Oxidation of anilinium ions intercalated in montmorillonite clay by electrochemical route

Resonance Raman, FTIR, X-ray diffraction, UV-vis-NIR, electron paramagnetic resonance, X-ray absorption at Si K-edge and electron microscopy were employed for characterizing the products formed through electrochemical oxidation of intercalated anilinium ions inside the cationic montmorillonite (MMT) clay. The layer silicate structure was not affected by the anilinium oxidation between the layers. The intercalated products present only an electronic absorption band at 400 nm, very low conductivity (ca. 10(-7) S cm(-1)) and their Raman spectrum displays bands, with high relative intensities, assigned to the benzidine dication, indicating that this product was formed in high amount. Nevertheless, bands that can be correlated to phenazine-like segments and 1,4-phenylenediamine repeat units (PANI like segments) are also observed. The very low EPR signal indicates that diamagnetic species are predominant. All results are compared to those obtained by anilinium-MMT chemically oxidized by persulfate and the differences are pointed out. (C) 2008 Elsevier B.V. All rights reserved.

Bacterial cellulose-laponite clay nanocomposites

A novel material comprised of bacterial cellulose (BC) and Laponite clay with different inorganic organic ratios (m/m) was prepared by the contact of never-dried membranes of BC with a previous dispersion of clay particles in water. Field emission scanning electron microscopy (FE-SEM) data of composite materials revealed an effective adhesion of clay over the surface of BC membrane; inorganic particles also penetrate into the polymer bulk, with a significant change of the surface topography even at 5% of clay loading. As a consequence, the mechanical properties are deeply affected by the presence of clay, increasing the values of the Young modulus and the tensile strength. However the maximum strain is decreased when the clay content is increased in the composite in comparison to pristine BC. The main weight loss step of the composites is shifted towards higher temperatures compared to BC, indicating that the clay particles slightly protect the polymer from thermal and oxidative decomposition. (C) 2010 Elsevier Ltd. All rights reserved.

Nuclear Magnetic Resonance Study of Hydrated Bentonite

Impedance spectroscopy and nuclear magnetic resonance (NMR) were used to investigate the mobility of water molecules located in the interlayer space of H(+) - exchanged bentonite clay. The conductivity obtained by ac measurements was 1.25 x 10(-4) S/cm at 298 K. Proton ((1)H) lineshapes and spin-lattice relaxation times were measured as a function of temperature over the temperature range 130-320 K. The NMR experiments exhibit the qualitative features associated with the proton motion, namely the presence of a (1)H NMR line narrowing and a well-defined spin-lattice relaxation rate maximum. The temperature dependence of the proton spin-lattice relaxation rates was analyzed with the spectral density function appropriate for proton dynamics in a two-dimensional system. The self-diffusion coefficient estimated from our NMR data, D similar to 2 x 10(-7) cm(2)/s at 300 K, is consistent with those reported for exchanged montmorillonite clay hydrates studied by NMR and quasi-elastic neutron scattering (QNS).

Structure of polyaniline formed in different inorganic porous materials: A spectroscopic study

In this work, the electronic and structural characterization of polyaniline (PANI) formed in cavities of zeolites Y (ZY) and Mordenite (MOR) and montmorillonite (MMT) clay having Cu(II) as oxidant agent are presented. The formation of PANI and its structure is analyzed by Resonance Raman, UV-Vis-NIR, FT-IR and N K XANES techniques. In all cases the structure of PANT formed is different from the ""free"" polymer. The presence of azo bonds linked to phenazine-like rings are observed only for PANI-MMT composites, independent of the kind of oxidant agent employed in the synthesis. The presence of Cu(II) ions leads to the formation of Phenosafranine-like rings. The presence of these phenazine-like rings in the structure of confined PANT chains can also contribute to the enhancement of the thermal stability observed for all composites. (C) 2008 Elsevier Ltd. All rights reserved.

Spectroscopic investigation of conjugated polymers derived from nitroanilines

For the first time, the resonance Raman spectroscopy was used to characterize polymers derived from meta- and para-nitroanilines. In order to improve the polymer structure analysis, other techniques were also used such as FTIR, UV-vis, XRD, XPS, EPR and N K-XANES. The insertion of strong electron-withdrawing groups (NO2) in polyaniline (PANI)-like backbone causes drastic changes in the lower energy charge transfer states, related to the polymer effective conjugation length. The resonance Raman data show that the NO2 moiety has a minor contribution on the CT state in poly(meta-nitroaniline), PMN, while in the poly(para-nitroaniline), PPN, the quinoid structure induced by para-substitution increases the charge density of NO2 groups, causing a more localized chromophore. The characterization of the imine nitrogen and of the protonated segments was done by XPS, N K-XANES and EPR spectroscopies and the lower polymerization degree of PPN, in comparison to PMN, is confirmed by XRD and TG data. (C) 2007 Elsevier B.V. All rights reserved.

Spectroscopic characterization of the structural changes of polyaniline nanofibers after heating

The thermal behavior of PANI nanofibers doped with beta-naphthalenesulfonic acid (beta-NSA) was investigated and their morphological and structural changes after heating were monitored by SEM, XRD and Raman techniques, respectively. By using electron-scanning microscopy it is possible to verify that the nanofiber morphology is stable and no polymer degradation is observed in thermogravimetric (TG) data up to 200 degrees C. Nevertheless, the heating promotes the formation of cross-linking structures (phenazine and/or oxazine-like rings), that is clearly demonstrated by the presence of bands at ca. 578, 1398, and 1644 cm(-1) in resonance Raman spectra of heated PANI-NSA samples. The most important consequence of the formation of cross-linking structures in PANI-NSA samples is that these samples retain their nanofiber morphology upon HCl doping in contrast to PANI-NSA nanofibers without heating. (c) 2007 Elsevier Ltd. All rights reserved.

Synthesis and spectroscopic characterization of polymer and oligomers of ortho-phenylenediamine

Poly(ortho-phenylenediamine) and oligomers of ortho-phenylenediamine were chemically synthesized and characterized by UV-vis, (1)H and (13)C NMR, FTIR and resonance Raman spectroscopies. Polymerization of ortho-phenylenediamine in HCl medium with ammonium persulfate only leads the trimer compound, in disagreement with some previous reports. Nevertheless, in acetic acid medium it was possible to prepare a polymer constituted by ladder phenazinic segments with different protonation levels and quinonediimine rings (polyaniline-like). X-ray absorption at N K-edge (N K XANES), X-ray photoelectron (XPS) and Electron paramagnetic resonance (EPR) spectroscopies were used to determine the different kinds of nitrogen presents in this class of polymer. N K XANES spectrum of poly(ortho-phenylenediamine) shows the band of -N=nitrogen of non-protonated phenazinic rings at 398.2 eV. In addition, XPS and N K XANES data confirm the presence of different types of protonated nitrogens in the polymeric poly(ortho-phenylenediamine) chain and the EPR spectrum shows that the polymer has a very weak polaronic signal. (C) 2009 Elsevier Ltd. All rights reserved.

Structure of chemically prepared poly-(para-phenylenediamine) investigated by spectroscopic techniques

The structure of chemically prepared poly-p-phenylenediamine (PpPD) was investigated by Resonance Raman (RR), FTIR, UV-VIS-NIR, X-ray photoelectron (XPS), X-ray Absorption at Nitrogen K edge (N K XANES), and Electron paramagnetic Resonance (EPR) spectroscopies. XPS, EPR and N K XANES data reveal that polymeric structure is formed mainly by radical cations and dication nitrogens. It excludes the possibility that PpPD chains have azo or phenazinic nitrogens, as commonly is supposed in the literature. The RR spectrum of PpPD shows two characteristic bands at 1527 cm(-1) and 1590 cm(-1) that were assigned to nu C=N and nu C=C of dication units, respectively, similar to polyaniline in pernigraniline base form. The presence of radical cations was confirmed by Raman data owing to the presence of bands at 1325/1370 cm(-1), characteristic of nu C-N of polaronic segments. Thus, all results indicate that PpPD has a doped PANT-like structure, with semi-quinoid and quinoid rings, and has no phenazinic rings, as observed for poly-o-phenylenediamine. (C) 2009 Elsevier Ltd. All rights reserved.

The role of cross-linking structures to the formation of one-dimensional nano-organized polyaniline and their Raman fingerprint

In the present work. the resonance Raman. UV-vis-NIR and scanning electron microscopic (SEM) data of nanorods (about similar to 300 rim in diameter) and nanofibers (about similar to 93 nm in diameter) of PANI are presented and compared. The PANI samples were synthesized in aqueous media with dodecybenzenesulfonic acid (DBSA) and beta-naphtalenesulfonic acid (beta-NSA) as dopants, respectively. The presence of hands at 578, 1400 and 1632cm(-1) in the Raman spectra of PANI-NSA and PANI-DBSA shows that the formation of cross-linking structures is a general feature of the PANI chains prepared in micellar media. It is proposed that these structures are responsible for the one-dimensional PANI morphology formation. In addition, the Raman band at 609cm(-1) of PANI fibers is correlated with the extended PANI chain coil formation. (C) 2008 Elsevier B.V. All rights reserved.

High Solids Content, Soap-Free, Film-Forming Latexes Stabilized by Laponite Clay Platelets

High solids content film-forming poly[styrene-co-(n-butyl acrylate)] [poly(Sty-co-BuA)] latexes armored with Laponite clay platelets have been synthesized by soap-free emulsion copolymerization of styrene and n-butyl acrylate. The polymerizations were performed in batch in the presence of Laponite and a methyl ether acrylateterminated poly(ethylene glycol) macromonomer in order to promote polymer/clay association. The overall polymerization kinetics showed a pronounced effect of clay on nucleation and stabilization of the latex particles. Cryo-transmission electron microscopy observation confirmed the armored morphology and indicated that the majority of Laponite platelets were located at the particle surface. The resulting nanostructured films displayed enhanced mechanical properties.

Influence of Granulometry and Organic Treatment of a Brazilian Montmorillonite on the Properties of Poly(styrene-co-n-butyl acrylate)/Layered Silicate Nanocomposites Prepared by Miniemulsion Polymerization

The influence of granulometry and organic treatment of a Brazilian montmorillonite (MMT) clay on the synthesis and properties of poly(styrene-co-n-butyl acrylate)/layered silicate nanocomposites was studied. Hybrid latexes of poly(styrene-co-butyl acrylate)/MMT were synthesized via miniemulsion polymerization using either sodium or organically modified MMT. Five clay granulometries ranging from clay particles smaller than 75 mu m to colloidal size were selected. The size of the clay particles was evaluated by Specific surface area measurements (BET). Cetyl trimethyl ammonium chloride was used as an organic modifier to enhance the clay compatibility with the monomer phase before polymerization and to improve the clav distribution and dispersion within the polymeric matrix after polymerization. The sodium and organically modified natural clays as well as the composites were characterized by X-ray diffraction analysis. The latexes were characterized by dynamic light scattering. The mechanical, thermal, and rheological properties of the composites obtained were characterized by dynamical-mechanical analysis, thermogravimetry, and small amplitude oscillatory, shear tests, respectively. The results showed that smaller the size of the organically modified MMT, the higher the degree of exfoliation of nanoplatelets. Hybrid latexes in presence of Na-MMT resulted in materials with intercalated structures. (C) 2009 Wiley, Periodicals, Inc. J Appl Polym Sci 112: 1949-1958, 2009

Influence of the Type of Quaternary Ammonium Salt Used in the Organic Treatment of Montmorillonite on the Properties of Poly(Styrene-co-Butyl Acrylate)/Layered Silicate Nanocomposites Prepared by In Situ Miniemulsion Polymerization

Hybrid latices of poly(styrene-co-butyl acrylate) were synthesized via in situ miniemulsion polymerization in the presence of 3 and 6 wt % organically modified montmorillonite (OMMT). Three different ammonium salts: cetyl trimethyl ammonium chloride (CTAC), alkyl dimethyl benzyl ammonium chloride (Dodigen), and distearyl dimethyl ammonium chloride (Praepagen), were investigated as organic modifiers. Increased affinity for organic liquids was observed after organic modification of the MMT. Stable hybrid latices were obtained even though miniemulsion stability was disturbed to some extent by the presence of the OMMTs during the synthesis. Highly intercalated and exfoliated polymer-MMT nanocomposites films were produced with good MMT dispersion throughout the polymeric matrix. Materials containing MMT modified with the 16 carbons alkyl chain salt (CTAC) resulted in the largest increments of storage modulus, indicating that single chain quaternary salts provide higher increments on mechanical properties. Films presenting exfoliated structure resulted in the largest increments in the onset temperature of decomposition. For the range of OMMT loading studied, the nanocomposite structure influenced more significantly the thermal stability properties of the hybrid material than did the OMMT loading. The film containing 3 wt % MMT modified with the two 18 carbons alkyl chains salt (Praepagen) provided the highest increment of onset temperature of decomposition. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 3658-3669, 2011

Montmorillonite as a component of polysulfone nanocomposite membranes

Nanocomposite membranes containing polysulfone (PSI) and sodium montmorillonite from Wyoming (MMT) were prepared by a combination of solution dispersion and the immersion step of the wet-phase inversion method. The purpose was to study the MMT addition with contents of 0.5 and 3.0 mass% MMT in the preparation of nanocomposite membranes by means of morphology, thermal, mechanical and hydrophilic properties of nanocomposite membranes and to compare these properties to the pure PSf membrane ones. Small-angle X-ray diffraction patterns revealed the formation of intercalated clay mineral layers in the PSf matrix and TEM images also presented an exfoliated structure. A good dispersion of the clay mineral particles was detected by SEM images. Tensile tests showed that both elongation at break and tensile strength of the nanocomposites were improved in comparison to the pristine PSf. The thermal stability of the nanocomposite membranes, evaluated by onset and final temperatures of degradation, was also enhanced. The hydrophilicity of the nanocomposite membranes, determined by water contact angle measurements, was higher; therefore, the MMT addition was useful to produce more hydrophilic membranes. (C) 2009 Elsevier B.V. All rights reserved.

Polyethylene/(organo-montmorillonite) composites modified with ethylene/ methacrylic acid copolymer: Morphology and mechanical properties

Several composites based on high-density polyethylene (PE), organically modified montmorillonite (OMMT) and ethylene/methacrylic acid copolymer (EMAA) were prepared by melt compounding. Three Na(+)-montmorillonites (MMT) of different precedence were modified with hexadecyl trimethyl ammonium chloride in order to change their nature from hydrophilic to organophilic. The composites morphology was examined by XRD, SEM and TEM. Mechanical properties were evaluated under static conditions. A slight reinforcement was achieved only when OMMT was added to PE. When EMAA was added to the composites, it negatively interacted with OMMT, diminishing the interlayer distance of OMMT, changing the composite morphology, as if OMMT was not present in composites, and deteriorating their mechanical properties. (C) 2008 Elsevier Ltd. All rights reserved.

Photooxidative behavior of polystyrene-montmorillonite nanocomposites

The weathering behavior of polystyrene and polystyrene-montmorillonite composites containing 2.5, 5.0, and 7.5 wt% of montmorillonite (MMT) was investigated. Samples were exposed to UV radiation for periods of up to similar to 12 weeks and their molecular weight, chemical changes, and mechanical properties were monitored as a function of time. The addition of MMT was shown to improve the photostability of all composites investigated, probably because of a screen effect against UV radiation and barrier effect against diffusion of oxygen promoted by the silicate layers of MMT. Scanning electron microscopy of fracture surfaces of degraded samples showed that there is a degraded layer near the surface that provided a recovery of tensile strength of the samples.