The N,N'-bis[4-(4-n-alkyloxybenzoyloxy)benzylidene]phenylene-1,3-diamines: mesophase behaviour and physical properties

A homologous series of banana-shaped compounds (n =1-12) is described. The short-chain derivatives exhibit a B₆ phase, while B₆/B₁ dimorphism is found for the pentyloxy and hexyloxy homologues. The B₁ phase of the compounds having longer alkyloxy chains is changed to a B₂ phase for the compounds with n =11 and 12. The phase characterization was performed using their optical textures and by means of X-ray investigations. Transition enthalpies were measured using DSC. In addition, density measurements were performed on one selected homologue. The compound n =8 exhibiting a B₁ phase was investigated also by high-pressure DTA.     

Analysis of special surfactants by comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry

Multidimensional gas-chromatographic analyses of olesochemically based nonionic, anionic and several cationic surfactants in industrial cleaners are demonstrated. Comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry allows the simultaneous determination of fatty alcohols, fatty alcohol sulphates and alkyl polyglucosides. In addition, the determination of fatty alcohol ethoxylates up to C₁₀EO₈ (highest degree of ethoxylation) and C₁₈EO₅ (longest C-chain at an ethoxylation degree of five) and the analysis of fatty alcohol alkoxylates that contain ethoxy (EO) and propoxy (PO) groups could be realized. Because of decomposition in the injector and a weak EI-fragmentation, cationic surfactants such as alkyl benzyl dimethyl ammonium chloride could also be identified by their characteristic fragments. Thermogravimetric analyses confirmed that the temperature in a normal GC injector is not high enough to cause thermal decomposition of esterquats. However, we could demonstrate that a modified silylation procedure forms decomposition products of esterquats in the GC injector which are detectable by GC × GC–(TOF)MS and allows the identification of such GC-atypical analytes.     

On the molecular and mesophase structures of disc-like tetrapalladium liquid crystals

Various members of two series of μ-halogeno-bridged tetrapalladium mesogens each with twelve dodecyloxy chains, but differing in the size of their large disc-like macroheterocyclic cores, 1 a-e and 2a-c, as well as one new short-chained homologue (1 c') of one of the series, as a model compound for single crystal X-ray studies, are presented. Our results on that model compound again unambiguously confirm earlier statements about the unique molecular structure of the core of these flat tetrapalladium complexes. The properties of all thermomesogenic compounds have been studied by differential scanning calorimetry, polarizing microscopy, and also by X-ray diffraction; the latter method reveals an oblique arrangement of disordered columns in most of the mesophases exhibited by the members of both series 1 and 2.     

Star-like discotic liquid crystals

The game of molecular engineering of liquid crystalline systems via a combination of molecular architecture and functionalization of mesogens has opened interesting perspectives in the field of liquid crystals. Here we report on the synthesis and characterization of star-like heptameric triphenylenes. The discotic subunits in these molecules have been arranged in a hexagonal fashion around a central discotic core, thus leading to a new type of molecular arrangement for discotic liquid crystals. These oligomers do not crystallize and combine a well-defined structure with a discotic polymer-like processing.     

Mesomorphic properties and magnetic behaviour of di-(5-substituted-salicylidene)ethylenediaminato cobalt(II) complexes

The result of optical X-ray, DSC and magnetic susceptibility studies of new Co(II) metallomesogens are reported. The di-(5-substituted-salicylidene)ethylenediaminato cobalt(II) complexes exhibit broad range S_a phases. A comparison with corresponding copper(II) and nickel(II) complexes leads to conclusions about how the properties are influenced by the metal atom. Cobalt(II) complexes of this kind form different modifications which are either active or inactive against oxygen. The conversion process (inactive-active) is monitored by time dependent X-ray diffractometric measurements.     

Infrarot-spektralphotometrische Bestimmung der ?freien? Silanolgruppen in pyrogenen Kiesels?uren

Zusammenfassung Die technischen Eigenschaften pyrogener Kieselsäuren werden entscheidend vom Gehalt an »freien« Silanolgruppen mitbestimmt. Die IR-Absorption dieser Gruppen in CCl₄ gehört zu einer Bande bei 3700 cm^–1. Es wurde festgestellt, daß die maximale Extinktion in CCl₄ unter bestimmten Bedingungen unabhängig von der Anzahl ebenfalls vorhandener »gebundener« Silanolgruppen (max. Extinktion bei etwa 3350–3450 cm^–1) sowie auch weitgehend unabhängig vom Wassergehalt (Feuchtigkeit) ist. Diese Tatsache wurde zur Ausarbeitung eines Routineverfahrens benutzt.

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Infrared-spectrophotometric determination of free silanol groups in pyrogenic silicic acids

Summary The technical properties of pyrogenic silicic acids are decisively co-determined by their content of so-called feee silanol groups. Their infrared absorption in a CCl₄ suspension belongs to a band at about 3,700cm^–1. It has been found that under certain conditions their maximum absorbance in CCl₄ is independent of the number of so-called bonded silanol groups (maximum absorption at about 3,350–3,450cm^–1), additionally existing in all commercial pyrogenic silicic acids, and also in wide ranges of the water content (humidity). This fact has been used as a basis for a quantitative routine determination of free silanol groups.

Zum Gedenken an Heinz Dannenberg     

Re-entrant isotropic behaviour of a pure double-swallow-tailed compound

Abstract

Two new six-ring double-swallow-tailed mesogens were prepared. The phase behaviours of these compounds were studied by optical methods and by calorimetry. One of them shows the very unusual phase sequence crystalline-smectic C-cubic-isotropic-nematic-isotropic.     

Sn-containing liquid crystalline side group homopolymers with two glass transitions

Three homologous tin-containing homopolymers with a terminal CN-dipole in the side group have been synthesized and characterized by dynamical calorimetry, polarization microscopy, X-ray and dielectric methods. AFM was used to evaluate the texture at room temperature. Four different phase transitions were detected by DSC. The high temperature phases were identified by polarization microscopy as SmA and SmC. AFM-measurements show focal-conic domains at room temperature and confirm so the smectic nature of all phases. X-ray measurements on nonoriented samples give hints to a phase segregation on nanometer scale. Dielectric investigation and temperature-modulated DSC (TMDSC) confirm clearly phase separation by appearance of two glass transitions related to the liquid order of the main chains and the liquid crystalline of the side groups.