Polyaniline as a Precursor of Multi-Layer Graphene: Microscopic and Microspectroscopic Study.

Aluminosilicate-based nanocomposites containing multi-layer graphene were prepared from polyaniline/montmorillonite intercalate in two different forms: tablets and thin layers. Starting materials, polyaniline/montmorillonite powder and polyaniline/montmorillonite layers deposited on quartz glass, were prepared by in situ polymerization of aniline in presence of montmorillonite particles. Powder was compacted into tablets using pressure 400 MPa. Samples were calcined at 1300 °C in argon atmosphere and multi-layer graphene was formed from polyaniline in both cases as confirmed by Raman microspectroscopy. Changes in morphology and surface conductivity of uncalcined and calcined samples were observed using atomic force microscopy and conductive atomic force microscopy. Also the differences between surface and internal volume of tablets were studied. Conductive atomic force microscopy revealed that the most conductive areas can be found solely on the edges of aluminosilicate particles formed from montmorillonite during calcination process. Detailed observation of multi-layer graphene in these areas was performed using transmission electron microscopy.

Stevensite-Rich Moroccan Clay Intercalated by Polypyrrole: Towards the Enhancement of Electrical Conductivity.

Regularly arranged chains strongly affect the electrical conductivity of conductive polymers (e.g., polypyrrole). One of the easiest ways to achieve this arrangement is the insertion of the polymer into the interlayer space of solid inorganic layered matrix, i.e., the intercalation process. Among various kinds of layered materials, the clay minerals, especially the smectite group, deserves particular attention. Negative charge of smectite layers helps the intercalation process resulting in higher conductivity of the polymer in clay/polymer intercalates. Characterization of stevensite-rich Moroccan clay and intercalation of electrically conductive polypyrrole into stevensite-rich Moroccan clay in order to obtain material with higher conductivity in comparison with pure polypyrrole were two main purposes of this work. Two forms of stevensite/polypyrrole nanocomposites were studied: powder and pressed tablets. X-ray fluorescence spectroscopy, X-ray diffraction analysis, atomic force microscopy, thermogravimetry, infrared spectroscopy, Raman microspectroscopy, and scanning electron microscopy in conjunction with energy dispersive X-ray spectroscopy were used to study the composition and structure of the nanocomposites. Measurement of electrical conductivity of polypyrrole in stevensite/polypyrrole nanocomposites revealed enhanced conductivity for all samples and also anisotropy in the conductivity of the samples pressed in the tablets.

Surface and interlayer structure of vermiculite intercalated with methyl viologen.

Molecular modeling using empirical force field revealed the differences between the surface and interlayer arrangement of the dye guest molecules in vermiculite intercalated with the divalent methyl viologen cation (MV(2+)). Conformation and anchoring of MV(2+) cations on the silicate layer in the interlayer space of vermiculite host structure is different from that on the crystal surface. A preferential position has been found for the anchoring of guests on the silicate layer. Anyway the arrangement of guests in the interlayer space as well as on the crystal surface exhibits a high degree of disorder due to a certain flexibility in guest molecules arrangement and first of all due to the presence of water molecules in the interlayer space. The presence of water disturbs not only the regularity in guest positions and orientations but also in conformation of guest molecules in the interlayer space of the host structure.

Fluorescence and structure of methyl red-clay nanocomposites.

Two types of clay minerals-montmorillonite and vermiculite have been chosen as a host matrix for the intercalation of methyl red (MR) in order to investigate a possible fluorescence tuning via dye-clay interactions. The effect of silicate layer charge on the structure and fluorescence of dye-clay intercalated hybrid nanostructures was investigated using combination of molecular modeling with experiment. Structure of both intercalates MR-vermiculite (MR-VER) and MR-montmorillonite (MR-MMT) exhibits high degree of structural disorder resulting in broaden emission band. The fluorescence wavelength range of MR intercalated in clays is shifted to lower wavelengths compared with the pristine MR polycrystalline sample (800 nm). Results showed the strong dependence of fluorescence band maximum on the silicate layer charge, lambda(max) = 565 nm for MR-MMT, 645 nm for MR-VER and 800 nm for the methyl red fine crystalline powder, whereas the structural disorder in the arrangement of dye molecules affects the emission band broadening.