Evaluation of smectic biphenylcarboxylate ester liquid-crystalline polysiloxane stationary phases for capillary column gas chromatography

Mesomorphic biphenylcarboxylate esters were coupled via flexible aliphatic hydrocarbon spacers to a polysiloxane backbone. The influence of spacer length, percent mesomorphic substitution, and crosslinking of the stationary phase on liquid-crystalline transition temperatures and on chromatographic performance was investigated. Unique selectivity and good efficiency over a wide temperature range for gum and cross-linked liquid-crystalline phases were demonstrated by the separation of various isomeric polycyclic aromatic compounds.     

Rietveld Analysis of a High Pressure Modification of Monocalcium Oxogallate (CaGa2O4)

A high‐pressure modification of monocalcium gallate (CaGa₂O₄) has been prepared in a piston‐cylinder apparatus at 700 °C and 4.0 GPa. The compound is orthorhombic (space group Pnam, a = 9.12476(15) Å, b = 10.56093(18) Å, c = 2.98547(4) Å, V = 287.70(1) ų, Z = 4, D_calc = 5.62 g/cm³) and belongs to the CaFe₂O₄‐type structure family. The structure was refined by the Rietveld method using laboratory X‐ray powder diffraction data. Two crystallographically independent GaO₆‐octahedra forming edge‐sharing double chains can be distinguished. The shared edges exhibit a considerable shortening. The chains are running parallel to the c‐axis and are linked by corner‐sharing. They enclose tunnels in which the calcium atoms are located for charge compensation. Each calcium cation has eight nearest oxygen neighbors. The coordination environment can be described as a bicapped trigonal prism.     

An investigation of the changes in column efficiency accompanying the oxidation of apolar gas chromatographic stationary phases

Summary The effect of on-column oxidation upon the efficiency of apolar gas chromatographic columns is investigated. With an unsaturated hydrocarbon liquid phase and air as carrier gas dramatic changes of column efficiency are observed. Evidence is presented that suggests that this catastrophic deterioration of column performance is due to the oxidative crosslinking of the liquid phase molecules.     

Characterization of silicone phases by alkaline hydrolysis and CGC analysis

A simple way to elucidate the functional group substitution on silicone chains is presented. The polymer is decomposed into its monomers by alkaline hydrolysis. These monomers are converted into trimethylsilyl derivatives, which are then analyzed and identified by capillary gas chromatography/mass spectrometry.     

Dielectric properties of a highly polar liquid crystalline material showing various types of layered structures

Liquid crystal compound N-(4-n-pentyloxybenzalidene) 4′-n-pentylaniline is very interesting because of its rich phase variant, i.e. nematic, smectic A, smectic C, smectic F and smectic G phases. In the present work, temperature- and frequency-dependent dielectric studies on this compound in the homeotropic and planar orientation of molecules have been carried out in the frequency range of 1 Hz–10 MHz. The compound shows negative dielectric anisotropy (i.e. Δε < 0). Dielectric studies have shown three relaxation modes of different origin in various phases of the material. Relaxation frequencies of the observed modes follow Arrhenius behaviour. The relaxation due to interfacial polarisation, i.e. Maxwell–Wagner–Sillars effect has been observed in the nematic and isotropic phases. A relaxation mode due to the fluctuation of molecular tilt resembling the soft mode has been detected in the smectic A phase with pre- and post-transitional effects. Another mode due to the fluctuation of molecules about their short axes has been detected in the nematic and smectic A, C, F and G phases. Activation energies and ionic conductivity of these phases have also been determined.     

Double gyroid structures made of asymmetric dimers

Gyroid cubic phases are interesting for both scientists and engineers due to possible applications in electronic devices. New series of dimeric molecules, despite their flexible molecular structure, can display double gyroid cubic phase with Ia3d symmetry and lattice parameter corresponding to double molecular length. The cubic phase is structurally related to columnar phase and both phases often coexist in the same temperature window. Apparently, for studied compounds stronger molecular asymmetry promotes cubic structure. Interestingly, for the examined compounds the transition between two isotropic liquids was observed.     

Lithium Ion Mobility in Lithium Phosphidosilicates: Crystal Structure, 7Li, 29Si,and 31P MAS NMR Spectroscopy,and Impedance Spectroscopy of Li8SiP4 and Li2SiP2

The need to improve electrodes and Li‐ion conducting materials for rechargeable all‐solid‐state batteries has drawn enhanced attention to the investigation of lithium‐rich compounds. The study of the ternary system Li‐Si‐P revealed a series of new compounds, two of which, Li₈SiP₄ and Li₂SiP₂, are presented. Both phases represent members of a new family of Li ion conductors that display Li ion conductivity in the range from 1.15(7)×10^?6 Scm^?1 at 0 °C to 1.2(2)×10^?4 Scm^?1 at 75 °C (Li₈SiP₄) and from 6.1(7)×10^?8 Scm^?1 at 0 °C to 6(1)×10^?6 Scm^?1 at 75 °C (Li₂SiP₂), as determined by impedance measurements. Temperature‐dependent solid‐state ⁷Li NMR spectroscopy revealed low activation energies of about 36 kJ mol^?1 for Li₈SiP₄ and about 47 kJ mol^?1 for Li₂SiP₂. Both compounds were structurally characterized by X‐ray diffraction analysis (single crystal and powder methods) and by ⁷Li, ²⁹Si, and ³¹P MAS NMR spectroscopy. Both phases consist of tetrahedral SiP₄ anions and Li counterions. Li₈SiP₄ contains isolated SiP₄ units surrounded by Li atoms, while Li₂SiP₂ comprises a three‐dimensional network based on corner‐sharing SiP₄ tetrahedra, with the Li ions located in cavities and channels.     

Liquid‐Crystalline Properties of trans‐A2B2‐Porphyrins with Extended π‐Electron Systems

Incorporation of four trialkoxyphenyl substituents combined with extending the π‐conjugated system has allowed porphyrins to display liquid‐crystalline columnar phases at room temperature. 2D and 3D columnar structures were observed as well as a biaxial smectic phase.