Nanopatterning of Poly(ethylene terephthalate) by Plasma Etching

16 Ellen Wohlfart Nanopatterning of Poly(ethylene terephthalate) by Plasma Etching Institute of Materials Science, University of Stuttgart and Max Planck Institute for Metals Research, Stuttgart, 2010 179 pages, 84 figures, 12 tables Abstract: Nano and microstructured surfaces found on shark skins, lotus plants, moth eyes or gecko feet can reduce flow resistance, generate self-cleaning surfaces, antireflection layers or reversible adhesion forces. Great interest has developed in transferring the principles of nature to technical applications. Therefore, different patterning techniques have been developed, such as optical, e-beam, or soft lithography, to generate micro and nanostructures on material surfaces. However, all of these techniques have limitations. Most of them require special equipment, are time consuming, expensive or can only structure small areas. In this thesis a simpler, timesaving and less costly patterning procedure is developed which relies on reactive ion etching of polymer surfaces. High aspect ratio nano structures with diameters between 15 and 40 nm and lengths up to 1 μm were fabricated on Poly(ethylene terephthalate). A systematic study of the influence of plasma and polymer parameters was performed to understand and control structure formation during plasma treatment. Commercial and laboratory-made films with different amounts of crystallinity and orientation were plasma treated and subsequently analysed using scanning electron microscopy, weight loss measurements, differential scanning calometry and wide-angle x-ray diffraction. Fibril length could be adjusted by variation of plasma parameters, whereas the polymer microstructure influenced material response to plasma treatment and therefore the resultant surface design. Different etching rates in domains of different order, generated by thermal and mechanical pretreatment, was considered as the mechanism for fibril generation. The nanostructured surfaces exhibited very low adhesion compared to flat analogues and an increasing friction coefficient with increasing surface roughness. By combining plasma treatment with fluorinated coatings, superhydrophobic surfaces with a lotus effect were obtained. Nano and microstructured surfaces found on shark skins, lotus plants, moth eyes or gecko feet can reduce flow resistance, generate self-cleaning surfaces, antireflection layers or reversible adhesion forces. Great interest has developed in transferring the principles of nature to technical applications. Therefore, different patterning techniques have been developed, such as optical, e-beam, or soft lithography, to generate micro and nanostructures on material surfaces. However, all of these techniques have limitations. Most of them require special equipment, are time consuming, expensive or can only structure small areas. In this thesis a simpler, timesaving and less costly patterning procedure is developed which relies on reactive ion etching of polymer surfaces. High aspect ratio nano structures with diameters between 15 and 40 nm and lengths up to 1 μm were fabricated on Poly(ethylene terephthalate). A systematic study of the influence of plasma and polymer parameters was performed to understand and control structure formation during plasma treatment. Commercial and laboratory-made films with different amounts of crystallinity and orientation were plasma treated and subsequently analysed using scanning electron microscopy, weight loss measurements, differential scanning calometry and wide-angle x-ray diffraction. Fibril length could be adjusted by variation of plasma parameters, whereas the polymer microstructure influenced material response to plasma treatment and therefore the resultant surface design. Different etching rates in domains of different order, generated by thermal and mechanical pretreatment, was considered as the mechanism for fibril generation. The nanostructured surfaces exhibited very low adhesion compared to flat analogues and an increasing friction coefficient with increasing surface roughness. By combining plasma treatment with fluorinated coatings, superhydrophobic surfaces with a lotus effect were obtained. Kurzzusammenfassung 17 Ellen Wohlfart Nanopatterning of Poly(ethylene terephthalate) by Plasma Etching Institut für Materialwissenschaft, Universität Stuttgart und Max-Planck-Institut für Metallforschung, Stuttgart, 2010 179 Seiten, 84 Abbildungen, 12 Tabellen Kurzzusammenfassung: Nanound mikrostrukturierte Oberflächen auf der Haifischhaut, der Lotuspflanze, den Mottenaugen oder den Geckofüßen reduzieren den Reibungswiderstand, erzeugen selbstreinigende Oberflächen, entspiegelnde Beschichtungen oder reversible Haftung. Es ist ein großes Interesse entstanden, die Prinzipien der Natur auf technische Anwendungen zu übertragen. Deshalb wurden unterschiedliche Strukturierungsmethoden wie zum Beispiel Lithographieverfahren entwickelt. Allerdings haben alle Techniken Beschränkungen. Sie benötigen eine spezielle Ausrüstung, sind sehr zeitintensiv, teuer oder es können nur kleine Flächen strukturiert werden. In der vorliegenden Arbeit wurde eine einfache Strukturierungsmethode entwickelt, die auf reaktivem Ionenätzen von Polymeroberflächen basiert. Strukturen mit einem hohen Aspektverhältnis, einem Durchmesser zwischen 15 und 40 nm und einer Länge bis zu 1 μm konnten auf Polyethylenterephthalat hergestellt werden. Es wurden systematische Untersuchungen durchgeführt, um den Einfluss der Plasmaund Polymerparameter auf die Strukturentstehung zu verstehen und zu kontrollieren. Dazu wurden Filme mit unterschiedlicher Kristallinität und Orientierung plasmabehandelt und anschließend mit Rasterelektronenmikroskopie, Gewichtsverlustmessungen, Dynamischer Differenzkalorimetrie und Weitwinkel-Röntgenstreuung analysiert. Durch Variation der Plasmaparameter konnte die Säulenlänge eingestellt werden, während die Mikrostruktur des Polymers die erhaltene Oberflächenstruktur bestimmte. Vermutlich sind unterschiedliche Ätzraten in Domänen mit unterschiedlicher Ordnung (entstanden durch thermische und mechanische Vorbehandlungen) verantwortlich für die Entstehung der Nanosäulen. Kombiniert man die Plasmabehandlung mit einer fluorhaltigen Beschichtung, so erhält man superhydrophobe Oberflächen mit Lotuseffekt. Die strukturierten Oberflächen zeigen eine geringe Adhäsion im Vergleich zu glatten Proben und einen steigenden Reibungskoeffizienten mit zunehmender Substratrauigkeit.