Derivation of an urban materials spectral library through emittance and reflectance spectroscopy

Recent advances in thermal infrared remote sensing include the increased availability of airborne hyperspectral imagers (such as the Hyperspectral Thermal Emission Spectrometer, HyTES, or the Telops HyperCam and the Specim aisaOWL), and it is planned that an increased number spectral bands in the long-wave infrared (LWIR) region will soon be measured from space at reasonably high spatial resolution (by imagers such as HyspIRI). Detailed LWIR emissivity spectra are required to best interpret the observations from such systems. This includes the highly heterogeneous urban environment, whose construction materials are not yet particularly well represented in spectral libraries. Here, we present a new online spectral library of urban construction materials including LWIR emissivity spectra of 74 samples of impervious surfaces derived using measurements made by a portable Fourier Transform InfraRed (FTIR) spectrometer. FTIR emissivity measurements need to be carefully made, else they are prone to a series of errors relating to instrumental setup and radiometric calibration, which here relies on external blackbody sources. The performance of the laboratory-based emissivity measurement approach applied here, that in future can also be deployed in the field (e.g. to examine urban materials in situ), is evaluated herein. Our spectral library also contains matching short-wave (VIS–SWIR) reflectance spectra observed for each urban sample. This allows us to examine which characteristic (LWIR and) spectral signatures may in future best allow for the identification and discrimination of the various urban construction materials, that often overlap with respect to their chemical/mineralogical constituents. Hyperspectral or even strongly multi-spectral LWIR information appears especially useful, given that many urban materials are composed of minerals exhibiting notable reststrahlen/absorption effects in this spectral region. The final spectra and interpretations are included in the London Urban Micromet data Archive (LUMA; http://LondonClimate.info/LUMA/SLUM.html).

Ordered-defect sulfides as thermoelectric materials

The thermoelectric behaviour of the transition-metal disulphides n-type NiCr2S4 and p-type CuCrS2 is investigated. Materials prepared by high-temperature reaction were consolidated using cold-pressing and sintering, hot-pressing (HP) in graphite dies or spark-plasma sintering (SPS) in tungsten carbide dies. The consolidation conditions have a marked influence on the electrical transport properties. In addition to the effect on sample density, altering the consolidation conditions results in changes to the sample composition, including the formation of impurity phases. Maximum room-temperature power factors are 0.18 mW m-1 K-2 and 0.09 mW m-1 K-2 for NiCr2S4 and CuCrS2, respectively. Thermal conductivities of ca. 1.4 and 1.2 W m-1 K-1 lead to figures of merit of 0.024 and 0.023 for NiCr2S4 and CuCrS2, respectively.

Supramolecular materials for inkjet printing: self-assembling polymer networks

Electronically complementary, low molecular weight polymers that self-assemble through tuneable π-π stacking interactions to form extended supramolecular polymer networks have been developed for inkjet printing applications and successfully deposited using three different printing techniques. Sequential overprinting of the complementary components results in supramolecular network formation through complexation of π-electron rich pyrenyl or perylenyl chain-ends in one component with π-electron deficient naphthalene diimide residues in a chain-folding polyimide. The complementary π-π stacked polymer blends generate strongly coloured materials as a result of charge-transfer absorptions in the visible spectrum, potentially negating the need for pigments or dyes in the ink formulation. Indeed, the final colour of the deposited material can be tailored by changing varying the end-groups of the π electron rich polymer component. Piezoelectric printing techniques were employed in a proof of concept study to allow characterisation of the materials deposited, and a thermal inkjet printer adapted with imaging software enabled a detailed analysis of the ink-drops as they formed, and of their physical properties. Finally, continuous inkjet printing allowed greater volumes of material to be deposited, on a variety of different substrate surfaces, and demonstrated the utility and versatility of this novel type of ink for industrial applications.

Recent developments in nanostructured materials for high-performance thermoelectrics

This highlight discusses recent trends in the search for new high-efficiency thermoelectric materials. Thermoelectric materials offer considerable attractions in the pursuit of a more efficient use of existing energy resources, as they may be used to construct power-generation devices that allow useful electrical power to be extracted from otherwise waste heat. Here, we focus on the significant enhancements in thermoelectric performance that have been achieved through nanostructuring. The principal factor behind the improved performance appears to be increased phonon scattering at interfaces. This results in a substantial reduction in the lattice contribution to thermal conductivity, a low value of which is a key requirement for improved thermoelectric performance.

Hybrid materials through linkage of chalcogenide tetrahedral clusters

Tetrahedral chalcogenide clusters, with their well-defined molecular structures and interesting properties, are attractive building blocks for hybrid materials, in which porosity may be integrated with electronic or optical properties. Linkage of tetrahedral clusters often occurs through bridging chalcogenolate ligands, and results in extended structures of inorganic connectivity. However, linkage of tetrahedral clusters via organic ligands is also possible and a number of coordination polymers have already been reported. Recent advances on the synthesis and crystal structures of extended hybrid structures based on tetrahedral clusters are described here.

Thermoelectric materials: a new rapid synthesis process for non-toxic and high-performance tetrahedrite compounds

The feasibility to synthesize, in large quantity, pure and non-toxic tetrahedrite compounds using high-energy mechanical-alloying from only elemental precursors is reported in the present paper for the first time. Our processing technique allows a better control of the final product composition and leads to high thermoelectric performances (ZT of 0.75 at 700 K), comparable to that reported on sealed tube synthesis samples. Combined with spark plasma sintering, the production of highly pure and dense samples is achieved in a very short time, at least 8 times shorter than in conventional liquid-solid-vapor synthesis process. The process described in this paper is a promising way to produce high performance tetrahedrite materials for cost-effective and large-scale thermoelectric applications.

Novel glycopolymer hydrogels as mucosa-mimetic materials to reduce animal testing

Glycopolymer hydrogels capable of mimicking mucosal tissue in mucoadhesion testing have been designed. Liquid formulations containing mucoadhesive polymers were found to be retained on these tissues to the same extent as ex vivo gastric mucosa, when using a dynamic method of assessing mucoadhesion.

Supramolecular materials: longer and safer gastric residence

A supramolecular polymer that is stable in the acidic environment of the stomach but dissolves in the neutral-pH environment of the intestines prolongs the safe retention of gastric devices.

Organically-functionalised supertetrahedra as building blocks for hybrid materials

The crystal structures of gallium sulfides prepared under solvothermal conditions, using 4-picoline as a solvent, are described. These materials contain [Ga10S16(NC6H7)4]2− clusters, in which the terminal S2− anions have been replaced by covalently bonded 4-picoline molecules. Whilst these phases contain isolated supertetrahedral clusters separated by organic moieties, linkage of such clusters via organic ligands is possible under suitable reaction conditions. These organically-functionalised supertetrahedra could therefore be used to design novel Metal-Organic frameworks (MOFs) in which the normally-encountered metal centers are replaced by supertetrahedral clusters.