Synthesis and smectogenic properties of novel phloroglucinol-based star-shaped liquid crystals containing three peripheral alkyloxylated Schiff base arms

A series of symmetrical trimeric liquid crystalline compounds of which the molecular structure with a central core of 1,3,5-benzene attached by three rod-like mesogenic Schiff base moieties via the propylene spacers and ether linkages has successfully been synthesised and characterised by infra red and nuclear magnetic resonance spectroscopic techniques. All the star-shaped compounds in this series exhibit predominantly SmC phase except the analogue possessing terminal C₈H₁₇ group. It is apparent that the members with even parity from C₁₀H₂₁ to C₁₆H₃₃ show enantiotropic SmC phase while the member with longest terminal chain of C₁₈H₃₇ is inclined to monotropic smectogen. The X-ray diffraction measurements reveal that the tilted smectic layer structures of the SmC phase are confirmed to have an obvious sharp peak at small angles of 2θ ～ 1.03°–1.48° with d-spacing values of 4.01–4.58 nm, which are corresponding to tilt angles of ～48° in the SmC phase.     

Heterocyclic benzothiazole-based liquid crystals: synthesis and mesomorphic properties

Two homologous series of 2-(4-alkanoyloxybenzylidenamino)benzothiazoles and 2-(2-hydroxy-4-alkanoyloxybenzylidenamino)benzothiazoles were synthesised and characterised. Their molecular structures differed wherein the latter comprised a lateral hydroxyl group, unlike the former. Spectroscopic techniques such as FT-IR, ¹H & ¹³C NMR and mass spectrometry together with elemental analysis were employed to elucidate the molecular structures. The transition temperatures and their mesophases were determined by differential scanning calorimetry, optical polarising microscopy and X-ray diffraction techniques. Members with decanoyloxy till hexadecanoloxy chain in the series without the lateral hydroxyl group each exhibited a smectic A phase, while those in the series with the lateral hydroxyl group were non-mesogenic. The mesomorphic properties of the present series were compared with other structurally related series to establish the chemical structure–mesomorphic properties relationship.     

Liquid crystal oligomers: going beyond dimers

This review focuses on structure-property relationships in liquid crystal oligomers, which consist of molecules containing two or more mesogenic units linked via flexible spacers essentially in a linear fashion and so does not consider, for example, liquid crystal dendrimers and tetrapodes. Previous reviews have tended to focus mainly on liquid crystal dimers in which just two mesogenic units are interconnected by a single spacer. By contrast, this review is largely devoted to higher oligomers such as liquid crystal trimers and tetramers containing three or four mesogenic units connected by two or three spacers, respectively.     

Non-symmetric chiral isoflavone dimers: synthesis,characterisation and mesomorphic behaviour

A new series of non-symmetric chiral isoflavone-based liquid crystalline dimers, α-(2-methylbutyl-4′-(4″-phenyloxy)benzoate)-ω-(3-(4′-decyloxyphenyl)-4H-1-benzopyran-4-one-7-oxy)alkanes, with 3–12 carbon atoms in the alkyloxy spacer, have been synthesised. A pronounced odd–even effect for the phase transition temperatures upon varying the spacer length was observed. The short dimers exhibited monolayer smectic A (SmA) and smectic C (SmC*) phases while for longer homologues a chiral nematic (N*) phase was found. The temperature range of the nematic phase was broadened with elongation of the alkyl spacer. Stabilisation of the nematic phase resulted from competition between the monolayer and intercalated smectic structures. The SmA–SmC* phase transition was second order for all studied compounds with a cross over to the de Vries type behaviour for the shortest homologue.     

Synthesis of new schiff base ester liquid crystals with a benzothiazole core

A series of new calamitic liquid crystals, 6-methoxy-2-(4-alkanoyloxybenzylidenamino)benzothiazoles, comprising a benzothiazole core, terminal methoxy group and a Schiff base linkage were synthesised and characterised. This series comprises 12 members wherein members differ by the length of the alkanoyloxy chain (C _n-1H_2n-1COO-, where n?=?2–8, 10, 12, 14, 16, 18). Their mesomorphic properties were studied by using differential scanning calorimetry, optical polarising microscopy and powder X-ray diffraction techniques. The short chain derivatives (n?=?2 and 3) were non-mesogenic compounds, while an enantiotropic nematic phase was present throughout the remaining members of the series. The smectic C phase emerged from the decanoyloxy derivative onwards.     

Characterization of the B4 phase by dielectric and AFM measurements

Dielectric measurements on a sample consisting of banana-shaped molecules were carried out in a frequency range between 0.1 Hz and 10 MHz. The sample exhibited B₂ and B₄ phases. As usual, two ranges of relaxation were detected in the B₂ phase, the fast reorientation about the long axes of the molecules and a slow collective process. In the B₄ phase, only one dielectric active process at low frequencies was found; this does not differ from the low frequency relaxation of the B₂ modification. This relaxation is probably related to the dynamics of superstructures. Crystallization could be observed after keeping the sample for a longer time at higher temperature. Thus, it was possible to differentiate clearly between the crystalline and the B₄ phases. AFM investigations prove the existence of focal-conic domains and periodic superstructures in the B₄ phase; then do not appear in the crystalline state. For this reason the B₄ phase is regarded as different from a classical crystalline phase.     

Synthesis of two-dimensional gallium nitride via spin coating method: influences of nitridation temperatures

This paper reports the synthesis and characterization of gallium nitride (GaN) thin films deposited on p-type silicon (100) substrates by using low cost spin coating method under various nitridation temperatures. This work demonstrated that spin coating with the new prepared precursor solution can be used as a versatile method for the successfully growth of GaN thin films. Furthermore, the influence of varying nitridation temperatures on the structural, morphological, and optical properties of synthesized GaN thin films were studied in this work. The GaN thin films were characterized by X-ray diffraction, field-emission scanning electron microscopy, atomic force microscopy, photoluminescence and Raman spectroscopy. All the characteristics of the GaN thin films were effectively improved with the increasing of the nitridation temperatures from 750 to 950 °C and degraded at temperature of 1,050 °C. The measured results show that nitridation temperature plays an important role in improving the crystalline quality of the GaN thin films and the most efficient nitridation temperature was at 950 °C.     

Mixed matrix vanadium oxide catalytic nanocomposite membrane for styrene oxidation

Mesoporous nanocomposite membranes with vanadium oxide–carbon nanotubes (V_xO_y-CNTs) embedded in γ-Al₂O₃ were successfully synthesized using the dip coating method. The membranes were evaluated for styrene oxidation to determine the optimum styrene conversion and benzaldehyde selectivity. Several factors that influence the preparation of defect-free coatings, such as the type of binder, the binder addition time and surface support treatments, were investigated. The physico-chemical permeation properties of the membranes were characterized using scanning electron microscope, transmission electron microscope (TEM), X-ray Diffraction XRD, Nitrogen adsorption (BET) and Thermogravimetric TGA. Response surface methodology (RSM) was used to investigate the effects of oxidant (H₂O₂) concentration, temperature, contact time and catalyst loading on styrene conversion and the selectivity of benzaldehyde. Based on the RSM analysis, the optimal oxidation conditions included a reaction temperature of 45 °C, a differential pressure of 1.5 bars, a molar ratio of H₂O₂: styrene of 1.5:1 and a catalyst loading of 30 %. These conditions resulted in the maximal styrene conversion of 25.6 and 84.9 % benzaldehyde selectivity.     

A one-pot tandem synthesis of various 1,2-disubstituted benzimidazoles

A facile method to synthesize various 1,2-disubstituted benzimidazoles is developed. It is suggested that formation of a Meisenheimer adduct between the substrate, amine, and solvent aids the N-arylation process. The generality of the protocol is demonstrated by the efficient reactions involving numerous substituents ranging from electron-withdrawing groups to electron-donating groups.     

Uranium concentration in blood samples of Southern Iraqi leukemia patients using CR-39 track detector

The simple and effective technique of fission track etch has been applied to determine trace concentration of uranium in human blood samples taken from two groups of male and female participants: leukemia patients and healthy subjects group. The blood samples of leukemia patients and healthy subjects were collected from three key southern governorates namely, Basrah, Muthanna and Dhi-Qar. These governorates were the centers of intensive military activities during the 1991 and 2003 Gulf wars, and the discarded weapons are still lying around in these regions. CR-39 track detector was used for registration of induced fission tracks. The results show that the highest recorded uranium concentration in the blood samples of leukemia patients was 4.71 ppb (female, 45 years old, from Basrah) and the minimum concentration was 1.91 ppb (male, 3 years old, from Muthanna). For healthy group, the maximum uranium concentration was 2.15 ppb (female, 55 years old, from Basrah) and the minimum concentration was 0.86 ppb (male, 5 years old, from Dhi-Qar). It has been found that the uranium concentrations in human blood samples of leukemia patients are higher than those of the healthy group. These uranium concentrations in the leukemia patients group were significantly different (P < 0.001) from those in the healthy group.