Nanoparticles and Nanowires
Fabrication of nanoparticles of the desired shape and physical properties is a task of great importance for modern electronics, sensors, nanodevices, catalysis, and so forth. One of the approaches for fabricating nanoparticles is based on templating single molecules. We metallize single flexible synthetic polyelectrolyte molecules and prepare structures resembling a 1-D sequence (50-1000 nm in length) of metallic clusters of 2-5 nm in diameter deposited on a solid substrate. The length of the wires is proportional to the contour length of the underlying PE macromolecules. This opens the possibility of regulating the size of nanowires by the molecular weight of the PE. One of the advantages of using synthetic PE is the diverse possibilities of synthetic polymer chemistry for fabricating macromolecules of dedicated size and structure. It would be possible to construct one-molecule devices via metallization of macromolecules of the appropriate architecture.
We use a magnetic field for the fabrication of wire-like structures which are made by linking Fe3O4 superparamagnetic nanoparticles (SPN) with polyelectrolyte molecules. These wires are structures in which the SPN particles are linked permanently and they conserve their shape in spite of thermal motion in the fluid. Further, upon deposition onto solid substrates in the presence of an external magnetic field, they form parallel patterns which remain attached to the substrate with lithography-like stubbornness. Thus, they are immune to washings and changes in the direction of the applied magnetic field. It should be noted that these aligned nanowires constitute an anisotropic system. Magnetization hysteresis on these aligned wires was measured, and it was found that the coercive fields show differences when the magnetic field during the measurement was parallel and perpendicular to the patterns, respectively.
Figure 1. Magnetic Nanowires. [Sheparovych, R.; Sahoo, Y.; Motornov, M.; Wang, S.; Luo, H.; Prasad, P. N.; Sokolov, I.; Minko, S. Polyelectrolyte stabilized nanowires from Fe3O4 nanoparticles via magnetic field induced self-assembly. Chemistry of Materials 2006, 18(3), 591-593. Details]
The magnetic nanowires can be manipulated in an external magnetic field. They can also be used as building blocks for the fabrication of hierarchical two-dimensional (2-D) and three-dimensional (3-D) structures.
- Fabrication of random copolymer, block-copolymer and polymeric supramolecular objects based on polyelectrolyte molecules;
- Mineralization of single PE molecules and fabrication of nanoparticles of different shapes;
- Fabrication of super-paramagnetic nanowires/nanofibers;
- Manipulation with nano-object and positioning nanoparticles;
- Fabrication of nano-devices.
Figure 2. Nanowires based on single molecules. Preparation.
Figure 3. Nanowires and nanoparticles of different shapes based on single molecules.AFM Visualization.
Group co-operates with:
- Prof. C. Tsitsilianis, University of Patras, Greece
- Dr. W. Jaeger, Fraunhofer Institut für polymerforschung, Golm, Germany
- Prof. R. Jérôme, University of Liege, Belgium
- Prof. J. Rabe, Humboldt-Universität zu Berlin, Germany
- Leibniz Institute of Polymer Research Dresden, Germany