No abstract

Polyaniline can be inserted in V2O5·nH2O xerogel by in situ oxidative polymerization/intercalation of aniline or anilinium in air. The reaction is facile and topotactic, forming polyaniline as the emeraldine salt. The interlayer separation (5.6 Å) is consistent with a monolayer of polymer chains in the V2O5 framework. Evidence is presented that oxygen acts as an electron acceptor both during the in situ reaction and long after intercalation is complete. The crucial role of oxygen in this reaction is probed and discussed. In an alternative route, anilinium is first intercalated and then, in a second step, is oxidatively polymerized in the xerogel upon exposure of the intercalate sample to air. Upon standing in air (aging), two processes occur independently in these materials:  (a) the partial reoxidation of the reduced V2O5 framework and (b) further oxidative coupling of anilinium and aniline oligomers inside the V2O5 layers, leading to longer chain molecules. These observations are supported by several physicochemical data. The magnetic moment of (PANI) x V2O5·nH2O decreases gradually upon exposure to air, but it does not change when the sample is stored in vacuum. Gel permeation chromatography (GPC) analysis results show that the molecular weight of polyaniline extracted from aged (PANI) x V2O5·nH2O is larger than that extracted from the fresh samples. The thermal stability of polyaniline extracted from aged (PANI) x V2O5·nH2O is better than that extracted from fresh samples. All (PANI) x V2O5·nH2O samples are paramagnetic with a Curie−Weiss and a temperature-independent van Vleck contribution. Variable-temperature 2H-wide-line NMR of (PANI) x V2O5·nH2O shows that the polymer chains are sterically confined with respect to phenyl ring rotation. The room-temperature conductivity of the freshly prepared (PANI) x V2O5·nH2O samples is in the range 10-4−10-1 S/cm depending on the degree of polymerization inside the layers, but the conductivity of aged samples is always greater. Room temperature thermoelectric power is negative and varies (−30 to 200 μV/K) depending on the polymer content and the degree of polymerization.

No abstract

The intercalation of poly(ethylene oxide) (PEO) in layered V 2 O 5 xerogel and the structural and physicochemical characterization of the products is reported. The synthesis of PEO/ V 2 O 5 nanocomposites is achieved by simply mixing aqueous solutions of PEO with aqueous V 2 O 5 gels followed by slow water evaporation. Several different phases of PEO/V 2 O 5 composites can be obtained by varying the component ratios. The interlayer distance of (PEO) x V 2 O 5 ‚nH 2 O varies from 13.2 Å, at x ) 0.5, to 16.8 Å at x ) 1.0, to 17.6 Å at 1 < x < 3, and to 18.3 Å at x g 3. One-dimensional electron density calculations based on X-ray diffraction data (perpendicular to layers) show that the composites contain a monolayer of PEO molecules when x < 1 and a bilayer when x g 1. The data suggest that the PEO chains are arranged side-by-side in a fully extended conformation between the layers forming corrugated mono-or bilayers. The (PEO) x V 2 O 5 ‚nH 2 O intercalation compounds are water swellable and light-sensitive. UV irradiation causes dramatic changes in the electronic structure of V 2 O 5 and results in enhanced electrical conductivity and decreased solubility. The conductivity of the irradiated products decreases as the PEO content increases. The optical absorption spectra, electrical conductivity, thermoelectric power, magnetic susceptibility, and electron paramagnetic resonance spectra of the irradiated products are self-consistent and suggest an increased V 4+ concentration in the layers and n-type charge transport. Lithium ion redox intercalation was performed on the PEO/V 2 O 5 composites by reaction with LiI. Variable-temperature 7 Li solid-state NMR studies of the Li/PEO/V 2 O 5 materials are reported.

No abstract

No abstract

No abstract

Protonated emeraldine [poly(aniline)] has been encapsulated in Moo3 by first inserting aniline into its lattice followed by successful polymerization with (NH4)2S208; the new material is characterized by X-ray diffraction, IR spectroscopy, scanning electron microscopy and charge transport measurements.