ABSTRACT PLASMA SURFACE MODIFICATION AND CHARACTERIZATION OF PMMA FILMS &Ouml / zgen, &Ouml / zge M.Sc., Department of Polymer Science and Technology Supervisor: Prof. Dr. Nesrin Hasirci Co-supervisor: Prof. Dr. Vasif Hasirci December 2011, 114 pages Surface properties play an essential role for determining the behavior of a material for many applications such as coating, printing, adhesion and prosthesis implanting since the surface is the first part that comes in contact with the environment. Although the bulk properties of some materials are at the desired level, the surface may need to be modified for a better compatibility with its surrounding. Plasma treatment is one generally preferred technique because of its high potential to create various functional groups on the surface of the sample by changing the applied plasma parameters. Some molecules can be successfully immobilized onto these surfaces using these specific chemical functional groups created by plasma. The type of the functional group is important for intended purpose of covalent binding of different molecules on the surface of a material. Present study offers important routes for optimization of the surface functionality of (PMMA) films by changing the plasma parameters. For this purpose, solvent casted polymethylmetacrylate PMMA films were modified by, nitrogen, argon and oxygen plasma by using a radiofrequency (RF) generator / and with various powers (10W, 50W, 100W) for different periods (5min, 15min and 30min). The effects of these plasma parameters (gas type, applied power, plasma time) on hydrophilicity, surface free energy, surface chemistry, and surface topography were investigated. Also, the types of surface free radicals created with oxygen plasma treatment were analysed and the decay of these radicals were examined by Electron Spin Resonance Spectroscopy (ESR). In general, plasma treatment reduced the contact angle of PMMA films where the most hydrophilic surface was obtained for 100W 30 min argon plasma treated sample showing superhydrophilic character with the water contact angle value of ~10&deg / . Surface free energy measurements were carried out according to Geometric Mean, Harmonic Mean, Acid-Base approach and it was found that oxygen, nitrogen and argon plasma treatments increased the surface free energy for all samples by increasing the polar components and introducing functional groups on the surface. X-Ray Photoelectron Spectroscopy (XPS) analysis results revealed that free carbonyl and carbonate groups were formed by oxygen plasma treatment, whereas carboxylic acid and free carbonyl groups were formed after argon plasma treatment, and imine, primary amine, amide and nitrozo groups were formed by nitrogen plasma. Atomic Force Microscopy (AFM) analysis revealed that the roughness of the surface increased considerably from ~2 nm to ~75 nm for the 100W 30 min oxygen plasma treated samples. ESR analysis indicated the presence of peroxy radicals on the surface of the oxygen plasma treated PMMA and the intensity of these radicals increased with increasing plasma power. Decay study of the newly created radicals demonstrated that after 1 month under the atmospheric conditions there were still peroxy radicals on the surface of PMMA. This functionality is important in leading time for further process for binding of different molecules to the surface of the materials for specific purposes. As a result, RF plasma was found to be an effective tool for modification of surface properties of materials with product diversity for intended purposes.

Le procédé par lequel des forces sont transformées en signaux chimiques joue un rôle fondamental dans de nombreux processus biologiques. Ce travail de thèse a permis de mettre au point de nouvelles surfaces fonctionnelles synthétiques permettant de mimer ce comportement. Il s’agit plus précisément de contrôler l’adsorption d’objets biologiques tels que des protéines ou des cellules sur un support élastique modifié par plasma et présentant des récepteurs spécifiques. Ces récepteurs sont masqués par de longues chaînes de poly(éthylèneglycol) (PEG) qui sont également greffées sur la surface. L'étirement de celles-ci permet d'exhiber les sites d’adsorption ou les sites d'adhésion et de rendre ainsi la surface adhérente. Notre méthode est basée sur la polymérisation plasma de l’anhydride maléique. Cette fonctionnalisation permet de greffer à la surface de films silicones des fonctions carboxylique qui servent de points d’ancrage aux chaînes de PEG. Sur le même principe, la biotine ou les peptides d’adhésion (RGD) sont greffés dans un deuxième temps sur ce substrat. Nous montrons, qu’à l’état non étiré, ces ligands ne sont pas accessibles pour leurs récepteurs. Par contre, à l’état étiré, la surface devient spécifiquement adsorbante pour la streptavidine, l’anti-biotine et adhérente pour les cellules. Ces phénomènes sont parfaitement réversibles. / The process by which forces are converted into chemical signals play a fundamental role in many biological processes. This thesis has to develop new functional synthetic surfaces to mimic this behavior. It is more precisely to control the adsorption of biological objects such as proteins or cells on an elastic support modified by plasma and presenting specific receptors. These receptors are masked by long chains of poly (ethylene glycol) (PEG) which are also grafted onto the surface. Stretching allows them to exhibit adsorption sites or adhesion sites and thus make the surface adhesive. Our method is based on the plasma polymerization of maleic anhydride. This functionalization can be grafted to the surface of silicone films carboxylic functions which serve as anchors points for the PEG chains. On the same principle, biotin or adhesion peptides (RGD) have been grafted in a second time on this substrate. We show that the non-stretched state, these ligands are not accessible to their receptors. On the other side, in the stretched state, the surface becomes specifically adsorbent to streptavidin, anti-biotin and also adherent for cells. These phenomena are perfectly reversible.

This diploma thesis builds on my bachelor thesis, which was focused on the application of low-pressure hydrogen plasma and argon-hydrogen plasma on layers of corrosion products. According to results of the experiments, an appropriate temperature for plasma chemical treatment of lead samples was detected. However, the process of corrosion removal through plasma chemical treatment needs to be further optimized to prevent potential damage to the original historical artefacts. Optimization of the treatment process is therefore the main subject of this work’s research. The model samples with artificial corrosion layers with dual composition were prepared. These samples were put to desiccator with sand and organic acid. The samples corroded in environment of acetic acid or formic acid with the aim of creating the corrosion, which would be at least partially simulated with corrosion on the original artefacts. The process of corrosion lasted for eleven months. After that, the samples were dried out under reduced pressure, put to the protecting foil with humid and oxygen absorbers. In contrast with my bachelor thesis where the continuous regime was chosen for the treatment, the pulse regime with three different condition settings is used. Process of experiment was monitored by OES, surface of samples was analyzed by SEM, EDX, XRD methods. Results from experiments with model samples were used for treatment of original artefacts with missing documentation, so their eventual damaging was acceptable.