Lenka Kulhánková

Fluorescence of reduced charge montmorillonite complexes with methylene blue: Experiments and molecular modeling

The intensity of fluorescence of montmorillonites fully saturated by methylene blue (MB) is very poor due to energy dissipation in MB aggregates. A series of reduced charge montmorillonites (RCM) were prepared from Na-homoionic SWy and Ca homoionic SAz with the aim to decrease the MB aggregation. Fine tuning MB adsorption degree by charge reduction and MB concentration enabled controlled production of different dye species from aggregates via dimers to monomers. It was shown that the intensity of the fluorescence of low-loaded MB-RCM complexes is enhanced by several orders of magnitude with respect to dye-saturated original montmorillonites. XRD analyses, molecular modeling, and diffuse reflectance spectroscopy revealed that low MB-loaded RCMs are very probably adsorbed mainly on the external montmorillonite surface as isolated dye molecules. Such a state cannot be achieved in the solid state without very careful tailoring of the host-guest interaction.

Breakup of Bubbles Rising in Liquids of Low and Moderate Viscosity

ABSTRACT The breakup rate of bubbles was studied by observing them rising in water and in glycerol solutions with μ = 1–32 mPas. A levitating technique was applied with bubbles seized in the downstream liquid flow of a diverging channel. Bubbles with volumes V B = 0.2–0.8 cm3 are generally spheroid but their shape pulsates. As they wobble they have a tendency to split. The exponential decay of the number of unbroken bubbles was found, which has been characterized quantitatively by a half-life, t 1/2. The rate of breakup increased significantly with the original size of the bubble. By regression of experimental data, the proportionality t 1/2 ∼ V B −4 has been determined. There is a significant effect of surface tension, while the effect of viscosity on the process appeared to be negligible in the bubble Reynolds number range of 60–3000 that was investigated.

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 (MV2+). Conformation and anchoring of MV2+ 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.

Functional nanostructures of montmorillonite with conducting polyaniline

Abstract The present work describes the effect of montmorillonite (MMT) particles on the alignment of conducting polyaniline (PANI) chains in a PANI/MMT composite. The composite was prepared both as a powder, pressed into pellets, and as thin films deposited on glass surfaces. For comparison, pure PANI was also prepared in these two forms. A combination of X-ray powder diffraction analysis and molecular modelling confirmed the successful intercalation of the PANI into theMMT, while Raman spectroscopy confirmed the presence of the conducting form of PANI (i.e. the emeraldine salt) in all samples. Scanning electron microscopy, transmission electron microscopy and atomic force microscopy were used to study the morphologies of all samples. Conductivity measurements showed that the presence of the MMT particles in the PANI/MMT composites contributes to a significant increase in the electrical conductivity in comparison with the pure PANI samples. Moreover, in the pressed pellets the presence of theMMT particles led to an extremely high electrical anisotropy. TheUV-VIS spectroscopy results showed that the PANI/MMT thin film exhibited a selective transmittance in the range 450-650 nm; therefore, the PANI/MMT thin film is not only conductive, but also suitable for use in various optical applications.

Structure and properties of polyaniline/montmorillonite nanocomposites prepared under various conditions

Abstract Three different methods have been used for the preparation of polyaniline/montmorillonite nanocomposites: (i) two-step process: first intercalation of anilinium into Ca–montmorillonite structure followed with oxidisation; (ii) two-step process: first oxidisation with subsequent addition of Ca–montmorillonite aqueous suspension; (iii) one-step process: oxidisation and polymerisation in the presence of Ca–montmorillonite aqueous suspension. Structure and properties of samples have been investigated using combination of X-ray powder diffraction, Fourier transform infrared and Raman spectroscopy, elemental analysis and conductivity measurements in order to find the relationship between technology, structure and electrical properties. Results confirmed the crucial effect of the preparative procedure on polyaniline/montmorillonite composites.