Argon plasma irradiation of polypropylene P. Slepic ˇka a, * , A. Vasina a , Z. Kolská b , T. Luxbacher c , P. Malinsky ´ d , A. Macková d , V. Švorc ˇík a a Department of Solid State Engineering, Institute of Chemical Technology, 16628 Prague, Czech Republic b J.E. Purkyne ˇ University, Department of Chemistry, 40096 Ústí Nad Labem, Czech Republic c Anton Paar GmbH, 8054 Graz, Austria d Nuclear Physics Institute of Academy of Sciences of the Czech Republic, 25068 Rez Near Prague, Czech Republic article info Article history: Available online 25 February 2010 Keywords: Polypropylene Plasma treatment RBS XPS Zeta potential abstract Polypropylene samples were exposed to argon plasma discharge and the changes of the PP surface prop- erties were studied by different methods. Surface wettability was derived from contact angle measured by standard goniometry and chemical structure of the plasma modified PP was studied using X-ray pho- toelectron spectroscopy (XPS) and by Rutherford backscattering spectroscopy (RBS), surface morphology and roughness of samples using AFM. Zeta potential of pristine and modified PP was determined with the SurPASS. The presence of incorporated oxygen in the PP surface layer, about 60 nm thick, was observed in RBS spectra. Oxygen concentration is a decreasing function of the depth. With progressing aging time the oxygen concentration on the PP surface decreases. Plasma treatment results in a rapid decrease of the contact angle, which increases again with increasing aging time. In XPS measurement the oxygen con- taining structures, created by the plasma treatment, were found on the very surface of the modified PP and the zeta potential being changed too. The significant difference in zeta potential between pristine and plasma treated PP clearly indicates that the plasma treatment leads to a more hydrophilic PP surface. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction Polymer based materials have been applied successfully in sev- eral fields as adhesives, biomaterials, protective coatings, micro- electronic components, automotive industry and in other thin- film technologies [1,2]. Owing to the consumer and technological qualities, polypropylene (PP) has very wide spectrum of applica- tion and takes the second place after polyethylene on world release – 20.5%. Polypropylene is applied for manufacture gas and water pressure head pipes, structures, sheets, film, furniture, technical products, the goods of cultural and community purpose. In general, special surface properties with regard to chemical composition, hydrophilicity, roughness, crystallinity, conductivity, lubricity and crosslinking density are required for successful applications. Sur- face modification techniques which can transform polymers into highly valuable finished products have became an important part of the plastic technologies [3]. Plasma treatment of polymers, including corona discharges, is now widely used industrial technique to modify surfaces of many different materials (metals, semiconductors, polymers, and ceram- ics). Polymers are often modified using rare gas (He, Ne, and Ar) or reactive gas (O 2 and F 2 ) plasma. Surface modification of polymers with low-pressure plasma has gained great scientific and industrial importance and it is often used to improve adhesion of coatings, wettability, printability, bio-compatibility and other surface re- lated properties of polymers [4–7]. In this work, we studied surface properties of pristine and plas- ma treated PP with the main aim to understand surface chemistry and wettability of PP after the plasma exposure. Rutherford back scattering (RBS), X-ray photoelectron spectroscopy (XPS) were used for the characterization of the chemical structure of the mod- ified PP and AFM for study of surface morphology and roughness of samples. The zeta potential and contact angle determination were used as methods for characterization of polymer surface. 2. Experimental Polypropylene (PP, supplied by Visteon–Autopal, CR) in the form of 1 mm thick foils was used for the present experiments. The samples were modified in diode plasma discharge on Balzers SCD 050 device for 0–240 s using Ar + plasma (gas purity was 99.997%). The reaction chamber was evacuated to the pressure of 2 Pa and the working pressure during the plasma discharge was 10 Pa. The discharge powers were 3.1 and 8.3 W and the treatment was accomplished at room temperature. Contact angle characterizing the surface wettability, was mea- sured at six positions with distilled water at room temperature using surface energy evaluation system. The aging studies at labo- ratory conditions were performed on samples by measuring the 0168-583X/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2010.02.012 * Corresponding author. Tel.: +420 220 445 159. E-mail address: petr.slepicka@vscht.cz (P. Slepic ˇka). Nuclear Instruments and Methods in Physics Research B 268 (2010) 2111–2114 Contents lists available at ScienceDirect Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb