Abdullatif Alfutimie

Underlying mechanism of the hydrothermal instability of Cu3(BTC)2 metal-organic framework

Water induced decomposition of Cu3(BTC)2 (BTC = benzene-1,3,5-tricarboxylate) metal-organic framework (MOF) was studied using dynamic water vapour adsorption. Small-angle X-ray scattering, Fourier transform infrared spectroscopy and differential scanning calorimetry analyses revealed that the underlying mechanism of Cu3(BTC)2 MOF decomposition under humid streams is the interpenetration of water molecules into Cu-BTC coordination to displace organic linkers (BTC) from Cu centres.

Chromonic liquid crystals formed by CI Acid Red 266 and related structures

Chromonic liquid crystals are currently receiving increased attention because they have applications in a wide range of products. In this study, we have compared the chromonic mesophase behaviour of four azo dyes with similar chemical structures. Our objective is to determine if there is an obvious link between mesophase formation and dye chemical structure. Orange G does not form mesophases over the concentration range examined (saturated solution > ~20–30 wt%). The other three compounds all form nematic (N) and hexagonal (H) mesophases, but over very different concentration ranges. X-ray diffraction shows that the ordered Edicol Sunset Yellow (ESY) aggregates present in the mesophases have a single molecule cross section, while those of CI Acid Red have a cross section equivalent to six to eight molecules, probably organised in a ‘water-filled pipes’ structure. NMR quadrupole splittings of 2H2O demonstrate that water binding to the aggregates is similar to that found for surfactant lyotropic mesophases. The sodium (23Na) quadrupole splittings for Orange II and CI Acid Red are similar to the values found for surfactant hexagonal phases, suggesting that most sodium ions are ‘bound’ to the aggregates. This is unlike the behaviour of ESY where only one of the two sodium ions is bound.

The influence of polar additives on chromonic mesophase formation of Edicol Sunset Yellow

Partial phase diagrams have been determined for the chromonic mesogen Edicol Sunset Yellow (ESY) in the presence of urea and formamide. Both additives reduce the composition ranges of the nematic and hexagonal phases compared to water alone, but the effects are quite small. Up to 10 m urea reduces the mesophase regions by ca 40°C. NMR measurements of 2H quadrupole splitting show that the interaction of urea with the ESY aggregates cannot be explained by the same simple ‘bound/free’ two-state model that fits the water binding. The addition of urea does not displace bound water, for example by competition with water for H-bonding sites. For the urea, there appears to be a larger fraction associated with the stacks on increasing ESY concentration. We suggest that this is due to urea molecules being ‘forced’ to occupy sites between the ESY within the stacks because of the restricted solvent regions (ca 1 nm), resulting in mesophase destabilisation.

The influence of sodium chloride and urea on chromonic liquid crystals formed by CI Acid Red 266

Chromonic liquid crystals are currently receiving renewed interest with particular attention on the Edicol Sunset Yellow (ESY)/water system, which forms columnar nematic and hexagonal phases. CI Acid red 266 is structurally fairly similar to ESY and also forms columnar nematic and hexagonal phases but at much lower concentrations (>1%). In this study, we have examined the influence of sodium chloride and urea on chromonic liquid crystals formed by CI acid red 266. The techniques employed were polarising microscopy, X-ray diffraction and 2H NMR. Sodium chloride moves the concentration at which mesophases form to higher values. Once formed, the mesophases are stable to slightly higher temperatures. Screening of the interstack electrostatic repulsions by added electrolyte appears to be responsible for the changes. Urea can be added in fairly large concentrations (up to 25 wt%) without significant changes in mesophase stability. X-ray diffraction measurements show that there is little change in the aggregate structure with added urea. NMR measurements on urea and water ordering show that urea has much larger order parameters than water. Both order parameters are much smaller than values reported for ESY, but this is simply because of the lower dye concentrations. The larger order parameters for urea appear to arise from some intercalation of urea into the acid red 266 stacks. There is no evidence for changes in ‘water structure’ by the addition of urea.

Effect of 2.94 μm Er: YAG laser on the chemical composition of hard tissues

The aim was to investigate the effect of the Er‐YAG laser radiation on morphology and chemical composition of enamel, dentin, and bone. The specimens of the three groups were irradiated with a very long pulse mode (VLP) of 2.94 µm Er‐YAG laser with 100 mJ pulse energy and energy density of 8.42 J/ cm2 for 30 s, at a repetition rate of 15 Hz. The organic and inorganic content of the samples were investigated by Fourier Transforms Infrared spectroscopy (FTIR). The morphological characteristics were investigated with scanning electron microscopy (SEM) and elemental analysis (calcium and phosphorus) with energy‐dispersive X‐ray spectroscopy (EDX). FTIR data were analyzed with a One‐Way ANCOVA test and EDX data with the independent sample t‐test. Following the laser radiation, FTIR showed a significant decrease in the organic content of all tissues. The weight percentage (wt %) calcium content of dentin and bone increased significantly following irradiation with a p‐value of .002 for both tissues, but the wt % of phosphorus content was not influenced significantly. The morphological alterations expressed signs of fusion in all the samples.