One-dimensional nanostructures such as nanowires, nanotubes, and nanorods have a large potential as building blocks for assembling nanodevices. However, their optical and electronic properties are strongly dependent on size and geometry, and so far, a high degree of control over these properties has been lacking.

Now, researchers have developed a new method which addresses this problem, by creating water-soluble organo-silica hybrid nanowires that are readily size controllable [Yuan et al., Nat. Mater. (2008), doi:10.1038/nmat.2232].

To synthesize the hybrid nanowires, Axel H. E. Müller and his team from the Universität Bayreuth, Germany employed cylindrical polymer brushes (CPBs). These are molecular brushes consisting of polymer chains, which are tethered by one end to a central linear polymer chain.

“We constructed CPBs with a monomer that contains a precursor for silica, and used them as templates for our one-dimensional nanostructures,” explains Müller. “By an intramolecular sol-gel process, we successfully synthesized hybrid nanowires with a silsesquioxane (R-SiO1.5) core and a shell made up of oligo(ethylene glycol) methacrylate (OEGMA) units, which are soluble in water and many organic solvents.”

The length and diameter of the rigid wires are tunable by the number of repeat units in both the backbone and the side chains, which can be precisely controlled by anionic and atom transfer radical polymerization, respectively. These are both examples of so-called living polymerization techniques, the hallmark of which is a highly constant rate of chain growth, that results in very similar chain lengths.

“Our approach provides a new route to the controlled fabrication of inorganic or hybrid silica nanostructures by living polymerization techniques,” says Müller. “These nanowires can be employed to generate uniform, rigid inorganic silica nanowires, or to construct lyotropic phases (namely phases that form liquid crystals following the addition of an appropriate solvent).”

Krzysztof Matyjaszewski, from Carnegie Mellon University in Pittsburgh, finds this work impressive, commenting: “This is a beautiful example that shows how living polymerization techniques can be successfully employed to prepare materials with very special architecture.”

The researchers hope to extend their methodology to nanostructures with different shapes, such as tubes, spheres, and lamellae. They also have plans to functionalize the hybrid nanowires with magnetic, fluorescent, and semiconducting properties.