The effect of glow discharge plasma on the surface properties of Poly (ethylene terephthalate) (PET) film K. Navaneetha Pandiyaraj a , V. Selvarajan a, ⁎ , R.R. Deshmukh b , Mosto Bousmina c a Plasma Physics Laboratory, Department of Physics, Bharathiar University, Coimbatore-641 046, India b Department of Applied Physics, Institute of Chemical Technology, University of Mumbai, Matunga, Mumbai 400 019, India c Canada Research Chair on Polymer Physics and Nanomaterials, Department of Chemical Engineering (CREPEC), Laval University, Sainte-Foy, Canada PQ G1K 7P4 Received 25 September 2007; accepted in revised form 14 March 2008 Available online 25 March 2008 Abstract In the present work, Poly (ethylene terephthalate) films have been exposed to glow discharge air plasma to improve their surface properties for technical applications. Surface energy values have been estimated using contact angle value for different exposure times and different test liquids. Surface composition and morphology of the films were analyzed by XPS and AFM. Crystallinity of the plasma treated samples were studied by XRD analysis. The improvement in adhesive strength was studied by measuring T-peel strength and lap shear strength tests. It was found that the plasma treatment modified the surfaces both in chemical composition and morphology. Change of chemical composition made the polymer surfaces to be highly hydrophilic, which mainly depends on the increase in oxygen-containing groups. The AFM and XRD observation showed that the surface roughness and crystallinity of the PET film increased due to plasma treatment. © 2008 Elsevier B.V. All rights reserved. PACS: 81.65.Cf; 52.50.Dg; 52.77.-j Keywords: PET; Glow discharge plasma; Surface energy; XPS; AFM; Adhesion 1. Introduction Nowadays polymers find wide applications in modern industry. However, bonding and finishing of many polymers present a problem due to the low hydrophilicity of their surfaces. It affects the wettability, printability, biocompatibility and adhe- sion. For this reason polymer films need some additional treat- ment to raise the surface activity, for better wettability and adhesion properties [1–5].There are different methods to modify the surface properties of the polymer films such as graft poly- merization, corona discharge and laser irradiation. Recently, research on the use of plasma treatments has grown in interest [6,7] since they are environmentally efficient. The glow discharge is a dry process and allows better uniformity in the surface. Depending on the gas used for plasma generation and the general conditions, it is possible to activate a polymeric surface by insert- ing active species, surface etching, cross linking process or in combination of the processes. The use of low pressure conditions allows the plasma treatment at low or moderate temperatures; in this way, the aggressiveness of the plasma treatment is consid- erably reduced and consequently degradation is reduced. It is possible to generate a glow discharge plasma by either direct or RF current. At industrial level, RF excitation is preferred for surface modification [1–3]. The different species present in plasma induce the formation of free radicals in the polymeric chain and in this way it is possible to insert or interact certain function groups on the polymer surface which will enhance the surface properties of the polymeric films. In the present work a DC glow discharge air plasma was applied to improve the intrinsic low surface properties of a PET film. The hydrophilicity of the PET film was characterized by measuring contact angle as a function of exposure time. In addition, the plasma treated samples have been subjected to an ageing process to determine the durability of the plasma treatment. The surface morphology and crystallinity of the modified PET films were analyzed using Available online at www.sciencedirect.com Surface & Coatings Technology 202 (2008) 4218 – 4226 www.elsevier.com/locate/surfcoat ⁎ Corresponding author. Tel.: +91 422 24226576. E-mail address: vselvrjn47@rediffmail.com (V. Selvarajan). 0257-8972/$ - see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2008.03.015