Interesting Class Of Materials Research Articles

A chemists view: Metal oxides with adaptive structures for thermoelectric applications

Thermoelectric devices can help to tackle future challenges in the energy sector through the conversion of waste heat directly into usable electric energy. For a wide applicability low‐cost materials with reasonable thermoelectric performances and cost‐efficient preparation techniques are required. In this context metal oxides are an interesting class of materials because of their inherent high‐temperature stability and relative high sustainability. Their thermoelectric performance, however, needs to be improved for wide application. Compounds with adaptive structures are a very interesting class of materials. A slight reduction of early transition metal oxides generates electrons as charge carriers and crystallographic shear planes as structure motif. The crystallographic shear planes lead to a reduction of intrinsic thermal conductivity. At the same time, the electronic transport properties can be tuned by the degree of reduction. So far only a few transition metal oxides with adaptive structures have been investigated with respect to their thermoelectric properties, leaving much room for improvement. This review gives an overview of thermoelectric oxides, highlights the structural aspects of the crystallographic shear planes and the resulting thermoelectric properties.

Aluminum foam made via a new method based on cold gas dynamic sprayed powders mixed through sound assisted fluidization technique

Metal foams are an interesting class of materials with very low specific weight and unusual physical, mechanical and acoustic properties due to the porous structure. In recent years several manufacturing techniques were developed. The limit of these techniques is that it is difficult, even if impossible, to manufacture precursors and then foams able to reinforce complex shaped components; this drawback, to date, limits the application of metal foams. This proof of concept paper is focused on the study of an innovative manufacturing technique able to produce complex shaped precursors. The key idea is to spray a powder mixture (made of both aluminum alloy powders as metal matrix and titanium hydride particles as foaming agent) through the cold gas dynamic spray on a free shape metallic substrate and then carry out the foaming process. A preliminary granulometric analysis was carried out to estimate the particles mean size and then sound assisted (140dB–80Hz) fluidization process was used to achieve a homogenous and deep mixing between the fine metal powders and the blowing agent ones. In particular, two different types of mixtures with 1wt% and 2.5wt% of TiH2 were investigated; moreover, air compressed as well as helium were used as CGDS carrier gas in order to ensure a higher impact velocity and a better compacting of the powders. Finally, the cross sections of manufactured solid foams were observed by means of a SEM microscope for having information about internal metallurgical phenomena as well as the distribution and morphology of foam cells. Macrographs of created porous structures showed the effectiveness of the developed innovative manufacturing process.

Responsive hydrogel nanoparticles for pulmonary delivery

Nanoparticles represent one of the most widely studied classes of advanced drug delivery platforms in recent years due to a wide range of unique properties and capabilities that can be utilized to improve upon traditional drug administration. Conversely, hydrogel nanoparticles (HNPs) – also called nanogels – represent a unique class of materials that combine the intrinsic advantages of nanotechnology with the inherent capabilities of hydrogels. Responsive hydrogels pose a particularly interesting class of materials that can sense and respond to external stimuli and previous reports of inhalable hydrogel particles have highlighted their potential in pulmonary delivery. Here, we synthesized two different pH-responsive HNPs, designated HNP120 and HNP270, by incorporating functional monomers with a common crosslinker and characterized their physicochemical properties. One of the HNP systems was selected for incorporation into a composite dry powder by spray drying, and the aerodynamic performance of the resulting powder was evaluated. The HNP120s displayed a hydrodynamic diameter of approximately 120 nm in their fully swollen state and a minimal diameter of around 80 nm while the HNP270s were approximately 270 nm and 115 nm, respectively. Electron microscopy confirmed particle size- and morphological uniformity of the HNPs. The HNP120s were spray dried into composite dry powders for inhalation and cascade impaction studies showed good aerosol performance with a mass median aerodynamic diameter (MMAD) of 4.82 ± 0.37 and a fine particle fraction > 30%. The HNPs released from the spray dried composites retained their responsive behavior thereby illustrating the potential for these materials as intelligent drug delivery systems that combine the advantages of nanotechnology, lung targeting through pulmonary delivery, and stimuli-responsive hydrogels.

ChemInform Abstract: Transport Properties of Hybrids with Ferromagnetic MnAs Nanoclusters and Their Potential for New Magnetoelectronic Devices

AbstractReview: 161 refs.

Molecular dynamics simulations of alkyl substituted nanographene crystals

Discotic polyaromatic molecules, similar to nanometric graphene flakes, constitute an interesting class of materials for organic electronic applications. Grafting flexible side chains around the periphery of such molecules enhances their processability and gives rise to diverse behaviours, such as the manifestation of liquid-crystalline character and anisotropic mechanical response. In this work, we examine by means of molecular dynamics simulations the properties of molecular crystals comprised of alkyl-substituted hexa-peri-hexabenzocoronene mesogens. Pristine and mono-substituted systems by hydrogen or iodine atoms are modelled, with variable side chain length. A general structural and mechanical robustness to peripheral substitution is reported, with the mesogens forming tightly packed molecular wires even at elevated temperature and pressure. In their discotic ordering, the molecules present relatively low translational mobility, a beneficial phenomenon for charge transport. A thermotropic dependence of the mechanical response is identified, with the systems behaving differently in their room-temperature crystalline phase and in their liquid-crystalline phase at elevated temperatures. The melting process is also examined, elucidating an initial negative expansion along a high symmetry direction and the existence of a metastable state, before falling into the final liquid-crystalline state.

Transport properties of hybrids with ferromagnetic MnAs nanoclusters and their potential for new magnetoelectronic devices.

Granular hybrid structures containing ferromagnetic nanoclusters embedded in a semiconducting matrix are an interesting class of materials as their properties can be tuned in a wide range. Hybrids are a promising alternative to dilute magnetic semiconductors in the field of spintronics and magnetoelectronics, because the nanoclusters can show ferromagnetic behavior even at room temperature. In this review, it is focused on the rather well investigated dilute magnetic semiconductor (Ga,Mn)As with MnAs inclusions. Different preparation methods are presented which were developed over the last two decades in order to obtain MnAs nanoclusters in the semiconducting matrix and to tune the structural and magnetic properties of these clusters. Recent results on the influence of the nanoclusters on the hybrids' transport properties as well as first approaches to use hybrids with a random nanocluster distribution in new spintronic devices are discussed. In addition, the perspective of using single MnAs nanoclusters as well as ordered arrangements of a few nanoclusters in new planar magnetoelectronic devices is illustrated.

Lithium transition metal pnictides – structural chemistry, electrochemistry, and function

AbstractLithium-transition metal (T)-pnictides (Pn=P, As, Sb, Bi) are an interesting class of materials with greatly differing crystal structures. The transition metal and pnictide atoms build up covalently bonded networks that leave cavities or channels for the lithium atoms. Depending on the bonding of lithium to the polyanionic network, one observes mobility of the lithium atoms. The crystal chemistry, chemical bonding,7Li solid-state NMR, and the electrochemical behavior of the pnictides are reviewed. The structural chemistry is compared with related tetrelides.

One dimensional BaxSr1 − xEryFe12 − yO19 fibers with magnetic crystalline nanoparticles

Hexagonal ferrites, also known as hexaferrites, are a very interesting class of materials with peculiar magnetic and electrical properties. Recently, several applications, both commercial and technological, have been developed by employing such materials, such as in magnetic recording and separation, storage devices, and catalysts. In particular, one dimensional magnetic nanostructured materials are very promising since they exhibit physical properties that cannot be found in the bulk. In this work, nanocrystalline Sr1 − xBaxEryFe12 − yO19 (x = y ⩽ 0.4) ferrite fibers are successfully fabricated by sol-gel spinning, followed by calcination. By varying the calcination temperature and content of substituted ions, different ferrite fibers have been obtained, which exhibit different magnetic properties and structural characteristics. Our capacity to effectively tune the magnetic properties of one dimensional hexagonal ferrite materials opens new scenarios towards the design and optimization of a multitude of devices that are based on the magnetic properties of hexaferrites.

Investigation of redox activity in the napthalenediimide-poly(3,4-ethylenedioxythiophene) cross-linked polymers

Electroactive polymers, based on the concept of linking a redox-active core to a backbone with high electronic conductivity, are a class of interesting materials because of the possibility to independently control different properties like electrochromic contrast, conductivity, charge capacity and redox potential window by the proper choice of the two distinct components employed. In this regard, we recently developed a new napthalenediimide-poly(3,4-ethylenedioxythiophene) crosslinked polymer, which was applied in electrochromic and energy storage devices. In this paper the electrochemical characterization of the polymer by cyclic voltammetries and electrochemical quartz crystal microbalance investigations is described. The redox process of the polymer backbone shows the characteristic features of p-doping conducting polymers while the napthalenediimide redox units have a bi-electronic molecular like electrochemistry that strongly depends on the electrolyte cation. The polymer mass change during the voltammetric cycles reveals the role of the solvent in balancing the mass flux across the layer.

Investigations on the Antiretroviral Activity of Carbon Nanotubes Using Computational Molecular Approach

Carbon nanotubes are the interesting class of materials with wide range of applications. They have excellent physical, chemical and electrical properties. Numerous reports were made on the antiviral activities of carbon nanotubes. However the mechanism of antiviral action is still in infancy. Herein we report, our recent novel findings on the molecular interactions of carbon nanotubes with the three key target proteins of HIV using computational chemistry approach. Armchair, chiral and zigzag CNTs were modeled and used as ligands for the interaction studies. The structure of the key proteins involved in HIV mediated infection namely HIV- Vpr, Nef and Gag proteins were collected from the PDB database. The docking studies were performed to quantify the interaction of the CNT with the three different disease targets. Results showed that the carbon nanotubes had high binding affinity to these proteins which confirms the antagonistic molecular interaction of carbon nanotubes to the disease targets. The modeled armchair carbon nanotubes had the binding affinities of -12.4 Kcal/mole, -20 Kcal/mole and -11.7 Kcal/mole with the Vpr, Nef and Gag proteins of HIV. Chiral CNTs also had the maximum affinity of -16.4 Kcal/mole to Nef. The binding affinity of chiral CNTs to Vpr and Gag was found to be -10.9 Kcal/mole and -10.3 Kcal/mole respectively. The zigzag CNTs had the binding affinity of -11.1 Kcal/mole with Vpr, -18.3 Kcal/mole with Nef and -10.9 with Gag respectively. The strong molecular interactions suggest the efficacy of CNTs for targeting the HIV mediated retroviral infections.

Novel synthesis and electropolymerization of metallo-conjugated thiophene derivatives

Metal-containing conducting polymers are a new and interesting class of materials that combine some of the redox properties of conducting polymers and some of those of the metal ions. In metal-containing conjugated polymers, there are several possible arrangements of metal group relative to the backbone. In this study, new conducting metallo-polymers were designed with the incorporation of valeric bimetallic carboxylic acid complex and 4-hydroxy benzoic acid based on η6-aryl-η5-cyclopentadienyliron and ferrocene-3-carboxylic acid to hydroxymethyl EDOT (thieno[3,4-b]-1,4-dioxin-2-methanol) and 2-(3-thienyl)ethanol. The resulting monomers were then polymerized electrochemically by having the conjugated system as a backbone and the metallic moiety pendant to the backbone. On the other hand, the monomers were chemically polymerized with Bisphenol-A to retain the metal moiety in the backbone of the polymer, affording the possibility of strong electronic interactions between the organic bridge and metal group in this arrangement. Spectroscopic, thermal, and electrochemical characterizations were performed to highlight the structural attributes of the polymers. Morphological characterization revealed that the electrochemically modified electrode surfaces have a very porous surface area.

Transition metal phthalocyanines: Insight into the electronic structure from soft x-ray spectroscopy

Transition metal phthalocyanines (MPc's) are an interesting class of material, and their magnetic and electronic properties are determined by the orbital occupation of the transition metal 3d orbitals incorporated in the molecules center. Thus, the ground state configuration of the transition metal center is very important for a complete understanding of these materials. We present experimental data taken using x-ray absorption and x-ray photoemission spectroscopy together with a theoretical interpretation of MPc series with M=Zn, Cu, Ni, Co, Fe, and Mn. The combination of these methods allows us to narrow down possible dominating ground state configurations and shed a brighter light on the electronic structure of these complexes.

Electrical conductivity of polyurethane/MWCNT nanocomposite foams

AbstractPolymeric foams with electrical conductivity represent a novel and very interesting class of materials rather sporadically studied. In this study, the feasibility to prepare electrically conductive Rigid Polyurethane (PUR) foams at various densities using multiwall carbon nanotubes (MWCNT) at varying contents was investigated. The produced PUR/MWCNT foams exhibited electrical conductivity over a wide range of densities and nanofiller contents. The effect of these two parameters on the electrical conductivity of the final foam system was studied. To explain the behavior, Statistical Percolation laws were employed. Model parameters were elaborated for both cases showing that the percolation model can adequately describe the behavior. The foaming process is analyzed in further detail to assist in the explanation and understanding of theexperimental observations. Finally, a material design map is proposed for the preparation of electrically conductive foams. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Self-assembling peptide hydrogels promote microglial cells proliferation and NGF production

Peptidic hydrogels are an interesting class of materials, with potential applications in tissue engineering and controlled drug delivery. Fmoc–Phe3 self-assembling peptide was synthesized in an aqueous phase by using a lipase from Pseudomonas fluorescens. The bioconversion afforded a self-supporting hydrogel in only 10 minutes, a feature that seems very promising for biotechnological applications. The rheological properties of such material were studied. The peptide hydrogel, used as a scaffold for culturing rat microglial cells, induced a significant cell proliferation and an increased production of the neurotrophic factor NGF. Moreover, microscopy studies demonstrated that the hydrogel was able to promote microglial cell adhesion.

Metal sulfide–polymer nanocomposite thin films prepared by a direct formation route for photovoltaic applications

Blends of conjugated polymers and inorganic semiconductors are an interesting class of materials with various applications in the field of plastic electronics. This work presents a direct approach to obtain composites consisting of a conjugated polymer, poly(3-(ethyl-4-butanoate)thiophene) (P3EBT), and a sulfur-based semiconductor (i.e. CdS, PbS or ZnS) using an in-situ formation route. The metal sulfide semiconductor is formed by reaction of the corresponding metal salt (cadmium acetate, zinc acetate or lead thiocyanate) dispersed within the conjugated polymer matrix with thiourea at temperatures below 200 °C. Nanoscaled networks are formed in the case of the CdS- and ZnS-P3EBT composites as shown by X-ray diffraction and transmission electron microscopy investigations, whereas the PbS-P3EBT blend exhibits inorganic structures on the μm-scale. The materials were used as active layer in bulk-heterojunction type hybrid solar cells. First photovoltaic devices containing an active layer of CdS- or ZnS-P3EBT show photovoltaic action, though efficiencies are low (≤ 0.06%).

Vitalising porous inorganic silica networks with organic functions—PMOs and related hybrid materials

Mesoporous organic-inorganic hybrid materials are an interesting class of materials, which combine the advantages of two worlds; the inorganic part builds a robust substrate while organic functions make them alive in a way that they can be potentially used in a number of applications. In this tutorial review, we provide an overview of how mesoporous materials are synthesised via the 'soft template' path and how the incorporation of organic functions can be achieved. Furthermore, a colourful survey full of examples is presented, providing a small overview of field of applications that can potentially benefit from the use of periodic mesoporous organosilicas (PMOs) and related materials.

Lithium-Transition Metal-Tetrelides – Structure and Lithium Mobility

Abstract Lithium-transition metal (T)-tetrelides (tetr.= C, Si, Ge, Sn, Pb) are an interesting class of materials with greatly differing crystal structures. The transition metal and tetrel atoms build up covalently bonded networks which leave cavities or channels for the lithium atoms. Depending on the bonding of the lithium atoms to the polyanionic network one observes mobility of the lithium atoms. The crystal chemistry, chemical bonding, 7Li solid state NMR, and the electrochemical behavior of the tetrelides are reviewed herein.

ChemInform Abstract: Rare‐Earth Activated Nitride Phosphors: Synthesis, Luminescence and Applications

AbstractReview: 51 refs.

Rare-Earth Activated Nitride Phosphors: Synthesis, Luminescence and Applications

Nitridosilicates are structurally built up on three-dimensional SiN4 tetrahedral networks, forming a very interesting class of materials with high thermomechanical properties, hardness, and wide band gap. Traditionally, nitridosilicates are often used as structural materials such as abrasive particles, cutting tools, turbine blade, etc. Recently, the luminescence of rare earth doped nitridosilicates has been extensively studied, and a novel family of luminescent materials has been developed. This paper reviews the synthesis, luminescence and applications of nitridosilicate phosphors, with emphasis on rare earth nitrides in the system of M-Si-Al-O-N (M = Li, Ca, Sr, Ba, La) and their applications in white LEDs. These phosphors exhibit interesting luminescent properties, such as red-shifted excitation and emission, small Stokes shift, small thermal quenching, and high conversion efficiency, enabling them to use as down-conversion luminescent materials in white LEDs with tunable color temperature and high color rendering index.

ChemInform Abstract: Electrides: Early Examples of Quantum Confinement

Electrides are ionic solids with cavity-trapped electrons, which serve as the anions. Localization of electrons in well-defined trapping sites and their mutual interactions provide early examples of quantum confinement, a subject of intense current interest. We synthesized the first crystalline electride, Cs(+)(18-crown-6)(2)e(-), in 1983 and determined its structure in 1986; seven others have been made since. This Account describes progress in the synthesis of both organic and inorganic electrides and points to their promise as new electronic materials. Combined studies of solvated electrons in alkali metal solutions and the complexation of alkali cations by crown ethers and cryptands made electride synthesis possible. After our synthesis of crystalline alkalides, in which alkali metal anions and encapsulated alkali cations are present, we managed to grow crystalline electrides from solutions that contained complexed alkali cations and solvated electrons. Electride research is complicated by thermal instability. Above approximately -30 degrees C, trapped electrons react with the ether groups of crown ethers and cryptands. Aza-cryptands replace ether oxygens with less reactive tertiary amine groups, and using those compounds, we recently synthesized the first room-temperature-stable organic electride. The magnetic and electronic properties of electrides depend on the geometry of the trapping sites and the size of the open channels that connect them. Two extremes are Cs(+)(15-crown-5)(2)e(-) with nearly isolated trapped electrons and K(+)(cryptand 2.2.2)e(-), in which spin-pairing of electrons in adjacent cavities predominates below 400 K. These two electrides also differ in their electrical conductivity by nearly 10 orders of magnitude. The pronounced effect of defects on conductivity and on thermonic electron emission suggests that holes as well as electrons play important roles. Now that thermally stable organic electrides can be made, it should be possible to control the electron-hole ratio by incorporation of neutral complexant molecules. We expect that in further syntheses researchers will elaborate the parent aza-cryptands to produce new organic electrides. The promise of electrides as new electronic materials with low work functions led us and others to search for inorganic electrides. The body of extensive research studies of alkali metal inclusion in the pores of alumino-silicate zeolites provided the background for our studies of pure silica zeolites as hosts for M(+) and e(-) and our later use of nanoporous silica gel as a carrier of high concentrations of alkali metals. Both systems have some of the characteristics of inorganic electrides, but the electrons and cations share the same space. In 2003, researchers at the Tokyo Institute of Technology synthesized an inorganic electride that has separated electrons and countercations. This thermally stable electride has a number of potentially useful properties, such as air-stability, low work function, and metallic conductivity. Now that both organic and inorganic electrides have been synthesized, we expect that experimental and theoretical research on this interesting class of materials will accelerate.