Light plus special building blocks equal a molecular carpet
They decided to do the synthesis in a single crystal, i.e. a crystal with a homogeneous layer lattice. PhD student Patrick Kissel successfully used this to crystallize special monomers in layered hexagonal single crystals. The monomers he generated are photochemically sensitive molecules, for which such an arrangement is energetically optimum. When irradiated with light with a wavelength of 470 nanometers, the monomers polymerized in all the layers of the crystal. To separate the individual layers from one another the researchers boiled the crystal in a suitable solvent. Each layer represents a two-dimensional polymer.
The fact that the team really had succeeded in producing sheet-like polymers with regular structures was shown by special studies in a transmission electron microscope (TEM) carried out by Empa researcher Rolf Erni and Marta Rossell from ETH Zurich (who meanwhile is also working at Empa's Electron Microscopy Center). These two-dimensional polymers are extremely sensitive towards irradiation. It's really tricky to not destroy their structure during the TEM measurements, which made the analyses a real tough nut to crack, says Erni. Diffraction experiments at minus 196oC the condensation point of nitrogen and high-resolution images at a low electron dose allowed the Empa scientists to eventually provide proof that the cross-linked molecules indeed exhibit a regular two-dimensional structure.
Potential application: a molecular sieve
The polymerization method that was developed is so gentle that all the monomer's functional groups are also preserved at defined positions in the polymer. Says Sakamoto, Our synthetically manufactured polymers are not conductive like graphene, but on the other hand we would be able to use them for example to fil
|Contact: Dr. Rolf Erni|
Swiss Federal Laboratories for Materials Science and Technology (EMPA)