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Dielectric barrier discharge (DBD) is proved to be an effective method for surface treatment of polymers over the past 20 years and is now widely used in the fields of surface modification. In this paper, surface treatment of polyethylene terephthalate (PET) films for improving the hydrophilicity using DBD excited by unipolar nanosecond pulses is presented. Two typical discharges exhibiting homogeneous and filamentary modes are obtained under certain experimental conditions, and then, they are used to modify the surface of PET films. The microstructure and properties of the film surface before and after treatment are characterized with water contact angle measurement, scanning electron microscope, atomic force microscope, and X-ray photoelectron spectroscope. The results show that, with the treatment power density of 192 and 158 mW/cm2 in filamentary and homogeneous modes, respectively, surface morphology and property after treatment are significantly changed, and the physical etching and introduction of oxygen-containing polar functional groups account for the decease of surface contact angle and the increase of surface roughness. Compared with the filamentary DBD treatment, the homogeneous DBD (HDBD) is more effective in surface treatment, such as lower contact angle, higher roughness, and more oxygencontaining function groups after treatment. It is attributed to the fact that the HDBD can achieve a uniform treatment and canmake the physical and chemical interaction much sufficient. [ABSTRACT FROM AUTHOR]

Repetitive pulsed power is becoming an important area of high-power technology. Dielectric failure data concerning electrical insulation play a basic role, but breakdown has been inadequately studied for the repetitive nanosecond-pulse conditions. This paper is concerned with the breakdown characteristics of tip-plane gas gaps under repetitive burst conditions at variant repetition rates (rep-rates) and diverse gap distances. The relationship among applied voltage, breakdown time lag, number of applied pulses to breakdown, repetitive pulse stress time, and rep-rates is presented. The experimental results presented show that breakdown polarity dependence is not distinct. The data also indicate that significant concentrations of excited particles and residual charges would be formed during the consecutive nanosecond pulses and would present a memory effect that affects the development of gas breakdown. In addition, the detachment of negative ions, cathode collision of positive ions, and deexcitation of metastable species can provide the source of avalanche-initiating electrons. [ABSTRACT FROM AUTHOR]

This paper illustrates images of dielectric-barrier discharge (DBD) excitated by repetitive unipolar nanosecond pulses in atmospheric air. Different images are obtained for three barrier dielectrics and various gap lengths. Discharge images show that the nanosecond-pulse DBD observed with the eye is a diffuse glowlike mode when air gap is 2 mm; clear filamentary discharge is seen with the eye in the case of air gap of 8 mm. The results show that gap length and dielectrics are the important factors influencing the transition from diffusive to filamentary discharges. [ABSTRACT FROM AUTHOR]