In the field of electronic organic materials, conjugated polymers (CPs) have attracted much attention in recent years. It has been well-established that
performances of thin-film devices based on π-conjugated polymers, such as light-emitting diodes, field-effect transistors and photovoltaic cells, are strongly dependent on the organisation of the polymer molecules and their interactions with other constituents in multicomponent devices. The use of CPs in integrated circuits, solar cells, light-emitting diodes or sensors often requires their covalent fixation and patterning on various surfaces. CPs can be grafted to functionalized surfaces by (electro)chemical cross-linking; however, it is difficult to control a structural order within the cross-linked films. The attachment of CP chains to substrates by their end-points to form polymer brushes would be an interesting alternative, and could possibly be crucial for many devices requiring charge injection and charge transport processes.
The main aim of this work, which was the synthesis of covalently grafted conjugated polymer brushes on solid substrates using a "grafting from" approach, was successfully performed.
During the course of this work, the process of surface-initiated polycondensation was investigated. The newly developed method to selectively graft conjugated polymers from different substrates such as Si-wafers, quartz slides or modificated nanoparticles allowed us to produce different architectures which were earlier possible to prepare only non-conductive polymers. Exposure of the substrate with an activated surface layer into the monomer solution produced polymer brushes in a very economical way. Since only monomer was consumed for grafting from the surface.
The grafting process was extensively investigated by different methods, and the thickness of the obtained poly(fluorene) films was elucidated by Null-ellipsometry and confirmed by the AFM scratch-test. Preliminary characteristics of the device, based on PS(Br)-core poly(octylfluorene)-shell nanoparticles, showed satisfactory results (such as turn-on voltage and electroluminescence in a blue region). They could be improved by replacement of the insulating PS(Br)-core of nanoparticles with other substances (semiconductive, etc.). There is still plenty of room for further
development and improvement of the synthesis of poly(fluorene)-based polymer brushes.
The polymer structures developed in this work can be utilized as an active layer in lab-on-chip devices. Alkyl groups in the 9th position of the poly(fluorene) monomer unit can be replaced by tailored receptors to detect specific species including small molecules, metal ions and biomolecules due to enhanced sensitivity through sensory signal amplification. Post-polymerization modifications may lead to highly water-swellable conjugated polyelectrolyte brushes. Also, polymerization of initially optically active fluorene-monomers may be the crucial step to the generation of a light source devices with a large degree of circularly polarized electroluminescence. This is of great interest for utilization as backlight for liquid crystalline displays. We believe that the utilization of covalently surface-immobilized conjugated polymers may have a great impact on the development of present-day technological processes.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:25562 |
| Date | 19 April 2011 |
| Creators | Boyko, Kseniya |
| Contributors | Stamm, Manfred, Jordan, Rainer, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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