Angewandte Chemie International Edition
© WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
For full article and contact information, see Angew. Chem. Int. Ed. 2003, 42 (7), 778 - 781
Plastics with a Sense of Order
Liquid crystals as templates for the synthesis
of ordered conducting polymers
They always cause a stir at electronics trade shows; electrically conducting plastics are the materials of the future in many areas of microelectronics. Components such as wide organic displays, foil-batteries, or plastic chips will be ready for mass production in the foreseeable future.
The advantages of conducting polymers over other materials for the production of silicon-free electronics are high stability, favorable mechanical properties, and easy processing. However, their electrical conductivity has thus far left a lot to be desired. It suffers because of the structural disorder that usually prevails in plastics. Samuel I. Stupp and James F. Hulvat at Northwestern University in Evanston (USA) have now developed a new technique that forces conducting polymers into an ordered structure.
Various attempts to bring order to conducting polymers are currently being followed. Our previous press release (Nr. 06/2003) covered a solid state reaction in which a conducting polythiophene can be obtained -- with retention of shape - simply by heating the crystalline starting material. Stupp and Hulvat have also concentrated their research on polythiophenes, currently the most industrially important class of conducting polymers. However, they went about it in a completely different fashion; they had the polymerization reaction take place in the presence of a liquid crystal as a "template".
Liquid crystals are fluid phases in which the individual particles are spatially arranged as in a crystal, which means they are structured. The American researchers chose a liquid crystalline gel consisting of tiny, mutually parallel, hydrophobic (water repellent) cylindrical units, which are floating in a hydrophilic (water liking) environment. The building blocks for the polymer are dissolved in a thin layer of this gel. Because the building blocks are hydrophobic, they stay exclusively within the hydrophobic cylinders. The polymerization of the building blocks is then initiated with the help of an electric current. This doesn't change their distribution within the "template"; removal of the gel leaves behind a thin polythiophene film that mirrors both the texture and the optical properties of the liquid crystal. Stupp says: " Our very simple new method could help in the production of conducting plastics with improved electronic properties."