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>_<i>EM</i> 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>₂ 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., TiO₂ 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 TiO₂ 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 TiO₂ 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>_w = 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