Synthesis and characterization of new chiral liquid crystalline polyacrylates from L-isoleucine

The synthesis of chiral side chain liquid crystalline polyacrylates with a two-stereogenic centre from L-alpha-aminoacid is described. The chiral tail is 2-chloroalcohol obtained from L-isoleucine and the spacer group has either four or eleven methylene units. The mesogenic moiety is derived from phenyl benzoate. The stereochemistry of the key intermediate (2 S ,3 S )-(+)-4- [1-(2-chloro-3-methyl)pentyloxy]phenyl benzoate ( 6 ) obtained by a Mitsunobu reaction was established by single crystal X-ray analysis. This result indicates that the nucleophilic displacement of chiral diazonium salts proceeds with overall retention of configuration. The liquid crystalline behaviour of polyacrylates P 13 and P 14 was investigated by DSC, optical microscopy, small angle X-ray scattering and depolarized light scattering. The polyacrylate P 13 , with eleven methylene units in the spacer, exhibits a chiral smectic A phase whereas the polyacrylate P 14 , with a spacer containing four methylene units, displays a chiral nematic phase.     

Charge storage in 40/60 TiFe alloy electrodes

Charge storage in 40/60 TiFe alloy has been investigated using electrode fabrication powder material, either of true alloy or of alloy precursor grades. The true alloy activated very reluctantly in that its maximum charge (i.e., hydrogen) capacity remained below 100 mA h g^{– 1}. In contrast, the alloy precursor could be activated to an intrinsic capacity of ~300 mA h g^–1. Charge storage of the 40/60 TiFe alloy precursor was certainly affected by the redox reactions of surface Fe, but a large amount was stored as hydrogen absorbed by the material, as indicated by a dialometric test and the poison effect. X-ray and EDAX analyses of the two materials can account for their differing abilities to store charge. Electronic Publication     

A Mössbauer spectroscopy study of antiferromagnetic iron arachidate Langmuir-Blodgett films

Langmuir-Blodgett multilayers of ferric arachidate (abbreviated: FeA) on silicon wafers have been investigated by means of conversion electron Mössbauer spectroscopy (CEMS) and absorption Mössbauer spectroscopy at different temperatures between room temperature and 4.2 K, without and with external magnetic fields up to 5 T. The films show a quasicrystalline structure with ac-axis orientation perpendicular to the plane and a random distribution of orientations in the plane of the films. All Mössbauer spectra show Fe³⁺. At low temperatures, antiferromagnetic ordering has been observed. The lines in both the room temperature and the low-temperature spectra are significantly broadened, which is due to a distribution of electric field gradients and hyperfine fields. The reason for this is a slightly disordered iron environment. The orientation and the distribution function of the internal magnetic fields have been determined.     

Functions of Bounded Variation¶and Rearrangements

The action of the symmetric rearrangement of functions of bounded variation is investigated. In particular, pointwise regularizing effects are established. Pólya-Szeg? type inequalities, with a characterization of equality cases, are also proved.     

EFG determination in magnetic field oriented powders of YBa2(Cu1−x 57Fe x )3O7−y superconductors: A test of existing models

YBa₂(Cu_1-x ⁵⁷Fe _x )₃O_7–y powder samples withx=0.02 and 0.03 were uniaxiallyc-aligned in epoxy in a magnetic field of 7.5 T. An X-ray map of the distribution of the orientation of the crystallographicc-axes of the individual crystallites was determined.⁵⁷Fe Mössbauer spectra were recorded at room temperature as a function of the angle between the texture axis and the observation direction. Different sets of EFG parameters were selected from the literature and the fit constraints were equally set for all. Using a model of the measured texture function and accounting for polarization-dependent blackness effects, a simultaneous fit of the Mössbauer spectra results in minimum ² for the EFG set determined previously from CEMS data on this films.On leave from: Institute for Low Temperature Physics and Engineering, Ukr. Acad. Sci., Kharkov, Ukraine.