S. Sakkopoulos et al., CONDUCTIVITY DEGRADATION DUE TO THERMAL AGING IN CONDUCTING POLYANILINE AND POLYPYRROLE, Synthetic metals, 92(1), 1998, pp. 63-67
The decrease of the electrical conductivity of polyaniline and polypyr
role due to thermal aging is reported. The d.c. conductivity is measur
ed in the temperature range 300-80 K for aging times from 0 to 11 h at
120 degrees C in room atmosphere. The conductivity of polyaniline dec
reases with aging time according to the law sigma = sigma(o)exp[-(t/ta
u)(1/2)]. Polypyrrole diverges either from the above or sigma(o)-sigma
alpha t(1/2). Moreover, polyaniline follows sigma = sigma(o)exp[-(T-o
/T)(1/2)] law with T-o increasing with aging time. This can be explain
ed by a conduction mechanism consisting of electron tunnelling between
conducting grains embedded into an insulating matrix. Polypyrrole fol
lows a sigma = sigma(o)exp[-T-1/(T + T-o)] law until about 5 h of agin
g time. For longer heating its behaviour diverges from the predictions
of known models of conduction in polymers. The above can be attribute
d to differences of the aging process in the two compounds. In polyani
line, aging is accompanied simply by a decrease of the grain size, the
separation of which increases from 27 to 54 Angstrom after 10 h of he
ating at 120 degrees C. In polypyrrole, for short aging times, the gra
in size remains constant, their separation being about 60 Angstrom. Lo
nger aging leads to a thermally activated conductivity whose mechanism
is obscure. (C) 1998 Elsevier Science S.A.