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2nd Int. Workshop on Non-equilibrium Processes in Plasmas and Environmental Science IOP Publishing Journal of Physics: Conference Series 162 (2009) 012015 doi:10.1088/1742-6596/162/1/012015

Surface Functionalization of Organic Materials by Weakly Ionized Highly Dissociated Oxygen Plasma
Alenka Vesel1 and Miran Mozetic1
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Jozef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, SloveniaE-mail: alenka.vesel@ijs.si, miran.mozetic@guest.arnes.si
Abstract. A review on surface modification of different polymers by treatment in oxygen plasma is presented. Plasma is created in a high frequency inductively coupled gaseous discharge at the power of about 200 W. In such discharge created in pure oxygen, plasma with the following parameters is obtained: the electron temperature of about50.000 K, the charged particle density around 1x1016 m-3, and the neutral oxygen atom density of the order of 1021m-3. A huge flux of neutral oxygen atoms on the surface of samples exposed to plasma assures for rapid interaction with polymer materials. The modification of surface properties of the following polymers was studied: polyethyleneterephthalate (PET), polyethersulphone (PES),polyphenylenesulfide (PPS), Nylon 6 polyamide (PA6), polytetrafluoroethylene (PTFE), polystyrene (PS), polypropylene (PP) and cellulose (ink-jet paper and textile). The polymer samples were treated for 3 s in oxygen plasma at a pressure of 75 Pa where the O-atom density was the largest at 4x1021 m-3. The appearance of the functional groups on the surface of the samples was monitored by high resolution X-rayphotoelectron spectroscopy (XPS). The results show that oxygen plasma treatment is an effective tool for surface modification. On all polymer surfaces increased concentration of oxygen is detected. The high resolution C1s peaks indicate formation of several new oxygen-containing functional groups. On all polymers groups like C-O, C=O and O=C-O are observed. The concentration of these groupsdepends on the type of polymer. The highest uptake of oxygen by the polymer was found for cellulose and the lowest for polypropylene. The only exception was polymer PTFE where practically no chemical changes were observed after plasma treatment.

1. Introduction 1.1. Surface energy and adhesion Surface properties of materials depend on the properties of bulk materials as well as surface contaminants.The surface energy is largest for metals, followed by ceramics and glasses, and is lowest for non-polar polymers. Even carefully cleaned materials are often covered with very thin films of different impurities such as native oxide films and traces of hydrocarbons that definitely modify the original surface energy of pure materials. The surface energy often determines the adhesion of differentcoatings on the substrates. Apart from the roughness, the surface energy is usually the key parameter that affects the quality of coatings on polymers and polymer matrix composites. Modern industry requires components that are made from materials with desired mechanical, chemical, optical and electrical properties, and are coated with different films often incompatible with the substrates. In suchcases, the surface properties should be modified without modification of the bulk properties.

c 2009 IOP Publishing Ltd

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2nd Int. Workshop on Non-equilibrium Processes in Plasmas and Environmental Science IOP Publishing Journal of Physics: Conference Series 162 (2009) 012015 doi:10.1088/1742-6596/162/1/012015

Several techniques have appeared to reach this goal: they include a variety ofwet chemical treatments, modification by energetic particle beams and application of gaseous plasma. Although atmospheric plasmas are increasingly popular, low pressure plasmas have some advantages. The main advantage of low pressure plasma is spreading over a large volume that assures for rather uniform treatment of three dimensional objects with a complex shape. 1.2. Plasma treatment of...