597 Research Article Received: 14 August 2007 Revised: 2 October 2007 Accepted: 2 October 2007 Published online in Wiley Interscience: 5 March 2008 (www.interscience.com) DOI 10.1002/sia.2619 Comparison between XPS- and FTIR-analysis of plasma-treated polypropylene ﬁlm surfaces R. Morent, a* N. De Geyter, a C. Leys, a L. Gengembre b and E. Payen b Plasma treatment is often used to modify the surface properties of polymer ﬁlms, since it offers numerous advantages over the conventional surface modiﬁcation techniques. In this paper, a polypropylene (PP) ﬁlm is plasma-treated using a dielectric barrier discharge (DBD) operating in air at medium pressure (5.0 kPa). The modiﬁed polymer ﬁlms are characterized using contact angle measurements, XPS-analysis and attenuated total reﬂectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Results show that plasma treatment leads to a remarkable decrease in contact angle owing to the implantation of oxygen-containing functional groups. Using XPS and ATR-FTIR, these oxygen-containing groups can be identiﬁed as C–O, C O and O–C O. In this paper, it is also shown that XPS is well-suited to provide quantitative chemical analysis of the PP ﬁlms, while ATR-FTIR can only give qualitative information. To perform quantitative ATR-FTIR measurements, chemical derivatization will be explored in the near future. Copyright c  2008 John Wiley & Sons, Ltd. Keywords: dielectric barrier discharge; polypropylene; XPS and ATR-FTIR Introduction Polymers like polypropylene (PP) are frequently used as ﬁlms and foils for packaging, protective coatings and sealing applications, because of their superior bulk properties, such as transparency, a high strength-to-weight ratio, good thermal resistance, .... De- spite these excellent characteristics, polymers are often unsuitable to use owing to their low surface-free energies. [1] Therefore, sur- face treatments are usually necessary to improve surface-wetting and adhesion properties. Chemical activation of the surfaces is the most utilized method, [2] however, the ecological requirements force the industry to search for alternative environmentally benign methods. The application of cold plasmas to modify surface properties of polymers is such a rapid and environmentally friendly process. [3] Plasma contains active species, such as electrons, ions, radicals, photons,... which are able to initiate chemical and physical modiﬁcations at the polymer surface. [1,4,5] The advantage of this technique is that plasma treatment only changes the uppermost atomic layers of a material without modifying the bulk properties. Therefore, the modiﬁcation depth of the plasma treatment is only a few nanometers. [3,4] Commonly used techniques to characterize the treatment are contact angle measurements and surface free-energy calculations. [6] For the chemical analysis of the surface modiﬁ- cation, the most used technique is XPS owing to its low analyzing depth. [6] However, XPS measurements are time-consuming. Com- pared to XPS, attenuated total reﬂectance-Fourier transform infrared (ATR-FTIR) spectroscopy is a fast technique, but FTIR spectroscopy is believed to be of no use to characterize surface modiﬁcations at the top nanometer levels because predominately the bulk material is studied. In this paper, a dielectric barrier discharge (DBD) operating in air at medium pressure (5.0 kPa) will be used to modify the surface properties of a PP ﬁlm. A DBD or ‘silent discharge’ can be obtained between 2 electrodes, at least one of which should be covered with a dielectric, when an AC high voltage is applied between the electrodes. [7] The most interesting property of DBDs is that in most gases the breakdown starts at many points, followed by the development of independent current ﬁlaments (named microdischarges). These microdischarges are of nanosecond duration and are uniformly distributed over the dielectric surface. [7] Characterization of the plasma-induced surface changes will be performed using XPS and ATR-FTIR spectroscopy. The results of both techniques will be compared and discussed in detail. Experimental Set Up The schematic conﬁguration of the experimental set up is represented in Fig. 1. The discharge is produced between two circular copper electrodes (diameter = 4 cm), placed within a cylindrical enclosure. Both electrodes are covered with a ceramic Al 2 O 3 plate (thickness = 0.7 mm, area = 5 cm × 5 cm) and the distance between the two ceramic plates is 2 mm. The upper electrode is connected to an AC power source (frequency = 10 kHz), while the lower electrode is connected to earth through a resistor of 100 . The discharge power is calculated using a Lissajous ﬁgure [8] and is kept constant at 1.4 W. After placing a PP ﬁlm (Goodfellow-UK) with an area of 4 cm × 4 cm and a thickness of 0.075 mm on the lower ceramic plate, the discharge chamber is pumped down to 5.0 kPa using a ∗ Correspondence to: R. Morent, Department of Applied Physics, Research Unit Plasma Technology (RUPT), Faculty of Engineering, Ghent University, Jozef Plateaustraat 22, B-9000 Ghent, Belgium. E-mail: Rino.Morent@ugent.be a Department of Applied Physics, Research Unit Plasma Technology (RUPT), Faculty of Engineering, Ghent University, Jozef Plateaustraat 22, B-9000 Ghent, Belgium b Unit´ e de Catalyse et Chimie du Solide, UMR CNRS 8181, Universit´ e des Sciences et Technologies de Lille, Bˆ at. C3, Cit´ e Scientiﬁque, 59655 Villeneuve d’Ascq, France Surf. Interface Anal. 2008; 40: 597–600 Copyright c  2008 John Wiley & Sons, Ltd.