Research

Polymers and Nanoparticles

In the field of controlled polymerization at surfaces, we since long have been dedicated to the coating of material surfaces with polymers that perform a variety of functions. By attaching polymer chains to surfaces, we obtain polymer brushes and films and thereby not only modify macroscopic surfaces, but also nanoparticles (NPs), whereby we obtain tailor-made nanocomposites. To control the surface-polymer, we mainly use controlled radical RAFT polymerization, which enables controlled growth and precise attachment of polymer chains at predefined locations. A modular combination of polymer and NPs is thus accessible,

which allows for the design of a multitude of different functional nanostructures. We pioneered the concept of arranging NPs by means of RAFT polymer that is directly grafted to gold NPs (AuNPs) via its thiocarbonylthio-endgroup. Gold surfaces are special in functionalization by RAFT polymers, because the sulfur-containing RAFT groups can form bonds to gold themselves without further conversion. By this building block concept, we were able to arrange two different AuNPs in a planet-satellite structure using star polymers from RAFT polymerization:

In order to expand the flexibility of our nanoengineering toolbox, we explored and used silica nanomaterial as additional platform for nanocomposites. By further optimizing and adapting the rather mature silica chemistry, we were able to fully integrate this material – which often has properties that are complementary to those of noble metals – into our building block strategies. We used silica to coat various NPs in order to adapt the surface properties of metal for polymer and solvent interaction and for providing an optimum surface for surface-initiated polymerization, which we have explored extensively. We were, e.g., able to coat palladium nano-cubes with a mesoporous silica shell, which improved the corresponding catalysis process, we were able to coat magnetite NPs with silica, by which we could reduce disturbing magnetic interaction phenomena,

and we could cover polymer particles that are filled with either gold NPs or magnetic NPs with protecting silica shells.
We also developed a novel strategy to easily form precise ring-shaped arrays of AuNPs by polyethylene glycol-(PEG)-grafted AuNPs, that were attached to silica NP cores via hydrogen bonding in a controlled fashion, forming well-defined core–satellite structures in colloidal solution. The attached gold NPs show unique surface mobility on the silica core surface, which allows for NP rearrangement into a 2D ring pattern surrounding the silica NP template when the core–satellite structures are cast to a planar surface. When etching away the silica core under conditions, in which the polymer shell fixes the satellites to the substrate, highly ordered ring-shaped patterns of AuNPs were formed.