Abstract
We present a first-principles density functional theory study focused on how the chemical and electronic properties of polyaniline are adjusted by introducing suitable substituents on a polymer backbone. Analyses of the obtained energy barriers, reaction energies and minimum energy paths indicate that the chemical reactivity of the polyaniline derivatives is significantly enhanced by protonic acid doping of the substituted materials. Further study of the density of states at the Fermi level, band gap, HOMO and LUMO shows that both the unprotonated and protonated states of these polyanilines are altered to different degrees depending on the functional group. We also note that changes in both the chemical and electronic properties are very sensitive to the polarity and size of the functional group. It is worth noting that these changes do not substantially alter the inherent chemical and electronic properties of polyaniline. Our results demonstrate that introducing different functional groups on a polymer backbone is an effective approach to obtain tailored conductive polymers with desirable properties while retaining their intrinsic properties, such as conductivity.
Highlights
We present a first-principles density functional theory study focused on how the chemical and electronic properties of polyaniline are adjusted by introducing suitable substituents on a polymer backbone
We demonstrated that the introduction of –OH and –SO3Na groups at the phenyl rings leads to a remarkable improvement in the chemical reactivity for the protonation of polyaniline by equilibration with H2CO3
We observed that the hybridization between the functional group and the phenyl ring induces an impurity state near the Fermi level and band gap changes in the carbonate salts of polyanilines
Summary
A half-oxidized polymer[1], emeraldine base of polyaniline (EB-PANI), was used as the parent polyaniline. The finite molecular models for these polyanilines in their unprotonated and H2CO3-protonated states are schematically represented, respectively. The periodic molecular models for polyanilines in unprotonated and H2CO3-protonated states are depicted, respectively. The calculations of the density of states at the Fermi level N(E) and the band gap Eg were performed using the DMol[3] package and DFT-D based on GGA-PBE. To consider the temperature effect on the electronic properties as addressed in our previous study[11,22], the initial optimization of the periodic molecular model by DMol[3] was followed by running a canonical ensemble-molecular dynamics (NVT-MD) for 50 ps (time step = 0 .001 ps) at room temperature (298 K) using the Forcite[23] package of Materials Studio, and the commercial force field “COMPASS II” was used to evaluate the atomic forces. The summation methods “atom-based” with a cutoff value of 12.5 Å and “Ewald” were employed for the non-bonded van der Waals (vdW) and electrostatic (or Coulomb) interactions, respectively
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