Applied Surface Science 288 (2014) 251–257 Contents lists available at ScienceDirect Applied Surface Science j ourna l ho me page: www.elsevier.com/locate/apsusc Rapid surface treatment of polyamide 12 by microwave plasma jet J. Hnilica, L. Potoˇ cˇ náková, M. Stupavská, V. Kudrle ∗ Department of Physical Electronics, Masaryk University, Kotlᡠrská 2, CZ-61137 Brno, Czech Republic a r t i c l e i n f o Article history: Received 13 March 2013 Received in revised form 3 October 2013 Accepted 4 October 2013 Available online 12 October 2013 Keywords: Polyamide Plasma treatment Contact angle AFM XPS a b s t r a c t Polyamide 12 (PA 12) films were plasma treated using a microwave surface wave jet at atmospheric pressure. The parameters were the treatment time and the gas composition (argon or argon with admix- tures). Moreover, the influence of power modulation was studied. It was found that significant change in wettability is achieved very rapidly, after only 25 ms of treatment. Plasma-induced surface changes are discussed using AFM, ATR-FTIR and XPS results. It is concluded that the increase in wettability is caused by both chemical and morphological changes. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Microwave discharges at the atmospheric pressure, especially surface wave sustained discharges, have flexible operating con- ditions resulting in a wide range of processing applications, such as thin film deposition, gas decontamination, plasma sterilisation, light sources and lasers, particle production, material processing, etc. [1–4]. Polyamide 12 (PA 12) is a thermoplastic material that is rigid, hard wearing, and resistant to oils, solvents, and alkalis. A known problem with polyamide and many other polymers are their poor hydrophilic properties, which affect their wettability, printability, adhesion, etc. In polyamide it is related to the availability of the hydrogen bonds among the molecules with amide groups. This can be overcome by increasing the surface energy by an appro- priate surface modification method. One of the promising methods is plasma surface modification [5,6]. Plasma treatment is widely used nowadays as an effective tool for physical and chemical modification of polymer surfaces, while not affecting the bulk material [7–11]. Under the bombardment of active species (charged particles, excited particles, radicals, UV radiation, etc.) generated by the plasma, the polymer surface can be modified either by removing surface contamination [12–14], introducing new chemical functional groups [15–17] or deposit- ing a thin coating [18,19]. Plasma surface modifications are often used to improve surface adhesion, hydrophilicity and roughness as required for the enhanced wetting, dyeing and printing [20–22]. ∗ Corresponding author. Tel.: +42 0549495433. E-mail address: kudrle@sci.muni.cz (V. Kudrle). Traditionally, most plasma systems operated at low pressure, requiring rather expensive and complicated vacuum equipment [23]. This can be avoided by using dielectric barrier discharge (DBD) systems or plasma jets working at the atmospheric pres- sure [5,6,10]. Using the microwave discharges can be advantageous over DC, low frequency or RF plasmas as they generally have higher power density, which can positively influence both homogeneous and heterogeneous plasma–chemical reactions. The net effect could then be a potentially faster plasma treatment. This paper aims to find and to report the treatment conditions (gas admixture, treatment time, continuous wave versus ampli- tude modulation), for which the plasma jet treatment would induce sufficient hydrophilisation of the polyamide 12 surface without damaging it. The interest in such enhanced hydrophilisation came from an application – polyamide sheet gluing. With this application in mind we also tried to achieve shorter treatment time compared to the established techniques. Important issue that was considered as well, was the ageing effect of treated samples. The modification of polyamide surface by plasma treatment was investigated by means of contact angle measurement, atomic force microscopy (AFM), attenuated total reflectance Fourier transform infra-red spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). 2. Experimental set-up 2.1. Plasma system The surface treatment was carried out using an atmospheric pressure microwave electrode-less jet – surfatron (commercial 0169-4332/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2013.10.016