减理论对其表面陷阱能级和密度分布进行了计算,以分析聚四氟乙烯样品经离子注入处理后其表面成分和物理性能的变化,并研究了这些变化对聚四氟乙烯样品表面电荷积聚和消散特性的影响。结果表明:氮离子注入后,聚四氟乙烯材料表面化学成分的主要变化是自身分子结构的破坏和转化,部分CF2结构转变为CF和CF3结构,导致样品表面陷阱能级变浅;水接触角升至140°左右,比未处理样品上升了约27°,表面电阻率降至3×10^15Ω,比未处理样品下降了两个数量级;表面电晕放电1 min后,经氮离子注入处理的聚四氟乙烯材料表面积聚电荷量减少,消散速度加快,这是因为表面陷阱能级变浅有利于表面电荷脱陷,同时表面电阻率降低也促进了表面电荷沿面传导的消散过程,聚四氟乙烯样品表面陷阱能级分布曲线也证实了这一论点。     

大气压介质阻挡放电的光谱研究

使用水电极介质阻挡放电装置,分别在大气压空气和氦气中实现了稳定的高气压放电。通过水电极观察两种气体的放电,发现大气压空气中放电为空间随机分布的微放电丝,等离子体是不均匀的,而在氦气中放电没有微放电丝,空间分布比较均匀。比较而言,这种均匀放电产生的等离子体具有更广泛的工业应用前景。对两种气体中放电的电流波形进行了比较,发现空气中放电的电流脉冲在时间上是随机出现的而氦气中放电的电流脉冲在时间上具有周期性,并且空气中放电脉冲宽度约为几十ns而氦气中放电的电流持续时间较长,脉冲宽度大约为1μs。文章还对两种气体中介质阻挡放电发射光谱进行了研究,结果表明大气压氦气中均匀放电的N+₂(B2Σ+_u→X2Σ+_g)谱线391.4nm很强而在大气压空气放电中此光谱线很弱。这些研究结果对高气压条件下均匀放电的实现和大气压辉光放电的工业应用具有重要意义。     

大气压空气中重复频率纳秒脉冲气体放电模式研究

利用上升沿100ns、脉宽150ns的单级磁压缩纳秒脉冲电源,通过电压电流测量和放电图像拍摄实验,研究了大气压空气中极不均匀电场结构重复频率纳秒脉冲气体放电的放电模式。结果表明纳秒脉冲气体放电存在三种典型的放电模式:电晕放电、弥散放电和火花放电。施加的脉冲电压幅值对放电模式影响显著,随着电压幅值的增加,放电依次经历电晕、弥散和火花放电。固定电压幅值时,放电可能同时存在两种模式。重复频率加强了放电强度,弥散放电的激发电压随重复频率的增加变化不大,但火花放电的激发电压随着重复频率的增加而降低。因此降低重复频率有利于在较大电压范围获得大气压空气弥散放电。     

空气中纳秒脉冲介质阻挡放电高速摄影

使用上升沿40 ns、脉宽70 ns的重复频率单极性纳秒脉冲电源,采用双水电极结构产生大气压空气中介质阻挡放电。测量了纳秒脉冲下介质阻挡电压和电流,并获得长曝光时间和ns级曝光时间的放电特性,采用曝光时间为2 ns的高速摄影拍摄放电发展过程。结果表明:大气压空气中,水电极结构纳秒脉冲介质阻挡放电能够产生稳定均匀的放电等离子体,且存在二次放电。高速摄影对放电发展过程的拍摄结果表明:放电首先由电极中部开始发展,径向扩展至整个电极范围。     

High speed imaging of nanosecond-pulse dielectric barrier discharge in atmospheric air

使用上升沿40 ns、脉宽70 ns的重复频率单极性纳秒脉冲电源,采用双水电极结构产生大气压空气中介质阻挡放电.测量了纳秒脉冲下介质阻挡电压和电流,并获得长曝光时间和ns级曝光时间的放电特性,采用曝光时间为2 ns的高速摄影拍摄放电发展过程.结果表明:大气压空气中,水电极结构纳秒脉冲介质阻挡放电能够产生稳定均匀的放电等离子体,且存在二次放电.高速摄影对放电发展过程的拍摄结果表明:放电首先由电极中部开始发展,径向扩展至整个电极范围.     

分段表面放电击穿特性研究

 给出了采用表面滑闪放电诱导长距离(42cm)、线性等离子体通道大电流放电的分段表面放电辐射源的结构,依据传输线模型计算了分段表面放电辐射源放电通道电场分布,分析了触发脉冲和比表面电容对击穿特性的影响,实现了各段总的放电分散时间小于100ns。     

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.     

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.     

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.     

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.     

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.     

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.     

Fluorocarbon nano-coating of polyester fabrics by atmospheric air plasma with aerosol

A fluorocarbon coating was deposited on polyester (PET) woven fabric using pulse discharge plasma treatment by injecting a fluoropolymer directly into the plasma dielectric barrier discharge. The objective of the treatment was to improve the hydrophobic properties as well as the repellent behaviour of the polyester fabric. Plasma treatment conditions were optimised to obtain optimal hydrophobic properties which were evaluated using water contact angle measurement as well as spray-test method at the polyester fabric surface. The study showed that adhesion of the fluoropolymer to the woven PET was greatly enhanced by the air plasma treatment. X-ray photoemission spectroscopy (XPS) analyses revealed chemical surface modifications occurring after the plasma treatments.     

含氮氟化类金刚石(FN-DLC)薄膜的研究：(Ⅲ)疏水性能分析

不同沉积条件下，在单晶硅基底上沉积了含氮氟化类金刚石(FN-DLC)薄膜，用静滴接触角/表面张力测量仪测量了水与FN-DLC膜表面的接触角.用X射线光电子能谱、Raman光谱和傅里叶变换吸收红外光谱(FTIR)分析了薄膜的组分和结构.用原子力显微镜观测了薄膜的表面形貌.结果表明，FN-DLC薄膜疏水性能主要取决于薄膜表面的化学结构、薄膜表面极化强度的强弱、以及薄膜的表面粗糙度的大小.sp³/sp²的比值减小，CF₂基团含量增加，薄膜粗糙度增加，接触角增大；反之，则接触角减小.在工艺上，沉积温度和功率的减小，气体流量比r(r=CF4/［CF₄+CH₄］)的增加，都会使水的浸润性变差，接触角增大. 关键词： 氟化类金刚石膜 疏水性 接触角