| As it is very serious in energy sources tension, environmental protection and greenhouse effect, worldwide attentions have been focused on low-temperature plasma technique because it is energy-saving and environment friendly. Though the low pressure glow discharge can produce low-temperature plasma, it is not suitable for continued automatic processing in industry because it needs the vacuum equipment and specific gases. In order to solve this problem, the atmospheric pressure plasma sources are developed rapidly. Among these plasma sources, the atmospheric pressure dielectric barrier discharge (DBD) becomes an investigative hotspot because it can achieve large volume low-temperature plasma in ambient air and has wide industrial applications.Characteristics of material surfaces are correlative with friction, abrasion, oxidation cauterization, wetting and adhesion etc. The surface properties of resistance to wear, wettability and adhesion can be improved by surface treatment. Thus, the material surface modification becomes front research field of material science.In recent years, the atmospheric pressure air DBD plasma surface modification becomes a hotspot in academia and industry. Despite some significative fruits have been gained by the previous researchers, there are many deficiencies in existence, for example, (1) the influence of DBD on electrode surface has not been investigated. It is disadvantageous for electrode selection and optimization. (2) the effects of DBD on glass surface tiny region have not been investigated, and the middle frequency power supply DBD has not been used to make hydrophobic glass. This is disadvantageous for using DBD plasma modification technology to produce new-style glass. (3) the orthogonal experiment has not been used to study the effects of power supply parameters and electrode parameters on polypropylene surface properties, such as wettability and roughness, etc. It is impossible to design a better discharge system for material surface modification. (4) the neural networks technology has not been used for modeling material surface modification by using DBD. It is impossible to simply predict the results of surface modification in DBD plasma and causes the test cost higher. Thus, these questions solving not only can realize the parameter optimization of the atmospheric pressure DBD system, but also can modify material surface effectively. It can save energy sources and reduce processing cost. Moreover, it is possible to make novel glass with different characteristics.Herein, the paper investigates the influence of DBD plasma on electrode surface. Glass and polymer surface modification and the influencing factors are also analyzed. Moreover, the parameters optimization and neural networks modeling are discussed. Orthogonal and uniform experimental design, statistics analysis and artificial intelligence are applied to run the experiments. The paper also tests the specimens by the contact angle meter, AFM (atomic force microscope), SEM (scanning electron microscope), EDS (energy dispersive spectroscopy) and XPS (X-ray photoelectron spectroscopy). The contents of the results investigated are listed in detail as follows.1. An atmospheric pressure air DBD system is developed and used to study the influence of DBD plasma on the surface properties of copper and single-crystal silicon electrode. These provide a theoretical basis for electrode optimization and power supply design. The results show that discharge system can realize the steady discharge. Air DBD plasma changed the microstructure, chemical compositions and wettability of the electrode surface by etching or sputtering, oxidation and nitriding. After plasma treatment, surface roughness increases, oxygen and nitrogen are introduced into material surface, and the former contents is higher than that of the latter. Moreover, the oxidation of silicon electrode is enhanced by blowing nitrogen to it. The wettability of electrode surface is also improved after plasma treatment. These show that electrode is eroded by atmospheric pressure DBD, and its life will be reduced.2. The paper investigates the effects of atmospheric pressure DBD on glass surface. The filamentary DBD plasma treatment not only changes glass surface microstructure in discharge tiny region but also alters its chemical compositions. The middle-frequency power supply is used in plasma pretreatment and hydrophobic coating preparation using dimethyl silicon oil as water repellent. The results indicate that surface activation (expressing by contact angle reduction) and hydrophobicity are increased with discharge power and treatment time increasing within the experimental ranges. The highest water contact angle is 105°. Surface roughness of glass increases by AFM observation. The experimental results also show that it is possible to make hydrophobic glass by using middle frequency power supply DBD. This study provides a new way to make hydrophobic glass in industry.3. In this paper, the middle frequency power supply is used to analyze the influence of air DBD power supply parameters and electrode parameters on polypropylene surface properties. Meanwhile, the paper also studies the effects of the combination of discharge power, treatment time and discharge gap on contact angle, surface oxygen content and the ration between oxygen and carbon using orthogonal experiment. And the regressive equations with 90% confidence interval are obtained according to the experimental results. Some samples in different treatment time or in different parameters combination are tested by XPS. The testing results show that C-O, C-OH, C=O, O-C-O, O-C=O, COOH, O-CO-O and R-NHx, R-CONH2, NHCOOH, -C=N containing functional groups are introduced into PP surface after air DBD treatment. A plasma dose optimization value of 1.5 kJ is obtained by analyzing the relation between plasma dose and contact angle decline at 16 kHz and 1.5mm air gap using aluminium-stainless steel parallel plate electrodes. PP powder degradation occurrs because the molecular weight and melting point decreases after DBD treatment. Finally, the comparison of different material surface modifications has been done at the same discharge conditions. The results show that the designed DBD discharge system can modify the polymers surface effectively, and the nature of polymers has some influence on surface modification. As the discharge parameters can be controlled easily, the topology, chemical compositions and wettability of the polymers' surface can be controlled, too. These studies establish a basis for creating a surface modification model of the atmospheric pressure DBD plasma.4. The paper also establishes the neural networks model about the relationship of the air DBD discharge parameters against glass surface hydrophobicity, polymers hydrophilicity by using uniform experimental design and artificial intelligence technique. The testing data are used to test the obtained optimal neural networks models of glass, polypropylene, polyvinyl chloride, polystyrene and polyethylene terephthalate. The results indicate that the absolute errors and the root mean square errors are less than 1°, the relative errors are less than 3% in all the models. These show that the models built have good predictive accuracy. And the research provides a new method for predicting the results of DBD plasma surface modification in an industrial location and is very important for industrial applications.
|
PDF Full Text Request