Thermotropic liquid crystalline compounds with lateral long-chain substituents (III). Molar volumina,viscosities, optical refractive indices and order parameters of 1,4-Bis-[4-n-octyloxybenzoyloxy]-2-n-alkylbenzenes

In the substance class of the general formula densities, thermal expansion coefficients, viscosities, optical refractive indices and the order parameters of a dissolved dye were measured in the isotropic and nematic states. The results are discussed briefly.     

Influence of lateral branches on the properties of liquid-crystalline 1,4-Bis-[4-n-hexylbenzoyloxy]-2-subst.-benzenes (I).: measurement of density,viscosity and optical anisotropy

8 compounds of the substance class of the 1,4-bis-[4-n-hexylbenzoyloxy]-2-subset.-benzenes and additionally 1,4-bis-[4-n-hexyleyclohexanoyloxy]-2-ethylbenzene were sythesized and density, viscosity and optical refractive indices were measured in the nematic and isotropic state. The lateral branching causes decrease of the melting and clearing temperatures, diminishing of the optical anisotropy and order parameter, but increase of the viscosity.     

EDA Complexes in Liquid Crystalline Mixed Phases of Novel Compounds with Lateral Dicyanoethenyl Substituents

We synthesized each four members of the new series All compounds are nematic. The dicyanoethenyl derivatives possess strong elecgtron acceptor properties. This is demonstrated by EDA complex formation in two binary systems in which induced smectic phases are lacking.     

New thermotropic cubic mesophases

1,2-Bis-[4-n-alkyloxybenzoyl]-hydrazines with the general formula possess smectic C phases and at lower temperatures additional optically isotropic phases. According to X-ray investigations these isotropic phases show cubic symmetry. The lattice units consist of aggregations with micellar dimensions. The substances were characterized by microscopic, dilatometric and calorimetric investigations. The new cubic mesophases do not exhibit complete miscibility with the “smectic D” phases.     

Thermotropic liquid crystalline compounds with lateral long-chain substituents (II).: Synthesis and liquid crystalline properties of 1,4-Bis [4-substituted-benzoyloxy]-2-n-alkylbenzenes

We synthesized 102 new 1,4-bis-[4-subst.-benzoyloxy]-2-n-alkylbenzenes of the general formula with R = alkyl, alkyloxy, alkanoyloxy, alkyloxycarbonyloxy and n = 0 to 16. Surprisingly all of the new compounds are liquid crystalline nematic. Thus it is proved that lateral long chain substituents are compatible with liquid crystalline properties.     

The polymorphism of some liquid crystalline 4′-n-alkyloxy-3′-nitro-biphenylcarboxylic acids

The substances of the homologous series with n = 6, 12, 14, 15, 16, 18 were investigated by calorimetry and microscopy. In the lower members exist nematic, smectic A and smectic C phases, in the homologs with n = 16 and 18 appear phases of the type smectic D with cubic structure. The kinetics of these phase transitions, in which smectic D is participating shows a strong dependence upon the experimental conditions. Supercooling, as well as, overheating effects were found. In the supercooled state we could detect for the first time smectic phases, which are metastable with respect to another liquid crystalline phase (S_D).     

OD interpretation of the crystal structure of lithium tellurite,Li2TeO3

The OD groupoid family of the structure of lithium tellurite, Li₂TeO₃, is characterized by the symbol: . The OD groupoid of the structure is deduced from the observed arrangement of points in reciprocal space, the symmetry of the intensity distribution and the systematic absences. The structure is built of OD layers of one kind. Any OD layer is idendical to a Li₂TeO₃ double sheet. The assumption of Folger that the structure is an OD structure has been found to be justified.     

Investigation of the Interaction of Quartz with Hydrogen under Supply of Mechanical Energy (II) Investigation by IR Spectroscopy

Infrared investigations demonstrate a chemical interaction of quartz in hydrogen atmosphere during mechanical activation: By means of the SiH stretching band the number of formed SiH-groups is estimated as a function of the period of activation. of activation. This number is more than one order of magnitude less than the total number of adsorbed molecules.     

Thermotropic Liquid Crystalline Compounds with Lateral Long Chain Substituents (VII). X-Ray Studies in 1,4-Bis-(4-n-oetyloxybenzyoloxy)-2-n-alkylbenzenes

X-ray studies in substances with the general formula in the nematic states were performed. The results prove the existence of cybotactic groups despite the fact that the branched substances do not show smectogenic properties. We propose a model for the packing of the molecules, which explains the influence of the lengths of the lateral branches on the structure of the cybotactic groups.     

OD Interpretation of Pyroxenes

The structures of pyroxenes are interpreted as OD structures consisting of layers. The symmetry relations of the idealized structures of “high pyroxenes”, consisting of only one kind of silicate sheets are described by the OD groupoid family: In this case the tetrahedral layers (OD layers) are identical with silicate sheets and the octahedral layers (OD layers) are identical with the chemical octahedral sheets, apart from the fact, that the O atoms are considered to belong partly to one and partly to the other idealized layer. In the idealized pyroxene structures, which are called in this paper “low pyroxenes”, every second silicate sheet is of lower symmetry. A silicate sheet of higher symmetry is considered as an OD layer, called tetrahedral layer. An OD layer of the other kind, called compound layer, consists of one silicate sheet of lower symmetry with an octahedral sheet attached to it on either side. With this definition of the two kinds of layers, the OD groupoid family has the following symbol: Polymorphism, disorder, twinning and parallel intergrowth are explained on this basis.     

Chiral SmC* liquid crystals obtained by mixing of SmC and cholesteric phase

The binary mixtures of the substance providing cholesteric phase exhibit a chiral SmC* phase for certain concentration and temperature range. This phase was verified to be ferroelectric. The temperature dependences of the spontaneous polarization and the coercive field were determined for three concentrations. The pitch of the helical structure is approximately indirectly proportional to the molar concentration of the cholesteric substance and varies from 3 μm to about 25 μm in the concentration range from 20 mol% to 5 mol% of the cholesteric substance. For the lower concentrations the sample is unwound in planar samples due to the surface anchoring. Two possible unwound planar configurations can be switched by electric field.     

The OD Structure of Dinitrosylcobalt Chloride, [Co(NO)2Cl]2

The OD groupoid family of the structure of dinitrosylcobalt chloride, [Co(NO)₂Cl]₂, is characterized by the symbol: The OD groupoid family of the structure is deduced from the observed arrangement of points in reciprocal space, the symmetry of the intensity distribution and the systematic absences. The structure is built of OD layers of one kind. The determination of the structure of the ordered orthorhombic form (MDO₂) has been determined from Weissenberg data obtained by JAGNER and VANNERBERG refined with OD full-matrix least-squares methods, based on a total of 150 reflections and anisotropic temperature coefficients. An R value of 0.13 has been obtained. The assumption of JAGNER that the structure is composed of dimers has been found to be justified.     

The precipitation of sparingly-soluble metal chromates from aqueous solution in the presence of chelating organic anions: Induction periods and nucleation rates

The precipitation of barium, zinc, lead, copper and silver chromates was studied in the presence of the chelating organic anions gluconate, tartrate, citrate, aspartate, glutamate and E.D.T. Aate. Generally, these chelators complex the metal cation and reduce the free metal cation and mean metal chromate concentrations in solution. The rates of nucleation with microcrystallite formation were then markedly reduced and the induction periods increased from below 1 sec to well above 100,000 sec with increasing chelator/cation concentration ratio; the experimental results were expressed by the relations; The coefficients F at any metal chromate concentration were related in turn to the stability constants of the metal-chelator complexes.     

Unique morphologies of zinc oxide synthesized by thermal decomposition and co‐precipitation routes: Ultraviolet absorption and luminescence characteristics

Two facile and efficient methods, to synthesize zinc oxide (ZnO) particles with different morphologies, have been reported here. Thermal decomposition route yielded micron sized irregular shaped ZnO particles. While co‐precipitation method rendered transparent flakes which then transformed to hexagonal discs with relatively more uniform size and shape. These hexagonal discs were further converted to the cone type morphology when hexamethylenetetramine was added in the precursor solution. However, spherical type ZnO nanoparticles were obtained by incorporating polyvinyl alcohol during co‐precipitation strategy. XRD confirmed the formation of wurtzite structure in all the samples. FTIR spectroscopy revealed the presence of ZnO characteristic peaks. Moreover, 3‐D directional growths and the presence of UV‐Vis broadband multi‐absorption peaks, and green to orange photoluminescence emissions confirmed the potential application of the synthesized ZnO particles in various piezoelectric and luminescence applications.

     

The structure of N-Pyrid-2-yl-iminotriphenylphosphorane,C23H19N2P

M_r = 353.9, monoclinic, P 2₁/c, a = 11.371(4), b = 11.391(5), c = 14.699(11) Å, β = = 97.78(2)⁰, Z = 4, V = 1888.6(6) ų, D_x = 1.28 Mgm⁻³, final R = 0.052 for 2360 independent reflections excluding those with |F₀| < 5 σ(F₀). Intensities were measured with an automatic diffractometer. The PN C- part of the molecule is nearly coplanar with the pyridinring (torsion angle 6.4°). The P atom and the N(2) atom of the pyridinring overlap with their van der Waals spheres and have nearly the position with the maximum of steric hindrance. This conformation of the molecule is the consequence of a conjugation between the Ph₃P=N-group and the N-standing pyridine ring as well as of an attraction between the P atom and the N(2) atom.     

Reactivity of CCl4 plasma against SiO2 surfaces

SiO₂ is etched considerably by a CCl₄ plasma at surface power densities of about 0.3 W cm⁻². This etching process is investigated by the SiCl₄ formation with aid of mass spectroscopy where final products of the etching process and the extracted ions were studied in dependence on time in a closed plasma volume. The primary step of the etching process is the activation of SiO₂ by the plasma involving breaking of siloxan bridges. The overall mechanism of the SiO₂ etching by the CCl₄ plasma is proposed in form of The rate limiting constants are k₀ and k₃. The SiCl₄ formation is decreased or inhibited by an admixture of Cl₂, H₂, O₂ or CO to the CCl₄ plasma. CCl₄-Plasmen führen zu einem Ätzangriff an SiO₂-Oberflächen. Dieser Ätzprozeß ist bei Leistungsdichten an der zu ätzenden Oberfläche von > 0,3 W cm⁻² deutlich über eine SiCl₄-Bildung nachweisbar. Der Primärschritt ist eine Aktivierung der SiO₂-Oberfläche durch das Plasma, die zu Bindungsbrüchen der Siloxanbrücken führt.     

The structure of N-Pyrid-4-yl-iminotriphenylphosphorane,C23H19N2P

M_r = 353.9, monoclinic, P 2₁/c, a = 11.248(2), b = 11.323(2), c = 14.845(4) Å, β = = 95.87(2)⁰, Z = 4, V = 1880.8(3) ų, D_x = 1.28 Mgm⁻³, final R = 0.049 for 1995 independent reflections excluding those with |F₀| < 5 σ(F₀). Intensities were measured with an automatic diffractometer. The PN C-group of the molecule is nearly coplanar with the pyridine ring (dihedral angle 4.1°). The P atom and the C(2) atom of the pyridine ring overlap with their van der Waals spheres and have nearly the position with the maximum of steric hindrance. This conformation is the consequence of a conjugation between the Ph₃PN group and the N-standing pyridine ring as well as of an attraction between the P atom and the C(2) atom. A similar conformation has been observed in the molecule of N-pyrid-2-yliminotriphenylphosphorane.     

Crystal growth,crystal structure and pyroelectric properties of the polar hexagonal antimony tartrates MII[Sb2(C4H2O6)2]·2H2O (MII = Ca,Sr, Pb)

Single crystal growth of lead antimony tartrate dihydrate, Pb[Sb₂((+)C₄H₂O₆)₂]·2H₂O, was successfully performed. The determined polar hexagonal crystal structure is isomorphous to the corresponding calcium and strontium antimony tartrates dihydrates. New results of crystal growth and the redetermination of the crystal structures of the nonlinear optical crystal Sr[Sb₂((+)C₄H₂O₆)₂]·2H₂O and its calcium analogue are reported, together with investigations of the thermal stability and the pyroelectric properties of these polar crystals.

     

Two parameter kinetic equation of size dependent crystal growth

The previously proposed hyperbolic, three parameter empirical model of size dependent crystal growth can be reduced to the two parameter one of the form This simplification reduces dimension of the least squares correlation of crystal size distribution in MSMPR crystallizer thus saving amount of calculations with a negligible loss of accuracy estimated by means of the mean residual square deviation. The additional advantage is that a differential balance of crystal number in MSMPR crystallizer can be solved analytically for the simplest case of the exponential function of secondary nuclei size distribution. Correlations for single experiment with ammonium alum are presented.     

The effect of B2O3 on the solubility of (YSmLuCa)3(FeGe)5O12 garnet in PbO-B2O3 flux

The paper deals with the solubility of (YSmLuCa)₃ (FeGe)₅O₁₂ garnet in PbO—B₂O₃ flux. An anionic model explaining the effect of B₂O₃ on the solubility of rare earth garnet is suggested. This model is based on the assumption that PbO in the melted mixture of PbO, B₂O₃, Fe₂O₃, R₂O₃, CaO, GeO₂ dissociates into Pb²⁺ and O²⁻. The oxygen anions react with the other oxides under the formation of BO₃³⁻, FeO₃³⁻, RO₆⁹⁻, CaO₂²⁻ and GeO₃²⁻ anions, until the equilibrium is established. The garnet is dissociated into the anions mentioned above. The validity of the model is verified by an agreement of the experimentally determined saturation temperatures of the melts for LPE of garnet layers with the Arrhenius-type expression of the solubility product of garnet where x_i denotes the equilibrium concentrations of the anions in the melt and x° is the Ge content of the garnet film.