A suitable model for emeraldine salt

Effect of face-to-face and side-to-side interchain interactions on the electron transport in emeraldine salt polyaniline

Polyaniline (PANI) is a conductive polymer that has been studied intensively due to its high conductivity, ease of synthesis, fascinating doping mechanism, and a broad spectrum of applications. Polyaniline doped HCl was synthesized by a common direct-oxidation method of aniline using ammonium persulfate as the oxidant in HCl solution at various temperatures. This study focused on conductivity alteration of PANI-ES (emeraldine salt) due to the interchain interaction observed at different reaction temperatures from room temperature down to -15 °C. The molecular structure of PANI-ES was determined by FTIR and Raman spectroscopy. At low reaction temperature, the electronic transport properties improve significantly as reflected by its conductivity. X-ray diffraction (XRD) analysis shows that the value d_{(110)} and β play an important role in electron transport through face-to-face and side-to-side interactions, respectively. Scanning electron microscopy (SEM) analysis shows that the morphology of the synthesized PANI-ES consists of granules that are interconnected by nanofibers. Here, the correlation between electronic transport properties, structure, and morphology induced by reaction temperature was analyzed and discussed in detail. Moreover, PANI ES synthesized at 0 °C was applied as an electrocatalytic active layer in the DSSC's counter-electrode with a promising result.

First-principles study of the effect of functional groups on polyaniline backbone

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.

Nano approach investigation of the conduction mechanism in polyaniline nanofibers

A nanotechnological approach is applied to measurements of the electric field dependence of resistance under a high electric field while in low voltage. With this technique, the conduction mechanism on a mesoscopic scale is explored in a single, nonagglomerated nanofiber. Polyaniline nanofibers are prepared by vigorous mixing of aniline and oxidation agent ammonium persulfate in acid solution. They exhibit a uniform nanoscale morphology rather than agglomeration as that produced via conventional chemical oxidation. The as-synthesized polyaniline nanofibers are doped (dedoped) with a HCl acid (NH(3) base), and their temperature behaviors of resistances follow an exponential function with an exponent of T(-1/2). To measure the conduction mechanism in a single nanofiber, the dielectrophoresis technique is implemented to position nanofibers on top of two electrodes with a nanogap of 100-600 nm, patterned by electron-beam lithography. After the devices are irradiated by electron beam to reduce contact resistances, their temperature behaviors and electric field dependences are unveiled. The experimental results agree well with the theoretical model of charging energy limited tunneling. Other theoretical models such as Efros-Shklovskii and Mott's one-dimensional hopping conduction are excluded after comparisons and arguments. Through fitting, the size of the conductive grain, separation distance between two grains, and charging energy per grain in a single polyaniline nanofiber are estimated to be about 4.9 nm, 2.8 nm, and 78 meV, respectively. The nanotechnological approach, where the nanogap and the dielectrophoresis technique are used for single nanofiber device fabrication, is applied for determination of mesoscopic charge transport in a polyaniline conducting polymer.