PUB - Publikationen an der Universität Bielefeld

The fabrication of fully cross-linked and chemically patterned (FCCP) monolayers has been developed in this work. FCCP monolayers can be further chemically functionalized. Chemically defined surface structures are of great practical interest, as they may be used in many technologies such as molecular electronics, biosensors, etc. Crosslinking enhances mechanical stability of FCCP monolayers, so they can be released from the substrate by dissolution from their substrate or by scission of the anchor group-substrate bonds. This results in an extremely flat, two dimensionally extended layer which is better known as a nanosheet. A patterned nanosheet can be transferred either onto a solid substrate such as silicone oxide or silicone nitrate, or to a TEM grid with openings of up to tens of micrometers. Fabrication of freestanding homogenous and patterned polymer brushes is of great interest for both scientific studies and industrial applications. These materials may find a broad range of applications in many surface-based technologies. We developed a new strategy in preparing freestanding homogenous and patterned polymer brushes: a combination of electron beam chemical lithography (EBCL), 2D carbon-based nanosheet and self-initiated photografting-photopolymerization (SIPGP) to obtain well defined freestanding homogenous and micro- and nanostructured polymer brushes. This new approach offers several advantages: 1. Nanosheets are thermally and mechanically extremely stable. This will make them a good candidate for polymerization at elevated temperatures as well as in intense UV light. 2. EBCL as a patterning tool offers stability, flexibility, selectivity, high throughput and superior resolution. 3. SIPGP offers a simple procedure for preparing polymer brushes. As no SAM modification step is necessary for the preparation of surface-bonded initiator, a tedious, tricky step in the preparation of polymer brushes can be avoided and the polymerization process becomes simplified. With this new approach, a soft and stimuli responsive 10-300 nm thick polymer brush layer is grafted, forming so-called "polymer carpets". These polymer carpets exhibit remarkable properties (optical, wetting) combining extreme thinness, mechanical stability, robustness, flexibility and an unprecedented chemical sensitivity. Precise control of the membrane thickness as well as its mechanical and chemical properties can be obtained by varying the monomer type and polymerization time. Moreover, polymer carpet layers buckle and unbuckle reversibly by applying an external (chemical) stimulus. This unprecedented reversible and fast conformational change is visible by the naked eye and can be applied in the development of new and advanced sensors, displays and micromechanical systems. Furthermore, freestanding patterned polymer brushes were also successfully fabricated. By combining patterned FCCP nanosheets with subsequent SIPGP, high pattern resolution of freestanding polymer layer, as well as almost-defect free on large area of polymer layer, can be achieved. Because of their excellent properties, both freestanding homogenous and patterned polymer brushes are very promising for many applications. Freestanding polymer layers will respond faster due to the isolation from the underlying support. This makes them excellent candidates for applications in pressure-based sensors, micro- and nanoactuators, cell adhesion studies and development of microelectromechanical systems (MEMS).