 Press Release
Angewandte Chemie International Edition 2008, 47, 4509–4511
doi: 10.1002/anie.200801028 Nr. 21/2008 A Wafer of PolyethyleneUltrathin polyethylene films made of nanocrystalsContact: Stefan Mecking, Universität Konstanz (Germany)
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Crystalline Polymer Ultrathin Films from Mesoscopic Precursors
Layers of plastic, much thinner than a strand of hair—this type of ultrathin
polymer film is of great interest to scientists and engineers.
Applications include protective coatings, for example. A research team
led by Stefan Mecking at the University of Konstanz has now developed a
new method to produce wafer-thin layers. As reported in the journal Angewandte
Chemie, the scientists made their films from individual
prefabricated nanocrystal building blocks.
© Wiley-VCH
The conventional method for the production of ultrathin polymer films (films
with a thickness of less than 0.1 µm) begins with a dilute solution of
the polymer in an organic solvent, which is applied to a surface. In
order to break up the crystalline structure of the solid polymer to get
it into solution in the first place, high temperatures are usually
required. The ordered crystalline layer only forms once the solvent is
removed or cooled.
Mecking and his co-workers have taken a completely different approach that
works at room temperature and without organic solvents. The polymer of
choice was polyethylene (PE), a polymer with a simple chemical structure
and a broad spectrum of technical applications ranging from films and
packaging materials to technical components or implants. PE is
physiologically harmless and environmentally friendly—but has been hard
to produce in ultrathin films.
The catalytic polymerization of ethylene with nickel complexes produces
aqueous dispersions of crystalline polymer particles. These are
individual, separate single crystals consisting of crystalline lamella
of about 25x6 nm surrounded by an amorphous (noncrystalline) layer with
a thickness of 1 nm. Amorphous domains on the surface are a typical
occurrence in polymer crystals. Droplets of this aqueous dispersion are
applied to a glass slide and spun at 2000 revolutions per minute (spin
coating). Excess liquid is spun away, leaving behind a wafer-thin
uniform film with a thickness of 50 nm.
The success of this attractive production technique rests on the amorphous
domains around the single crystals in combination with the tiny size of
the crystals. Although the amorphous domains only comprise a tiny
portion of the volume of the particles, they interact very strongly with
each other, holding the individual particles solidly in the film.
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