Chemistry Reference
In-Depth Information
Several reports describe the mechanism of polymerisations using cerium
compounds in combination with alcohols
77,78
,diols
79,80
and polyols
81
. Only in
a limited number of kinetic studies was the concentration of cerium ions
measured during the polymerisation reaction. Mohanty
et al.
80
,Rout
et al.
81
,
Jayakrishnan
et al.
65
and Gupta and Behani
.
67
followed the reduction of
Ce(IV) ions titrimetrically.
To our present knowledge, there has been no detailed report so far study-
ing the initiation step of the synthesis of PEO block co-polymers continu-
ously. Here, a new method is presented that allows the determination
on-line of the consumption of Ce(IV) ions in the reaction mixture by means
of chronoamperometry and a flow injection analysis system using textile
electrodes with a gold surface.
12.4.2 Modification of textile fibres to obtain
gold-coated fibres
Common textile fibres, such as nylon, polyester and polyaramide fibres, can
be modified with a metallic layer in order to provide the modified fibre with
electroconductive properties. In the literature
82-85
,a respectable number of
papers were found to modify such fibres with polypyrrol, starting from the
adsorption of pyrrol, followed by the oxidative induced polymerisation of
pyrrol to polypyrrol. This initiation was obtained with FeCl
3
. In the work
described here, a polyaramide woven structure was modified. The adsorp-
tion step was accelerated by using ultrasound to promote the impregnation
of pyrrol into the woven structure of the polyaramide fibres. Polypyrrol
forms a suitable substrate for further deposition of a metallic layer. Simi-
larly with chemical copper deposition
82-85
, gold was deposited on the
polypyrrol substrate. This gold-modified structure was finally used as an
electrode.
These electrodes were positioned in electrochemical cells as described in
Chapter 9, with the difference that the modified gold electrode was posi-
tioned at one side of the tube (working electrode), a platinum net at the
other side (counter electrode) and a reference electrode in the middle of
the tube. The solution was pumped through this cell in order to obtain a
steady-state current signal (time-independent signal).
12.4.3 Electrochemical behaviour of Ce(IV) at the gold-
coated textile structure
The electrochemical behaviour of Ce(IV) at a gold-coated textile structure
was investigated by cyclic voltammetry in a 1.0 mol l
-1
H
2
SO
4
solution (Fig.
12.13). The potential is swept in positive direction from an initial potential
of -0.2 V vs. Ag|AgCl to a vertex potential of 1.7 V vs. Ag|AgCl and in the
