T. Jana et Ak. Nandi, Sulfonic acid doped thermoreversible polyaniline gels. 2. Influence of sulfonic acid content on morphological, thermodynamical, and conductivity properties, LANGMUIR, 17(19), 2001, pp. 5768-5774
Thermoreversible gelation behavior of polyaniline (PANI) in the presence of
varying concentrations of sulfonic acids are studied. Four different sulfo
nic acids are used, e.g., dinonylnaphthalene sulfonic acid (DNNSA), dinonyl
naphthalene disulfonic acid (DNNDSA), (+/-)-camphor-10-sulfonic acid TSA),
and n-dodecyloxo sulfonic acid (DOSA). The composition range studied here i
s W-PANI = 0.05-0.80 (W-PANI is the weight fraction of PANI in the gel). It
has been found from the SEM study that for all the sulfonic acids in the c
omposition range W-PANI = 0.05-0.40, fibrillar network is present. The TEM
study also supports the above viewpoint. The thermodynamic study of the gel
s has been done by DSC-7, and for all the systems broad peaks consisting of
two fused gel melting/gel formation peaks are observed. After proper decon
volution of the two peaks the gel melting/gel formation temperatures are me
asured. When they are plotted with W-SO3H (weight fraction of sulfonic acid
), typical phase diagrams consisting of two almost parallel curves are foun
d. They are explained by considering the lamellar model where the bilayer a
nd monolayer portions of the surfactant form different crystalline domains.
The higher melting point curve is due to the former and the lower one is d
ue to the later in each phase diagram. The lowering of gel melting/gel form
ation points with increase in PANI concentration of each curve has been att
ributed to the dilution effect of PANI in the gel. The corresponding enthal
py values (DeltaH also show similar decrease with increasing PANI concentra
tion and are explained also from the dilution effect of PANI. The conductan
ce of these gels varies with weight fraction of PANI (Wp-ANI), showing a ma
ximum, and it has been explained by considering that conductivity in the ge
l is due to both intrachain and interchain contributions. Attempt is made t
o discuss the above results by using a molecular model of the PANI-DOSA sys
tem with the help of MMX program.