Modification of Glass Surface by Atmospheric Pressure Plasma

A Diffuse Coplanar Surface Barrier Discharge (DCSBS) operating in air at atmospheric pressure has been used to induce changes in the surface properties of glass. The contact angles of water drop on the surface of glass, which were measured by drop shape analysis, decreased markably with plasma treatment for 1 s. With the increasing of the plasma treatment time, the contact angles of the samples treated by air plasma decreased to lower values, and by using the dynamic treatment mode, the values of contact angles decreased rapidly below unmeasurable limit. We also investigated the durability of the treatment. Introduction Material processing techniques such as cleaning of material surfaces, removing organic or films, and modifying polymer surface properties are one of the well established plasma application areas. In particular, the glow discharge plasma was known to be the appropriate discharge mode for material processing because of its high density and flux of active species for chemical reactions on material surfaces. As a consequence, various low-pressure plasma sources which easily produce glow-like plasma have been widely used in the industry. However, plasma sources operating at atmospheric pressure have recently received increased attention since they need no expensive high vacuum equipment and have in-line processing capability [J.R.Roth, 2001]. Simply way to generate nonequilibrium plasma at atmospheric pressure is the use of dielectric barrier discharge (DBD). DBD occurs in arrangements where at least one dielectric is positioned in the gas space in between conducting electrodes. Quite unique type of the DBD generator, so called Diffuse Coplanar Surface Barrier Discharge (DCSBD), can produce very thin layer of non-equilibrium plasma with high power density (up to 100 W/cm) and, practically, in any working gas [M. Šimor et al., 2002]. Comparing to other surface DBD schemes (as e.g. the one invented by Masuda et al. [S. Masuda et al., 1988]), major advantage of the DCSBD is that surface micro-discharges are in no contact with metallic electrodes, thus ensuring long lifetime of the system. The aim of this work is to increase the surface energy of glass surface by DCSBD. Freshly cleaned glass surfaces have a high surface energy and are well wettable. They, however, have a tendency to adsorb organic contamination from the ambient environment. Adsorbed organic contaminant molecules, generally less than the full monolayer coverage, of the order of nm thickness, will generate heterogeneous wettability. This may lead to non-uniform glass coatings, in particular if deposited from liquid media as in the case of widely used sol-gel coatings, silane coupling agent coatings, electroless metal plating, as well as in jetting fluid dispensing technology that is gaining popularity in the flat panel display manufacturing [Thomas Ratledge]. Experimental setup DCSBD electrode geometry consists of many parallel stripline electrodes embedded in 96% alumina as schematically shown in Figure 1. Thickness of the ceramic layer between the upper surface and electrodes is ~ 0.4 mm. The discharge was powered by AC (~ 14 kHz, up to 20 kV peak-to-peak) high voltage. Electrical measurements were performed using a digitizing oscilloscope Tektronix TDS 2000 (bandwidth 200 MHz), a Tektronix P6015A (1000:1) high voltage probes and a Pearson Electronic 4100 current probe. The configuration of electrical measurement is also showed in Figure 1. The glass samples (microscopic glass slides 76 mm x 26 mm) were treated in air plasma with the treatment time varying from 1 to 8 s. The distance between sample and ceramics was 0,3 mm, the discharge power was 355 W. WDS'07 Proceedings of Contributed Papers, Part II, 124–128, 2007. ISBN 978-80-7378-024-1 © MATFYZPRESS