Received: 9 January 2018 | Revised: 20 February 2018 | Accepted: 24 March 2018 DOI: 10.1002/ppap.201800007 FULL PAPER Role of adsorbed water on PEEK surfaces prior to - and after - atmospheric plasma activation David Gravis 1 | Fabienne Poncin-Epaillard 2 | Jean-François Coulon 1 1 ECAM RENNES - Louis de Broglie, Campus de Ker Lann, CS 29 128, 35091 Rennes Cedex 09, France 2 Le Mans Université - CNRS no 6283, Institut des Molécules et Matériaux du Mans - Département Polymères, Colloïdes et Interfaces, Avenue Olivier Messiaen, 72085 Le Mans, France Correspondence Jean-François Coulon, ECAM RENNES - Louis de Broglie, Campus de Ker Lann, CS 29 128, 35091 Rennes Cedex 09, France. Email: jean-francois.coulon@ecam- rennes.fr Poly-ether-ether-ketone (PEEK) surfaces have been treated by atmospheric pressure plasma to increase their surface free energies - and hence, their adhesion potential towards metallic coatings as assessed by pull-off test. Firstly, we show that adsorbed water on the polymer surface prior to plasma treatment acts as a shielding barrier against activation of the surface. This shielding effect is annealed by either a second plasma scan or by drying the surface before activation. Secondly, the relative humidity rate seems to be the main aging parameter on plasma-treated surfaces. Our study reveals that high values of surface energies, and thus adhesion potential, can be as- sured and maintained for months by storing the material in a dry atmosphere before and after treatment. KEYWORDS adhesion, ageng, atmospheric pressure glow discharges (APGD), poly-ether-ether-ketone (PEEK) 1 | INTRODUCTION Polymers present low densities, making them good candidates to replace metallic structures to reduce energy consumption in automotive and aero-space industry. On one hand, their relative low mechanical properties are mostly addressed by fibre reinforced composites or technical polymers such as poly-ether-sulfone, poly- ether-imide or poly-ether-ether-ketone (PEEK). On the other hand, their poor surface free energy (γ) leading to insufficient practical adhesion when coated need surface treatment. To prepare their surface for required adhesion, polymer and organic matrix composite surfaces usually undergo several chemical and/or physical treatments. Lately however, for environmental considerations and safety operating conditions, dry-phase processes are spread to replace usual industrial methods while ensuring adhesion properties. Among all the dry-phase processes, plasma treatments have long been developed to enhance polymer or composite wettability. [1,2] Depending on the plasma parameters and the gas composition, it is possible to finely tune the surface properties which range from superhydrophobic [3] to super- hydrophilic. [4] For several industrial applications, atmo- spheric pressure plasma can be a sufficient and effective process to promote high surface free energy [5–7] and adhesion [8–10] as this technology can easily be automatized is flexible, fast and does not require vacuum technologies. Plasma Process Polym. 2018;e1800007. www.plasma-polymers.com © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim | 1 of 8 https://doi.org/10.1002/ppap.201800007