Spectroscopic studies of Langmuir-Blodgett films of 3,4,9,10-tetra(heptyloxycarbonyl)perylene and its mixtures with a liquid crystal

Langmuir (L) and Langmuir-Blodgett (LB) films of 3,4,9,10-tetra(heptyloxycarbonyl)perylene and its binary mixtures with 4-octyl-4'-cyanobiphenyl (8CB) and 4-pentyl-4'-cyano-p-terphenyl (5CT) have been studied. On the basis of the surface pressure-mean molecular area isotherms of L films, the alignment of the molecules on the air-water interface has been estimated. The L films were transferred onto quartz plates at surface pressures below the collapse point. The absorption and fluorescence spectra of LB films, obtained using unpolarized and linearly polarized light, were recorded. The results obtained have led to conclusions on the arrangement of the dye and liquid crystal molecules on the air-solid substrate interface. The fluorescence spectra revealed the formation of excited dimers in LB films.     

A novel type of tautomerism in cyclic silylamides

N-Acetyltetramethylcyclodisiloxane, (I), co-exists in equilibrium with pentamethyldisiladioxazine, (II), in a novel type of tautomerism.     

Photomechanical vibration of thin crystals of polar semiconductors

It was found that thin crystals of polar (non-centrosymmetric) semiconductors constitute a new type of photo-sensitive system in which incident illumination is converted into mechanical energy: thus, illumination-induced elastic deformation (bending) was observed on thin (00.1) CdS and (111) GaAs crystals; furthermore, by employing chopped light the crystals were excited to their resonant vibration (photomechanical vibration); the dependence of the amplitude of this vibration on the energy of the incident radiation was found to be similar to the dependence of the surface photovoltage on the energy of the incident radiation (surface photovoltage spectrum). The present findings are consistent with a model based on light-induced modulation of the piezoelectric surface stresses.     

Locally conserved currents linearly dependent on the energy-momentum tensor and the polynomial in the position variables

In this note we are considering a symmetrical locally conserved energy-momentum tensor, whose trace vanishes. We show that there are no other combinations of the position variables x and the energy-momentum tensor, whose divergence vanishes except the well-known currents of translations, four-dimensional Lorentz rotations as well as con- formal and dilatational transformations.     

Simultaneous determination of light and heavy lanthanides in their mixture with methylthymol blue as indicator

A method of simultaneous determination of heavy and light lanthanides has been described. In the first stage, the total amount of rare earth elements is determined (complexometrically with EDTA as a titrant and MTB as an indicator, pH = 5.5). Then, on the basis of the proportional relationship between absorbance and molar ratio of the system, concentration of each component is calculated (using the measured absorbance of the system and “the absorbance of the standard” taken from the standard calibration curves). The applicability of the method is limited by r.e.e. concentration equal to 3 × 10^?5M. In the case when the content of one of the metals amounts to at least 15% of their sum, the relative error of determination does not exceed 2%.Results of the determination for selected pairs of lanthanides are presented together with a statistical estimation of errors.     

Ni(II)/N,N-dimethylglycine complex equilibrium study

The complex formation of Ni(II) withN,N-dimethyl-glycine in water and in water-methanol has been studied by computer analysis of potentiometric data.

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Gleichgewichtsuntersuchungen der Komplexbildung von Ni(II) mitN,N-Dimethylglycin (Kurze Mitteilung)

Zusammenfassung Anhand der Computer-Analyse von potentiometrischen Daten wurden die Bildungsgleichgewichte von Nickel(II)-Komplexen mitN,N-Dimethylglycin in Wasser und Wasser — Methanol untersucht.

     

Pillared montmorillonites modified with silver

Alumina, zirconia and titania pillared montmorillonites additionally modified with silver were tested as catalysts of NO reduction with NH₃ or C₂H₄. Ammonia was much more effective reducer of NO than ethylene. The silver containing TiO₂-pillared clay has been found to be the most active catalyst for NO reduction both with NH₃ or C₂H₄. Oxidation of the reducing agents by oxygen limited the NO conversion in the high temperature region. The ammonia and nitric oxide adsorption sites were studied by the temperature programmed desorption methods (TPD). This revised version was published online in July 2006 with corrections to the Cover Date.     

Tensammetry with accumulation on the hanging mercury drop electrode : Part 5. The behaviour of mixtures of oxyethylated alcohols

The behaviour of the following mixtures of polydispersed oxyethylated alcohols having a well-defined n-alkyl radical was investigated: 18-14/6-14, 18-14/10-14, 18-14/18-10, 18-14/18-6, 18-6/18-10, 6-14/10-14 and 18-6/18-10/18-14 (the first number denotes the number of carbon atoms in the n-alkyl chain, and the second is the number of oxyethylene subunits). The influence of preconcentration potential in the range more negative than - 1.0 V vs. SCE is described in detail. The results are compared with the behaviour of model mixtures of poly(ethylene glycols). The surfactant mixtures 18-14/6-14 and 18-14/10-14 behave similarly to a model mixture of components having sufficiently different properties. Separate peaks for both components appear on the tensammetric curves of the mixtures, but only at certain preconcentration potentials are the peak heights similar to the peak heights for the individual components alone. The behaviour of the 18-14, 18-10 and 18-6 mixtures, in alt combinations, depends strongly on whether premicellar (associated) forms are present in the solution. These premicellar forms are indicated by a common very narrow peak on the tensammetric curves. If the monomeric forms predominate (i.e., at low-total surfactant concentrations) the peak heights for the mixtures are approximately additive after preconcentration at a suitable potential. If premicellar forms predominate (as at total concentrations > 0.1 mg l^?1), the behaviour of the mixtures is a result of competition between the monomeric and premicellar forms in the adsorption process. This behaviour approximates the behaviour of a mixture consisting of sufficiently different components; monomeric forms behave like the first component, and premicellar forms like the second component of the model mixture. For the surfactant mixture 18-14/18-10, which behaves additively under certain conditions, it is possible to determine the total concentration within the range 10-35μgl^?1. The 6-14/10-14 mixture forms a single nonadditive peak.     

Effect of composition and gelation conditions on structural changes accompanying the gelation of PAN,PVA and gelatin solutions

Summary For three types of polymer-solvent systems: polyacrylonitrile in dimethylformamide, polyvinyl alcohol in water and gelatin in water the isothermal gelation process was followed with viscometry, light scattering and X-ray diffraction techniques. Effects of thermal history (quenching, melting) and solvent composition were investigated. It was found that the variation of structure as revealed by these methods (molecular aggregation, crystallization etc.) is not specific for the gelation itself but associated with some side-processes which result from retarded phase separation. The molecular mechanism of “pure gelation” proceeding at unchanged supramolecular structure is discussed.

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Zusammenfassung Für drei Systeme Polymer/L?sungsmittel, n?mlich für Polyacrylnitril in Dimethylformamid, für Polyvinylalkohol in Wasser und für Gelatine in Wasser, wurde die isotherme Gelierung viskosimetrisch, mit Lichtstreuung und mit R?ntgenbeugung beobachtet. Die Wirkungen der thermischen Vorgeschichte (Abschrecken, Schmelzen) und der L?sungsmittelzusammensetzung wurden untersucht. Es ergab sich, da? die ?nderung der Struktur, wie sie mit diesen Methoden aufgedeckt wurde (Molekularaggregation, Kristallisation usw.) nicht spezifisch für die Gelatinierung ist, sondern mit einigen Nebenprozessen, die aus verz?gerter Phasentrennung resultieren, verknüpft ist. Der molekulare Mechanismus einer reinen Gelatinierung, der bei unver?nderter Supermolekularstruktur stattfindet, wird diskutiert.

     

Electrochemically inactive organic substance influence on peak height in anodic stripping voltammetry

A simplified method was proposed for calculation of changes of peak height (i) vs. deposition time (t_e) in the presence of a surfactant acting only at the deposition stage. The simplification was based on the assumption that the deposition current has a constant value until time t₁ when it decreases abruptly to a lower level. Hence the dependency of the peak height on the deposition time can be written:i=β₀t₁+β₁(t_e?t₁) Limiting cases were discussed: t₁→0 and β₁→1 leading to three types of i vs. t_e relation. The experimental evaluation was carried out for Pb(II), Cu(II) and Cd(II) in the presence of various polyethyleneglycols. All three types of curves were obtained in the experiments, as well as some which did not fit the simplified theory.