[Fe(μ-btzmp)2(btzmp)2](ClO4)2:a doubly-bridged 1D spin-transition bistetrazole-based polymer showing thermal hysteresis behaviour

The reaction of btzmp (1,2-bis(tetrazol-1-yl)-2-methylpropane) with Fe(ClO4)2 generates a 1D polymeric species, [Fe(μ-btzmp)2(btzmp)2](ClO4)2, showing a steep spin transition (T½↑ = 136 K and T ½↓ = 133 K) with a 3 K thermal hysteresis. The crystal structure at 100 and 200 K reveals that, in contrast to other bistetrazole based spin-transition systems such as [Fe(endi)3](BF4)2 and [Fe(btzp)3](ClO4)2, the present compound has only two ligands bridging the metallic centres, while the other two coordination positions are occupied by two mono-coordinated (non-bridging) btzmp ligands. This peculiarity confers an unprecedented crystal packing in the series of 1D bistetrazole based polymers. The change in spin state is accompanied by an order/disorder transition of the ClO4- counterion. A careful examination of the structural changes occurring upon the spin transition indicates that this order/disorder is most likely affected by the modification of the [tetrazole-centroid]-ND-Fe angle (which is typical of bistetrazole spin-transition materials). Apart from X-ray analysis, also magnetic susceptibility, Mössbauer and UV-vis spectroscopies have been used to characterise the HS and the LS states of [Fe(µ-btzmp)2(btzmp)2](ClO4)2. © The Royal Society of Chemistry.

Investigating the structure of biomass-derived non-graphitizing mesoporous carbons by electron energy loss spectroscopy in the transmission electron microscope and X-ray photoelectron spectroscopy

We have investigated the microstructure and bonding of two biomass-based porous carbon chromatographic stationary phase materials (alginic acid-derived Starbon® and calcium alginate-derived mesoporous carbon spheres (AMCS) and a commercial porous graphitic carbon (PGC), using high resolution transmission electron microscopy, electron energy loss spectroscopy (EELS), N2 porosimetry and X-ray photoelectron spectroscopy (XPS). The planar carbon sp -content of all three material types is similar to that of traditional nongraphitizing carbon although, both biomass-based carbon types contain a greater percentage of fullerene character (i.e. curved graphene sheets) than a non-graphitizing carbon pyrolyzed at the same temperature. This is thought to arise during the pyrolytic breakdown of hexauronic acid residues into C5 intermediates. Energy dispersive X-ray and XPS analysis reveals a homogeneous distribution of calcium in the AMCS and a calcium catalysis mechanism is discussed. That both Starbon® and AMCS, with high-fullerene character, show chromatographic properties similar to those of a commercial PGC material with extended graphitic stacks, suggests that, for separations at the molecular level, curved fullerene- like and planar graphitic sheets are equivalent in PGC chromatography. In addition, variation in the number of graphitic layers suggests that stack depth has minimal effect on the retention mechanism in PGC chromatography. © 2013 Elsevier Ltd. All rights reserved.

Analysis of functional materials by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) can play an important role in guiding the design of new materials, tailored to meet increasingly stringent constraints on performance devices, by providing insight into their surface compositions and the fundamental interactions between the surfaces and the environment. This chapter outlines the principles and application of XPS as a versatile, chemically specific analytical tool in determining the electronic structures and (usually surface) compositions of constituent elements within diverse functional materials. Advances in detector electronics have opened the way for development of photoelectron microscopes and instruments with XPS imaging capabilities. Advances in surface science instrumentation to enable time-resolved spectroscopic measurements offer exciting opportunities to quantitatively investigate the composition, structure and dynamics of working catalyst surfaces. Attempts to study the effects of material processing in realistic environments currently involves the use of high- or ambient-pressure XPS in which samples can be exposed to reactive environments.

Scavenging of halogen in recycling of halogen-based polymer materials

Pyrolytic recycling of materials for electronics and automotive is attractive because of the possibility of recovery of fuel and of precious metals from printed circuit. Due to the complexity of their composition an appropriate pre-treatment has to be performed in order to limit the evolution of dangerous halogen containing compounds which strongly impair the fuel quality. An advantageous pyrolysis approach implies the attempt of mineralisation of the organic bromine to the not volatile and harmless inorganic form using strong bases such as NaOH and KOH to reduce the amount of volatile and increasing the residue. The char stability is greatly variable depending on the substrate. Mg(OH)2 and Ca(OH)2 behave in a similar manner but to a lower extent. Carbonates and reducing agent such as LiAlH have been tested as well and their ability to scavenge bromine is discussed in terms of effectiveness and mechanism.

Simultaneous strain and temperature measurement of advanced 3-D braided composite materials using an improved EFPI/FBG system

Simultaneous strain and temperature measurement for advanced 3-D braided composite materials using fibre-optic sensor technology is demonstrated, for the first time. These advanced 3-D braided composites can virtually eliminate the most serious problem of delamination for conventional composites. A tandem in-fibre Bragg-grating (FBG)/extrinsic Fabry-Perot interferometric sensor (EFPI) system with improved accuracy has been used to facilitate simultaneous temperature and strain measurement in this work. The non-symmetric distortion of the optical spectrum of the FBG, due to the combination of the FBG and the EFPI, is observed for the first time. Experimental and theoretical studies indicate that this type of distortion can affect the measurement accuracy seriously and it is mainly caused by the modulation of the periodic output of the EFPI. A simple method has been demonstrated to improve the accuracy for detection of the wavelength-shift of the FBG induced by temperature change. A strain accuracy of ∼ ±20 με and a temperature accuracy of ∼ ±1 °C have been achieved, which can meet the requirements for practical applications of 3-D braided composites. © 2002 Elsevier Science Ltd. All rights reserved.

Bioactive organic/inorganic hybrids with improved mechanical performance

New sol-gel functionalized poly-ethylene glycol (PEGM)/SiO2-CaO hybrids were prepared with interpenetrating networks of silica and PEGM through the formation of Si-O-Si bonds. Bioactive and mechanical properties were investigated for a series of hybrids containing varying organic/inorganic ratios and PEG molecular weights. In contrast to the unmodified PEG/SiO2-CaO hybrids, which rapidly dissolved and crumbled, the epoxy modified hybrids exhibited good mechanical properties and bioactivity. The compressive strength and Young's modulus were greater for higher molecular weight PEGM hybrids (PEGM600 compared to PEGM300). Compressive strengths of 138 MPa and 81 MPa were found for the 50: 50 and 60: 40 organic/inorganic hybrid samples respectively, which are comparable with cortical bone. Young's modulus values of ∼800 MPa were obtained for the 50 : 50 and 60 : 40 organic/inorganic hybrids. Bioactivity tests were conducted by immersing the hybrids into simulated body fluid and observing the formation of apatite. Apatite formation was observed within 24 hours of immersion. PEGM600 hybrids showed enhanced apatite formation compared to PEGM300 hybrids. Increased apatite formation was observed with increasing organic/inorganic ratio. 70 : 30 and 60 : 40 hybrids exhibited the greatest apatite formation. All PEGM hybrids samples had good cell viability and proliferation. The 60 : 40 PEGM600 hybrids displayed the optimal combination of bioactivity and mechanical strength. The bioactivity of these hybrids, combined with the enhanced mechanical properties, demonstrate that these materials have significant potential for bone regeneration applications.

Design of experiments to study the impact of process parameters on droplet size and development of non-invasive imaging techniques in tablet coating

Atomisation of an aqueous solution for tablet film coating is a complex process with multiple factors determining droplet formation and properties. The importance of droplet size for an efficient process and a high quality final product has been noted in the literature, with smaller droplets reported to produce smoother, more homogenous coatings whilst simultaneously avoiding the risk of damage through over-wetting of the tablet core. In this work the effect of droplet size on tablet film coat characteristics was investigated using X-ray microcomputed tomography (XμCT) and confocal laser scanning microscopy (CLSM). A quality by design approach utilising design of experiments (DOE) was used to optimise the conditions necessary for production of droplets at a small (20 μm) and large (70 μm) droplet size. Droplet size distribution was measured using real-time laser diffraction and the volume median diameter taken as a response. DOE yielded information on the relationship three critical process parameters: pump rate, atomisation pressure and coating-polymer concentration, had upon droplet size. The model generated was robust, scoring highly for model fit (R2 = 0.977), predictability (Q2 = 0.837), validity and reproducibility. Modelling confirmed that all parameters had either a linear or quadratic effect on droplet size and revealed an interaction between pump rate and atomisation pressure. Fluidised bed coating of tablet cores was performed with either small or large droplets followed by CLSM and XμCT imaging. Addition of commonly used contrast materials to the coating solution improved visualisation of the coating by XμCT, showing the coat as a discrete section of the overall tablet. Imaging provided qualitative and quantitative evidence revealing that smaller droplets formed thinner, more uniform and less porous film coats.