Electrochemical production, characterization, and application of MWCNTs

The subject of this study is production of carbon nanotubes (CNTs) using an original procedure of reduction of lithium molten salts onto graphite cathode; their structural characterization and application as support material for electrocatalysts aimed for hydrogen evolution. As-produced CNTs were characterized by means of scanning and transmission electron microscopy (SEM and TEM), Raman spectroscopy, and thermogravimetric and differential thermal analysis (DTA). SEM and TEM images have shown that nanotubes are mostly of curved shape with length of 1–20 μm and diameter of 20–40 nm. Raman peaks indicate that the crystallinity of produced nanotubes is rather low. The obtained results suggest that formed product contains up to 80 % multiwalled carbon nanotubes (MWCNTs), while the rest being non-reacted graphite and fullerenes. DTA curves show that combustion process of the nanotubes takes place in two stages, i.e., at 450 and 720 °C. At the lower temperature, combustion of MWCNTs occurs, while at higher one, fullerenes and non-reacted graphite particles burn. As-produced MWCNTs were used as electrocatalyst’s support materials and their performance was compared with that of traditional carbon support material Vulcan XC-72. MWNTs have shown almost twice higher real surface area, and electrocatalyst deposited on them showed better catalytic activity than corresponding one deposited on Vulcan XC-72.     

Polarization reflection holographic gratings in azobenzene-containing gelatine films

We have written polarization reflection holograms in an azobenzene-containing material. Two waves with circular polarization were used to record the gratings; the light resulting from their overlap induces chirality in the samples. The holographic reflection of the polarization gratings has the properties of Bragg reflection in cholesteric liquid crystals.     

Photoinduced dichroism and birefringence in films of Mordant Pure Yellow/poly(vinyl alcohol): simultaneous real-time investigations at two wavelengths

Photoinduced anisotropy in films of azo-dye Mordant Pure Yellow (MPY) dissolved in a polyvinyl alcohol matrix, is investigated. The photodichroism and photoinduced birefringence are measured in real time for two wavelengths, 488 nm (in the absorption band) and 633 nm (outside it), on excitation with an Ar⁺ laser beam. It is shown that strong dichroism is induced without changing the average optical density of the film, and the kinetic curves of the birefringence and the dichroism are substantially different. The conclusion is made that the photoprocesses of the dye molecules cause a reconstruction of the matrix.     

Compressing thin spheres in the complement of a link

Let L be a link in S³ that is in thin position but not in bridge position and let P be a thin level sphere with compressing disk D. We introduce the idea of alternating level spheres for D and show that all such spheres are thin and their widths are monotone decreasing. This allows us to generalize a result of Wu by giving a bound on the number of disjoint irreducible compressing disks P can have in terms of the width of P, including identifying thin spheres with unique compressing disks. We also give conditions under which P must be incompressible on some side or be weakly incompressible. In particular we show that the thin level sphere of second lowest width is weakly incompressible. If P is strongly compressible we describe how a pair of compressing disks must lie relative to the link.     

Bifocal-polarization holographic lens

We present a holographic lens with novel features recorded in an azopolymer film. Two holographic modulations, bulk birefringence and surface relief, are induced in the medium at the same time. The resultant holographic element has two focal planes, and the polarization of light in the focal points depends on the polarization of the incident light. Applications of this device for writing-reading information in two planes simultaneously or separately are described.     

High-sensitivity material with reversible photo-induced anisotropy

A new high-sensitivity material with reversible photo-induced anisotropy, suitable for real-time recording, is investigated. The material (methyl-red dye introduced in a polymer layer) requires low recording intensities (tens of mW cm^-2) and possesses excellent reusability.     

Photochromism and dynamic holographic recording in a rigid solution of fluorescein

An investigation was made of the spectra, the kinetics of induction and thermal decay and the dichroism of the photoinduced triplet absorption band in a rigid solution of fluorescein in orthoboric acid. Dynamic holographic recording was possible on this material. An experimental study was conducted into the polarizing properties of the volume transmission holograms. The experiments on four-wave mixing with continous laser light revealed a very high resolution for this rigid solution when used as a medium for optical recording. As a result of the investigations, some possible applications of the rigid solution of fluorescein are pointed out.     

Electron trapping and untrapping during the dark decay of flash-produced KC1 F′ and F′ > A(Na) bands between 290–350°K

Both the thermal lifetimes of the F′(F′_A) centers and the ratios of the electron trapping cross-sections of (F_A) to α(α_A) centers were derived from the decay kinetics of flash-produced F′(F′_A) bands. In particular, the ratios dropped steeply with the temperature possibly due to a thermally activated de-excitation following excited state pre-trapping of the electron by the anion vacancy.