This paper investigates mechanisms of the surface charge dissipation of silicone rubber (SiR) after dielectric barrier discharge (DBD) plasma treatments in an open air. Electrical and physicochemical properties of the untreated and plasma treated samples were evaluated by surface and volume conductivity, surface potential decay (SPD) measurements, Fourier transform infrared (FT-IR), and water contact angle tests. Results show that the surface conductivity of the plasma treated samples evidently increases with the treatment time. The samples with a longer DBD plasma treatment time enhance the SPD rate after the positive and negative corona charging. However, an abnormal surface potential variation is observed at the beginning of the SPD after the negative corona charging. It is found that the top-bottom surface plasma treatment can further accelerate the SPD of the samples compared with the untreated and single surface plasma treated samples. The physicochemical analysis shows that the concentration of polar groups is increased after the plasma treatment, and the water contact angle is consistently declined with the increase of the plasma treatment time. The calculated trap distribution illustrates that the hole trap energy and the electron trap density of the sample are decreased after the plasma treatments. This investigation attributes the measured SPD of the untreated sample and single surface treated samples to the electrical conduction along the sample surface, but the SPD of the top-bottom surfaces plasma treated samples is enhanced by the charge neutralization and transportation through the material bulk as well as the sample top surface conduction.

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This paper presents an investigation on DC flashover voltage of silicone rubber (SiR) improved by dielectric barrier discharge (DBD) plasma treatments under ambient atmospheric pressure air. DC surface conductivity, surface potential decay (SPD), DC surface flashover voltage, partial discharge magnitude, Fourier transform infrared (FT-IR) spectrograms, and surface water contact angles are measured to analyze the influence of plasma treatment on the SiR. It is found that the speed of SPD increase consistently with the plasma modification time. The tendency of flashover voltage is increasing at first and then decreasing with the increased time of the plasma treatment. The magnitude and number of partial discharge pulses increase apparently with the increased plasma treatment time. Physicochemical measurements indicate that more amount of polar groups appear on surface after the DBD plasma modification, whereas the surface water contact angles decline continuously with the increased plasma modification time. However, the hydrophobicity is recovered after 30 d exposure in the air. It is demonstrated that the SPD is accelerated significantly due to the increased surface conductivities and density of shallow traps. However, the reduction of flashover voltage after longer time of the plasma treatment is attributed to the increased mobility of charge carriers on the sample surface.

Understanding of the mechanisms underlying plasma-polymer surface treatments using atmospheric pressure plasmas can guide their industrial applications.. To this end, a novel vacuum ultraviolet photodissociation reactive species supply (VUV PRS) method, which can quantitatively supply the desired type of reactive species to polymer surfaces, was developed in our previous study. In this study, the innovative approach is used to quantitatively study the effects of O radicals on polypropylene (PP) surface treatment. Specifically, water contact angle (WCA), attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, and atomic force microscope (AFM) are used to characterize the surface modification. The results show that the surface treatment is dominated by O radicals under the present experimental conditions. The surface modification rate, characterized by the WCA decline rate, is linearly correlated with the concentration of O radicals, that is (surface modification rate) = (8.1 ± 0.4)[Os] + (0.13 ± 0.02) degrees/s, where [Os] indicates the density of O radicals at PP surface (in ppm). The ATR-FTIR spectra shows that –OH and C=O functional groups are introduced onto the PP surface after the treatment, which results in a decrease in the WCA of the surface. Atomic force microscopy (AFM) analysis shows that the surface morphology of the treated PP remains almost unchanged. Low molecular weight oxidized materials (LMWOMs) on PP surface are generated when the O radical dose that arrives at the PP surface exceeds a certain threshold. More than 60% of the oxygen-containing functional groups exist as LMWOMs when the WCA saturates. The results presented in this paper indicate that the VUV PRS method has the potential to drive the understanding of plasma-polymer surface interactions at the atomic and molecular levels. Moreover, the measured roles of the O radicals on the polymer surface at atmospheric pressure can guide the industrial application of atmospheric pressure plasma treatment.

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The plasmonic properties of asymmetric Au / SiO 2/ Au sandwiched cross-shape nanobars are investigated theoretically using the discrete dipole approximation (DDA) method. Two localized surface plasmon resonances are observed in the extinction spectra, which perform extreme sensitivity to the length and width of the nanobar and can be tuned easily throughout visible and into near-infrared spectral regions. The local electric fields around the nanobar are calculated and a pure electromagnetic Raman enhancement factor of about 106 can be achieved. In addition, compared to a monolayer gold nanobar, it exhibits more "hot spots" and stronger localized electric field enhancements. This plasmonic substrate provides potential applications in surface enhanced Raman scattering (SERS) and nonlinear optical devices.