V. G. Bekeshev

Mössbauer Spectroscopy of the Ferrocene-Containing Thermotropic Liquid Crystals

Abstract The 57Fe Mossbauer spectroscopy has been used to study the liquid crystalline disubstituted derivatives of ferrocene (FLCn). Characteristic Debye temperatures, order parameters, intramolecualar and lattice contributions to the nuclear vibrational anisotropy have been obtained for these compounds and 7% (weight) solution FLCIO in the nematic LC H8.

Oxidatively induced coupling of fluorenyl ligands in 9-methylfluorenyliron complexes

Abstract Oxidation of zwitterionic 9-methylfluorenyliron complexes [(η 6 -9- CH 3 C 13 H 8 )(η 5 - C 5 R 5 ) Fe ] ( R = H, ( I ) or CH 3 (II) by AgBF4 or (C5H5)2FeBF4 leads to binuclear dications {(μ-η 6 :η 6 -9,9′-( CH 3 ) 2 -9,9′- C 13 H 8 C 13 H 8 )[ Fe(C 5 R 5 )] 2 }( PF 6 ) 2 ( R = H ( III ) or CH 3 ( IV )) owing to coupling of two methylfluorenyl ligands at the 9 position. It was found that the presence of 9-methyl substituent in fluorenyl ligand plays an important role in determining the result of oxidation of I and II.

On the Limits of Sensitivity of PALS to Incorporated Free Volume Holes in Polymeric Membranes and Sorbents: Effect of sc -CO 2 in Polyhexafluoropropylene

Positron annihilation lifetime spectroscopy (PALS) is a recognized instrument for the studies of size-distribution of nanopores (intrinsic free volume holes FVH) in polymers, particularly membrane materials. The limits of this application in the case of “alien” pores, produced by swelling of poly (hexafluoro propylene) PHFP in the gas (CO2) in super-critical (sc-) state are discussed. The obtained conclusions are controlled by measurements of low temperature gas (N2) sorption (LTGS) and by comparison of the data with the results on permeation of various gases through the PHFP membrane. Attention is payed to relaxation with time of the newly created FVH in the PHFP membrane.

Mössbauer label and radiothermoluminescence methods for the study of low-temperature polymorphism and dynamic properties of metastable phases of thermotropic liquid crystals

The Mössbauer label and the radiothermoluminescence (RTL) methods were used for the study of low-temperature polymorphism of thermotropic liquid crystals (LC) possessing glassy and supercooled mesophases as well as solid metastable phases. The dynamic properties of unstable LC phases are also investigated. The activation energies for various types of molecular and fragmental movements in these mesophases are estimated from their RTL spectra. From Mössbauer spectra, the diffusional characteristics of different low-temperature mesophases are obtained.

Ferrocene Mesogens: Polymorphism, Molecular Properties and Temperature Stability

Abstract The Mossbauer spectroscopy, polarization microscopy, differential scanning calorimetry and X-ray photoemission spectroscopy were used to study of structure peculiarities, dynamical and orientational properties and thermal stability of ferrocene mesogens with general formula Fe(C5H4C(CH3)=N-N=CHC6H4COOC6H4OCnH2n+1) where n = 8, 10, 12. The obtained data were compared with those for nonmesomorphic derivatives of ferrocene and organic liquid crystals.

Metallomesogens: Structure and properties

The original investigations of ferrocene mesogens with general formula Fe(C5H4C(CH3)=N−N=CHC6H4COOC6H4OCnH2n+1J2 and their solutions in liquid crystalline solvents by Mossbauer spectroscopy as well as by calorimetry, thermomicroscopic and X-ray analysis are discussed. The data on electron, molecular and crystal structures, polymorphism and dynamical properties of these substences and frozen solutions are presented. For ferrocene mesogens and their solutions, aligned by external magnetic field, the values of order parameter and inter- and intramolecular contributions to the nuclear vibrational anisotropy of central metal atom are estimated.

Mössbauer spectroscopy of ferrocene-containing thermotropic liquid crystals

Abstract57Fe Mössbauer spectroscopy has been used to study some liquid crystalline disubstituted derivatives of ferrocene (FLCn). The characteristic Debye temperatures for these compounds were found to be in the range of 25–31 K. The order parameters, and intramolecular- and lattice-contributions to the nuclear vibrational anisotropy have been obtained from the analysis of the angular dependence of the Mössbauer parameters.

Nanoporosity of Polymer Membrane Materials and Sorbents According to Positron Annihilation and Low-Temperature Gas Sorption Data

Based on the experimental data obtained by the authors in a number of previous studies, the limits of applicability of positron annihilation lifetime spectroscopy (PALS) and low-temperature gas sorption (LTGS) to determination of nanoporosity (size distribution of nanopores in the range from a few fractions of a nanometer to 50 nm) in polymeric membrane materials and sorbents are discussed. It turns out that none of these methods is universal. The possibility of using each of them is determined by different factors, with the cases considered being finely divided polymer materials and the membranes per se cast from powders. It has been shown that the particle size factor is important for the applicability of LTGS. The possibility of using PALS depends on the concentration of nanopores of a given size.

A study of metal-containing products on the basis of polyphenylenesulphide☆

Abstract The interaction of molybdenum, tungsten, chromium and iron carbonyls with poly-1,4-phenylenesulphide was investigated. The structure of composites on the basis of Fe 3 (CO) 12 was studied in detail. It could be shown that chemical bonds between the metal and the polymeric ligand are not formed in any of the systems studied.