Vapor-phase polymerization
The EDT monomer (Baytron M) and Fe(III) tosylate (40% solution in butanol,
Baytron C) were received from Bayer AG. p-Toluenesulfonic acid (PTSa) and
pyridine were obtained from Aldrich. All chemicals were used as received. PET foil
with a thickness of 125 mm was used as the substrate for the vapor-phase
polymerization of EDT. The PET was cleaned twice in ethanol before use.
Vapour-phase polymerization was carried out in a simple single-chamber set-up as
shown in Fig. 1. The chamber was flushed with 50 ml/min nitrogen during
polymerization, and a heater provides the possibility to raise the temperature of
the monomer reservoir to 50 1 C in order to speed up the process. The samples to be
covered with PEDOT are initially coated with the oxidant ferric tosylate. Ferric
tosylate in a high concentration (75% vol) in butanol has an adequate viscosity for
screen printing. Pyridine was added as basic inhibitor as described earlier [16] and
5% (vol) glycerin was added to control the speed of evaporation after the screen
printing. After drying at 80 1 C in air for 1 min, the samples were transferred to the
polymerization chamber. The vapour-phase polymerization continues for 45 min,
and thereafter the samples were heated to 50 1 C on a hot plate for 30 min and washed
twice in ethanol for 10 min.
The polymer coatings on the substrates were characterized by UV-vis spectro-
scopy (Shimadzu UV1700). The conductivity of the samples was measured using a
four-point probe from Jandel Engineering Ltd. connected to a Keithly 2400 source
meter. The probe was equipped with four spring-loaded tungsten carbide needles