Structural study of a smectic C phase of biforked molecules

In the framework of a systematic investigation of the molecular organization in different mesophases exhibited by biforked molecules, we present a structural study of the smectic C phase of a biforked compound containing heptyloxy chains. With a combination of dilatometry measurements and X-ray diffraction on polydomain samples, together with a detailed X-ray investigation on oriented samples, it was possible to describe precisely the packing of the molecules within the smectic C layers. The result is a large tilt of the long aromatic cores of about 50°-60° with respect to the normal to the layer planes, whereas the terminal aliphatic chains are close to the normal to the planes with a small tilt angle of about 20°-30°. For the first time, these two angles have been directly observed on the X-ray patterns of oriented samples.     

Transitions between the B2 phase and more usual smectic phases in binary systems of banana-shaped with calamitic mesogens

Three phase diagrams of binary systems are presented where one of the mixing components is a bent-core mesogen and the other is a calamitic mesogen. In two of these systems transitions between the 'banana phase' B₂ and more usual smectic phases in the sequences B₂-SmA, B₂-SmC, B₂-SmC-SmA, B₂-SmC-SmA-N could be observed. The mesophases have been identified by their textures, by X-ray investigations and by electro-optical measurements.     

Combination of chemical and electron-impact ionisation with GC×GC–qMS for characterization of fatty alcohol alkoxylate polymers in the low-molecular-weight range up to 700 Da

The class of fatty alcohol alkoxylates describes surfactants that are synthesised by reaction of fatty alcohols with alkoxides such as ethylene oxide or propylene oxide or a combination of both as copolymers. Such alkoxylates are used, for example, as nonionic surfactants in home and industrial cleaning and washing agents. Chemical characteristics of such alkoxylate copolymers, for example the degree of alkoxylation, the arrangement of building blocks (random or block polymerisation), the type of the starter, and endcapping, play an important role in application behaviour. The analysis of these characteristics is challenging because in many cases such copolymers have high polydispersity and a large number of constitutional isomers depending on the degree of alkoxylation. Furthermore, the alkoxylates often occur in a complex multicomponent matrix. Here we present a method for characterization of silylated fatty alcohol alkoxylates in the low-molecular-weight range by means of comprehensive two-dimensional gas chromatography–mass spectrometry with electron impact and chemical ionisation. This method also enables detailed analysis of the alkoxylates in a complex matrix such as modern detergents.     

Intermolecular organization of triphenylene-based discotic mesogens by interdigitation of alkyl chains

Two homologous series of 2,3,6,7,10,11-hexa-alkyloxy-substituted triphenylenes have been synthesized, such that alkyl chains of two different lengths alternate around the rigid triphenylene core in order to allow interdigitation of the chains between neighbouring columns in a hexagonal columnar mesophase. We report here the dependence of structural and thermal properties on the extent of interdigitation, as investigated by X-ray diffraction, polarized optical microscopy and differential scanning calorimetry.     

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.     

Liquid crystalline swallow-tailed compounds (II) dielectric relaxation

Dielectric investigations in the kHz-range on swallow-tailed liquid crystals show a strong decrease of the dielectric constant as well as of the dielectric loss parallel to the nematic director with decreasing temperature. In the perpendicular direction no strong anomaly has been observed. By consideration of X-ray data of the S_A phase the dielectric results can be interpreted by the dipole-dipole interaction which is forced by the anisotropy of repulsive forces of the respective molecules.     

Highly Branched Alkanoic Acids from the Preen‐Gland Wax of the Domestic Goose as Building Blocks for Chiral Triphenylenes

The synthesis of chiral triphenylenes 7a , b bearing side chains derived from enantiomerically pure trimethyloctanoate 1a and tetramethyldecanoate 1b from the preen‐gland wax of domestic goose was achieved in 3 or 4 steps. Compounds 7a , b were nonmesogenic; however, mixtures of 7a , b with hexakis(octyloxy)triphenylene or hexakis(decyloxy)triphenylene displayed columnar mesophases or soft crystal G phases, as was shown by differential‐scanning calorimetry and optical‐polarizing microscopy. Circular‐dichroism measurements revealed weak associations of 7a , b in solution.     

The Structure and Unusual Optical Textures of Smectic C2 Phases of New Tail-to-Tail Twins

New tail-to-tail twins with alkyl or perfluorinated spacers were synthesized. The mesomorphic properties were studied by polarizing microscopy and X-ray diffraction measurements. It was found that the smectic C phase is a Sc₂ phase with alternating tilt and an intercalated structure. The alternating tilt gives rise to an unusual schlieren texture which exhibits not only singularities with the strength s = ±1 but also those with s = ±1/2 and s = ±3/2.     

Structure and Packing in Smectic E and Smectic A Phases in the Series of 4-n-Alkyloxy-4′-alkanoylbiphenyls

By means of X-ray investigations the structure of the S_E and S_A-phases of the title compounds has been studied. The lattice parameters of the orthorhombic S_E structure are given. The thickness of the smectic layers is nearly the same in the S_E and S_A phases and agrees well with the length of the molecules in their most stretched form. That suggests a similar conformation of the alkyl chains in both phases. A model of the packing in the S_A phase is discussed which is based on a dense packing with antiparallel orientation of molecules with a non-symmetrical shape.     

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.