INSTITUTE OF PHYSICS PUBLISHING PLASMA SOURCES SCIENCE AND TECHNOLOGY Plasma Sources Sci. Technol. 15 (2006) 849–857 doi:10.1088/0963-0252/15/4/031 Using a He + N 2 dielectric barrier discharge for the modification of polymer surface properties G Borcia 1 , A Chiper and I Rusu Plasma Physics Department, A.I. Cuza University, Iasi, Romania E-mail: g.borcia@uaic.ro Received 28 July 2006, in final form 1 September 2006 Published 26 September 2006 Online at stacks.iop.org/PSST/15/849 Abstract In this paper we report on the optimization of an experimental arrangement of DBD type, aiming to work in a He + N 2 environment, applied to the surface treatment of polymers. Here the discharge was systematically investigated on an extended range of the gas mixture composition, using electric parameter measurement and emission spectroscopy. The effects of the He + N 2 -DBD treatment on the surface of a test material are examined, compared with results obtained on the He-DBD treatment. The surface characterization was performed using contact angle measurement, AFM imaging and XPS analysis, so allowing the selection of treatment parameters for reproducible, efficient and stable surface modification. Introduction Atmospheric pressure, non-thermal plasmas possess unique features that have led to a number of important applications. Electrons of sufficient energy colliding with the background gas can result in low levels of dissociation, excitation and ionization without an appreciable increase in the gas enthalpy. This is the realm of non-thermal plasmas in which the electron temperature can exceed the temperature of the heavy particles (atoms, molecules, ions) by orders of magnitude. Because the ions and the neutrals remain relatively cold, these plasmas do not cause thermal damage to surfaces they may come in contact with. This characteristic provides the possibility of using these plasmas for low-temperature plasma chemistry and for treatment of heat-sensitive materials including polymers and biological tissues [1]. In this respect, dielectric barrier discharges (DBD) are convenient plasma sources for the generation of non-thermal plasmas at atmospheric pressure, gaining much interest as processing techniques for the activation or modification of polymer surfaces, as they offer the possibility of inducing significant surface chemical modifications on a material exposed to the discharge at or near atmospheric pressure, thus avoiding the high engineering costs usually associated with vacuum-based plasmas [2, 3]. 1 Author to whom any correspondence should be addressed. Usually the DBD plasma consists of many tiny microdischarges (or filaments) of nanosecond or microsecond duration. Under special operation conditions, particularly in certain gases or gas mixtures, glow homogeneous discharges can be obtained in a DBD configuration [4]. The homogeneity of the DBD is very desirable for industrial applications, especially for surface treatment processes [3, 5–9]. Helium could be considered the most convenient gas when working at atmospheric pressure, while it allows stabilizing homogeneous glow discharges at atmospheric pressure much easier compared with other gases, at lower sustaining voltages and inter- electrode gaps as high as a few centimetres [10]. Helium is also very suitable for use in polymer surface treatments, with its low degradation effect and high properties of crosslinking and functionalization onto the surface [11, 12]. The controlled surface modification of polymers by incorporation or generation of specific functional groups could be thus achieved using various gaseous mixtures of the type He+X, where X is a reactive species. The discharge parameters and the treatment conditions should then be selected to allow obtaining uniform, stable and reproducible surface properties, under conditions simulating ‘real’ continuous processing. Recognizing the above, here a DBD at atmospheric pressure is optimized to work in a He + N 2 environment aiming to improve the surface properties of polymer films. The nitrogen is selected due to the interest in creation of nitrogen- related functional groups onto polymer surfaces aimed to be 0963-0252/06/040849+09$30.00 © 2006 IOP Publishing Ltd Printed in the UK 849