Polyaniline-silica colloidal nanocomposites.
The work presented in this thesis provides a new route to a colloidal form of polyaniline,
which uses colloidal silica as a dispersant. We obtained stable colloidal dispersions of
polyaniline-silica composite particles with a 'raspberry' morphology. Compressed pellets
of these particles exhibit solid-state conductivities of 1O-!_10-2 S crrr l, which is
approximately 1-2 orders of magnitude lower than that of polyaniline bulk powder. This
novel colloidal form of polyaniline has significantly improved processability compared to
conventionally synthesised polyaniline.
The synthesis and chemical characterisations are presented for various polyaniline-silica
colloidal nanocomposites. The quantity of polyaniline incorporated into the
nanocomposite particles can be controlled by varying the diameter of the silica
dispersant, approximately 20% and 60 % polyaniline content being obtained using 120
nm and 10 nm diameter silica respectively. The average particle size ranges of
nanocomposites was found to be 150 to 700 nm and 330 to 560 nm, as determined by
transmission electron microscopy (TEM) and disc centrifuge photosedimentometry
(DCP) respectively. The nanomorphology and surface composition of the polyanilinesilica
particles were determined by small angle X-ray scattering (SAXS) and X-ray
photoelectron spectroscopy (XPS) respectively. The average inter-particle separation
distance of the silica particles within the polyaniline-silica raspberries was determined by
SAXS to be 4 nm, a dimension equivalent to molecular polyaniline. The XPS data
suggests that the surface of the particles is silica rich, this is consistant with their long
term colloidal stability in 1.2 mole dm-3 HCl.
The kinetics of polymerisation was studied using 1H NMR spectroscopy to monitor the
disappearance of aniline monomer. Polymerisation rates during the synthesis of
polyaniline-silica nanocomposites were appreciably faster than the corresponding
precipitation polymerisations carried out in the absence of silica dispersants, due
primarily to an increase in the second auto-catalytic step of the reaction. Rate constants
were determined for both these types of synthesis; the values obtained for the
precipitation polymerisations were in reasonably good agreement with literature values.