## 1 Introduction  
Polymeric web materials are ubiquitous in today's society, with demand set to increase in areas as diverse as plastic electronics and biodegradable or compostable packaging. Key to determining the properties and performance of a polymer are its surface functionalities, such as barrier properties (i.e., permeability to water and oxygen), printability, coefficient of friction, hydrophobic or hydrophilic properties, and optical properties. Surface functionalities can be modified through vacuum processing, i.e., film deposition or surface modification. This, though, imposes both handling and vacuum equipment costs for high throughput applications. Thus, in many cases, the preferred solution would be to perform the processing at atmospheric pressure. Atmospheric pressure plasma technology can offer major industrial, economic and environmental advantages over conventional processing methods. Application areas include functionalizing thermally sensitive materials, deposition of thin films (e.g., SiO\({}_{2}\)), surface decontamination, and sterilization of medical devices [1]. Surface modification of polyolefins, such as polypropylene, is a particularly important commercial process, because their adhesion and wettability to hydrophilic substances is very low. This causes problems such as low printability, delamination and poor bonding to coatings and adhesives. Up to 70% of polyolefins produced require a surface modification technique before they can be processed further [2]. Numerous designs/technologies exist for atmospheric pressure plasma surface modification of polyolefins, including plasma jets [3], corona treatments [4], atmospheric pressure glow discharges [5]and dielectric barrier discharges (DBD) [6]. It is now generally accepted that these treatments result in an increase in surface energy by introducing polar groups on the surface, thus improving their adhesion and wetting properties [4]. However, the combination of treatment uniformity, scaleability, throughput, and reproducibility make DBDs the process of choice in many large-scale commercial applications. The DBD is an established technology used in many applications, such as exhaust gas purification [7], ozone production [8], medical sterilisation [9; 10], plasma display panels [11], plasma actuators as flow controllers [12], water purification [13; 14; 15] and deposition of thin films (plasma enhanced chemical vapour deposition) [16; 17; 18]. DBD systems consist of a pair of parallel plate electrodes that are held a few mms apart, but can be several metres in length. Thus, they are also ideally suited to the treatment of polymeric web [6; 19; 20]. In an industrial DBD system for web treatment, the upper electrode is a cooled roller or drum, which transports the film through the plasma. A flexible dielectric, such as silicon rubber, covers the roller and the polymer film is in contact with the dielectric as it passes around the drum and travels through the process zone formed between the two electrodes. The width and the diameter of the roller are typically of the order of a few metres. The speed of the film during treatment ranges up to a few hundred meters per minute. The necessary power to sustain the discharge reaches tens of kilowatts. The lower electrode is in the shape of an arc, which matches the radius of curvature of the drum in order that the two electrodes are coaxial and parallel to each other. In addition, the lower electrode is corrugated perpendicular to the machine direction. As a consequence, the plasma is only ignited where the distance between the two electrodes is minimal and is, thus, highly concentrated on the top of the corrugated electrode.