4 research outputs found
Effect of Multiwalled Carbon Nanotubes on the Kinetics of the Aniline Polymerization: The Semi-Quantitative OCP Approach
We
demonstrate applicability of the open-circuit potential (OCP) method
for kinetic analysis of the oxidative chemical polymerization of aniline
both in clear solution and in dispersions of multiwalled carbon nanotubes
(MWCNT). The characteristic points and the shape of the OCP profile
are used to estimate the kinetic parameters of the main stages of
the known two-step polymerization mechanism of aniline. We have found
that the reciprocal values of the duration of the main polymerization
stages namely the induction period, pernigraniline (PN) accumulation
and reduction of PN with residual aniline are the linear functions
of the weight fraction of MWCNT. To compare the kinetic data of the
proposed OCP and known approaches the last two stages have been considered
as a single heterogeneous stage of emeraldine (EM) formation. The <i>k</i><sub><i>EM</i></sub> rate constant calculated
by the OCP profiles for this EM stage in the solution and dispersion
media is in a very good agreement with the known <i>k</i><sub>2</sub> values
Influence of Dispersed Nanoparticles on the Kinetics of Formation and Molecular Mass of Polyaniline
Using a combination of the open circuit
potential and pH profiles
of aniline (An) polymerization and their mathematical treatment, we
develop a new convenient semiquantitative approach to determine the
influence of the dispersed nanoparticles (e.g., TiO<sub>2</sub> nanoparticles)
on the kinetic features of this process and molecular mass of the
formed polyaniline (PANI). It is revealed
that the reciprocal values of the polymerization stages, namely, the
duration of the induction period, of homogeneous and heterogeneous
pernigraniline (PN) accumulation, and of PN reduction with An, are
linear functions of the weight fraction of the nanoparticles. We found
that when nanoparticles are added the weight-averaged molecular weight
of PANI initially increases from 56 000 to 79 000 and
the polydispersity index drops from 3.9 to 1.7. However, at high TiO<sub>2</sub> concentrations, the former dramatically decreases, whereas
the latter increases. We use the relative proton concentration as
a function of time and the different extents of acceleration of the
consecutive stages of An polymerization to explain the changes in
the molecular weight distribution of PANI with different contents
of TiO<sub>2</sub> nanoparticles in the polymerization medium
Deep Impact of the Template on Molecular Weight, Structure, and Oxidation State of the Formed Polyaniline
In
this work we find that polyaniline (PANI), synthesized by aniline
chemical polymerization at a surface of template polycarbonate (PC)
particles, is significantly different in molecular weight, structural
order, oxidation state, and conductivity from a neat PANI. Molecular
weight of the PANI phase in the composite (<i>M</i><sub>w</sub> = 158 000) is 1.6 times higher than that of the neat
PANI synthesized in the absence of the template particles. Moreover,
XRD analysis shows that crystallinity of the PANI phase in the composite
is three times higher than that of the neat PANI. Raman spectroscopy
indicates that the oxidation level of PANI in the PC/PANI composite
is lower than that of the neat PANI. These noticeable changes of the
PANI phase properties suggest specific interactions of reagents in
the polymerization medium and formed PANI with the template phase
as well as an orientation effect of the latter surface. FTIR spectroscopy
reveals that hydrogen bonding in the neat doped PANI is weaker than
one between −NH– of PANI and CO of PC at their
interface. The discovered differences are supported by the fact that
conductivity of the PANI phase in the composite is more than three
times higher than that of the neat PANI
Evolution and Interdependence of Structure and Properties of Nanocomposites of Multiwall Carbon Nanotubes with Polyaniline
Structure–property
relationships of nanocomposites of multiwall
carbon nanotubes (MWCNTs) and polyaniline (PANI) doped with dodecylbenzenesulfonic
acid (DBSA) are studied and discussed in terms of contribution of
the PANI phase properties. Two phases of PANI-DBSA with different
properties, such as a shell-wrapping carbon nanotube and separate
neat PANI-DBSA domains, are revealed for the first time in the nanocomposites
with a high or medium PANI-DBSA content. In the nanocomposites with
lower PANI-DBSA contents (<40 wt %), only a core–shell morphology
with ∼3 nm or lower thickness PANI shell on the nanotubes is
observed. Under this condition, the degree of crystallinity of the
PANI-DBSA shell increases almost 2-fold, and thermal stability of
the nanocomposite grows sharply. As compared with the neat PANI-DBSA,
this special PANI shell phase has more perfect molecular structure
and is characterized by a reduced amount of DBSA. It is found that
the latter is caused by a competition between the processes of doping
of the formed PANI in the shell by the protonic acid and p-doping
caused by the MWCNT surface. The nanocomposites demonstrate ppm/ppb
range sensitivity to ammonia/methylamine gases with response times,
which inversely depend on the PANI-DBSA contents and thickness of
the shell