We present the first theoretical calculations of the electronic structure of long (200 rings) linear chains of polyaniline, ranging in composition from leucoemeraldine to emeraldine, allowing for compositional disorder in that the sequence of quinoid-benzenoid groups is random. We show that random protonation of the disordered polymers may induce p-type conductivity: This process pulls the Fermi energy down into the valence band, past localized band tails, to extended states. The effect is only seen if disorder is taken into account. PACS numbers: 72.15.Nj, 71.20.HkThe interest in polyanilines stems from the fact that a dramatic increase in conductivity 1 ' 2 (up to 10 Scm -1 ) can be gained by acidic treatment (decreasing of the pH of the medium) or by electrochemical oxidation, or both. 3 The name polyaniline encompasses a family of compounds where nitrogen atoms connect six-membered carbon rings of benzenoid or quinoid character. The relative proportion of these groups may range from the totally reduced variety leucoemeraldine [ Fig. 1(a)] where only benzenoid structures exist, through emeraldine [Fig.

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The evolution in the static longitudinal polarizability and second hyperpolarizability of the C 4 H 2 through C 54 H 2 oligomers of polyyne is studied at the Hartree-Fock level of theory. We find that the calculated values are highly sensitive to the adopted geometry. Using improved geometries, new extrapolation procedures and careful finite field determinations we extend earlier work by others so as to provide reliable estimates for the above properties in the infinite polymer limit.

We describe the in situ preparation of a multipurpose hierarchical polyaniline-polystyrene (PANI-PS) composite based in the chemical polymerization of PANI on nonwoven (NW) electrospun PS mats. We performed a detailed study of the properties of these materials to select the best strategies to incorporate PANI chains into pristine NW PS mats without compromising the original porosity and mechanical flexibility of the matrices. The resulting composites presented nanostructured PANI chains highly dispersed in the interior of the NW PS mat and showed good electrical properties and surface-wetting characteristics that could be easily controlled. In particular, we show that these NW PANI-PS mats exhibit interesting properties in their interaction with heavy metal ions. For instance, their high adsorption capacities toward dispersed Hg(II), Cd(II), Pb(II), Cr(VI), and Cu(II) ions make them promising materials for water remediation, by providing a simple manner of collecting and removing these metals from aqueous systems. In fact, the NW electrospun mats here presented do not suffer from the usual limitations found in materials commonly employed as adsorbents, such as a tendency to agglomerate or accumulate in the environment because of difficulties of properly recovering them after use. To better understand the nature of each pairwise metal-PANI interaction, we performed a thorough investigation of the optical and electrical changes induced by the metal adsorption in the NW PANI-PS mats. As a consequence of their interaction with the metal ions, the visual aspect of the mats change, a fact more evident in the case of Cr(VI) removal, when the matrices vary their color from green to purple. These changes are related to the variation of the oxidation state of the PANI chains: as the ion metals are progressively adsorbed into the mat, they promote the conversion in varying degrees of the PANI chains from salt emeraldine to the pernigraniline form, and the mats become more resistive. We implemented an electrical impedance investigation of the charge transport characteristics of NW PANI-PS mat, and the results indicate that they are sensitive to the type of metal ion adsorbed and that the amount of ions adsorbed in each case is mostly related to the standard electrode potential of the metal considered.

Flexible batteries and supercapacitors (SCs) are expected to play a crucial role in energy storage and management in portable electronic devices. In addition, use of materials based on renewable resources would allow for more affordable and sustainable gadgets. In this context, eggshell membranes (ESMs) represent a promising functional platform for production of high-performance electronic components. In this work, we use ESMs for preparing flexible SCs through the incorporation of carbon nanotubes and subsequent in situ polymerization of polypyrrole, producing a highly conductive nanostructure characterized by a porous surface that exhibits both faradic and nonfaradic mechanisms for charge storage. We have found that by controlling the conducting polymer/carbon derivative relative concentration, one can maximize the corresponding capacitance to attain values up to the order 564.5 mF/cm 2 (areal capacitance), 24.8 F/cm 3 (volumetric capacitance), and 357.9 F/g (gravimetric capacitance). These bioinspired flexible devices exhibit a capacitance retention of 60% after 4000 cycles of charge/discharge and present negligible aging even after 500 bending repetitions (at a density of current 5 mA/cm 2 ). The successful use of ESM-based electrodes in association with carbon derivatives/conducting polymers confirm that the exploit of biological materials offers a promising perspective for the development of new ecofriendly electronic devices.

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We use a perturbative density matrix treatment to investigate the behavior ofthe first and second static hyperpolarizabilities oflinear conjugated chains CNHN + 2 described by a Pariser-Parr-Pople Hamiltonian. We examine the evolution of the hyperpolarizabilities with increasing chain lengths, and the effect of different conformations (such as those corresponding to soliton and polaron defects) and of different charge states on the polarizabili.ty r~p~nse of the chains. It is s.hown that charged soliton chains have large first hyperpolanzabllttles /3, and that the behaVIOr of the different components of the second hyperpolarizability tensor riiii is highly dependent on the geometry and charge of the conjugated chain. In all cases, the contribution of the longitudinal component is shown to dominate the orientationally averaged hyperpolarizability of the chains.