Structural and dielectric investigations of a binary system of a bi-swallow-tailed and a terminally-polar compound

Induced smectic A phases in binary mixtures of a bi-swallow-tailed component and a second component are described as 'filled smectic A phases', since the second rod-like component is considered to occupy spaces between the terminal branches of the bi-swallow-tailed molecules. A new system of this kind is now described where the second rod-like component has a terminal dipole, thereby enabling dielectric studies of the mixtures. These measurements coupled with calorimetric and X-ray measurements give information about the packing and dynamics of the mixed phases.     

Solidification-induced and shear-induced band texture in thermotropic liquid crystalline polymer films

Two phase diagrams of a six-ring double-swallow-tailed compound are presented where the mixing components involve electron-acceptor compounds. In the mixed phase region, nematic, smectic A and C, cubic and columnar phases are induced. In this way transitions between lamellar, cubic and columnar phases can be realized by variation of the con- centration. The mesophases occurring in these systems have been characterized by X-ray investigations.     

Structures, properties and miscibility behaviour of liquid crystalline polycatenar tetrone derivatives

The tetrones represent an interesting new mesogenic building block. The results of this study show that they can be incorporated into a variety of mesophases. A smectic phase was observed in the polycatenar compound with four terminal chains as expected. The phase exhibits a tilted structure (S_c phase) to prevent void formation. The compound with six pendant chains forms a columnar phase. In spite of their structural similarity, the tetrones studied tended not to be completely miscible. However, complete miscibility with a semi-discoid phenylhydrazone was observed. When this hydrazone, which forms a columnar 'D_ho phase', was mixed with tetrone which forms a columnar 'D_hd phase' a columnar hexagonal phase was produced with enhanced stability. We believe that the stability enhancement derives from a charge transfer interaction between the tetrone and the phenylhydrazone.     

13C-NMR-spektroskopische untersuchung der tricarbonyl(1,2,3,4,5,2′-η-ethylcyclopentadien-1,2′-diyl)- komplexe des molybdäns und wolframs. deformierte σ-alkyl-π-cyclopentadienyl-metall-komplexe

Reactions of dialkylzinc compounds ZnR₂ (R  Me, Et) with pyrogallol (PG) have been carried out.The reaction products obtained with mole ratios of reactants 3/1 2/1 and 1/1, respectively, were characterized by means of IR, ¹H NMR spectroscopy, elemental analysis and cryometry.The product formed from ZnR₂/PG 2/1 (the best known catalytic system for the alternating CO₂/propylene oxide copolymerization) was found to be 1,3,2-benzodioxazincol-4-alkylzincolate.     

Sulphur ligated siamese twin mesogens

The synthesis of 3,3'-sulphinyl-bis-[alkyl 4-(4-substituted benzoyloxy)-benzoates] and 3,3'-sulphonyl-bis-[alkyl 4-(4-substituent-benzoyloxy)-benzoates] is described. These new nematic compounds are of the ligated siamese twin type. By microscopy and DSC calorimetry the thermal behaviour was investigated. Many of the new compounds transform on quenching to the glassy nematic state with glass temperatures above room temperature. Above the glass temperature the substances behave like highly viscous but ordinary nematics. The substances may be used for the construction of new thermo-electrooptic displays. By means of dielectric and X-ray investigations we were able to show that the two halves of the twin molecules are in an antiparallel orientation in the nematic state. In mixtures of the new compounds with rod-like nematics reentrant nematic behaviour was observed.     

Strukturbildung von homologen wasserfreien Lecithinen in Abhängigkeit von Temperatur und Kristallisationsbedingungen

The influence of temperature and crystallization of homologous lecithins on the phase transition was studied by X-ray diffraction. The different conditions of crystallization effect various structures. The structural differences between various samples of dimyristoyl-phosphatidyl-choline, di-palmitoyl-phosphatidyl-choline and di-stearoyl-phosphatidyl-choline were discussed and their lattice parameters compared. The results show that the polymorphism of the lecithins are depended on the chain length and the conditions of crystallization.     

The Cayley Method and the Inverse Eigenvalue Problem for Toeplitz Matrices

Despite the fact that symmetric Toeplitz matrices can have arbitrary eigenvalues, the numerical construction of such a matrix having prescribed eigenvalues remains to be a challenge. A two-step method using the continuation idea is proposed in this paper. The first step constructs a centro-symmetric Jacobi matrix with the prescribed eigenvalues in finitely many steps. The second step uses the Cayley transform to integrate flows in the linear subspace of skew-symmetric and centro-symmetric matrices. No special geometric integrators are needed. The convergence analysis is illustrated for the case of n = 3. Numerical examples are presented.