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An inexpensive, facile, and high throughput synthesis of silicon nanoparticles was achieved by the mechano-chemical reduction reaction of magnesium silicide (Mg 2 Si) and silicon monoxide (SiO) using a high energy mechanical milling (HEMM) technique followed by acid leaching. Characterization of the resultant product using X-Ray diffraction, Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and surface area analyses was performed at various stages of the synthesis process. XRD patterns show that the final product formed is single phase silicon and the nanocrystalline nature was confirmed by the shifted transverse optical (TO) band, characteristic of nc-Si determined by Raman analysis. SEM and TEM shows the presence of particles of different sizes in the range of few nanometers to agglomerates of few microns which is consistent with products obtained from mechanical milling. BET measurements show a very high specific surface area (SSA) of ~190 m 2 /g obtained due to acid leaching which is also validated by the porous nature of the particles confirmed by the SEM images.

The buffering effect of carbon on the structural stability of amorphous silicon films, used as an anode for lithium ion rechargeable batteries, has been studied during long term discharge/charge cycles. To this extent, the electrochemical performance of a prototype material consisting of amorphous Si thin film (∼250 nm) deposited by radio frequency magnetron sputtering on amorphous carbon (∼50 nm) thin films, denoted as a -C/Si, has been investigated. In comparison to pure amorphous Si thin film ( a -Si) which shows a rapid fade in capacity after 30 cycles, the a -C/Si exhibits excellent capacity retention displaying ∼0.03% fade in capacity up to 50 cycles and ∼0.2% after 50 cycles when cycled at a rate of 100 μA/cm 2 (∼C/2) suggesting that the presence of thin amorphous C layer deposited between the Cu substrate and a -Si acts as a buffer layer facilitating the release of the volume induced stresses exhibited by pure a -Si during the charge/discharge cycles. This structural integrity combined with microstructural stability of the a -C/Si thin film during the alloying/dealloying process with lithium has been confirmed by scanning electron microscopy (SEM) analysis. The buffering capacity of the thin amorphous carbon layer lends credence to its use as the likely compliant matrix to curtail the volume expansion related cracking of silicon validating its choice as the matrix for bulk and thin film battery systems.

Suspensions of ZnO nanoparticles in water were prepared with the two-step powder dispersion process using several methods of ultrasonication. The dispersion of ZnO was found to proceed by a fragmentation process, with minimum achievable particle size in the range 50 to 300 nm. This is consistent with other oxide nanopowder systems, in which most primary particulates still remain in hardened aggregates that cannot be further reduced. A submersible accelerometer probe was developed and used to measure the relative ultrasonic energy field in the liquid for the various ultrasonication methods. Oscillation at the expected frequencies was identified in each case, with strong variability at different locations in the liquid volume.

The growth kinetics of WSi2 coating formed by chemical vapor deposition (CVD) of Si on a W substrate at temperatures between 1000 and 1200 °C using SiCl4–H2 gas mixtures was investigated and its isothermal oxidation resistance in 80% Ar–20% O2 atmosphere was evaluated at temperatures between 800 and 1300 °C. WSi2 coating grew with a parabolic rate law after an initial incubation period, indicating the diffusion-controlled growth. The activation energy for growth of WSi2 coating was about 42.5 kcal/mol. The isothermal oxidation rate of WSi2 coating increased with increasing oxidation temperature but rapidly decreased at 1300 °C. The oxidation product of WSi2 coating was composed of the WO3 particles embedded in the amorphous SiO2 matrix at below 1200 °C but consisted of only SiO2 phase at 1300 °C. The fast oxidation behavior of WSi2 coating at below 1200 °C was attributed to the formation of many cracks and pores, i.e. short-circuit diffusion path of oxygen, within the oxide scale, which resulted from the internal stress generated both by the large volume expansion caused by the oxidation reactions of WSi2 and by the evaporation of WO3 phase. The slow oxidation behavior of WSi2 coating at 1300 °C was due to the exclusive formation of a slow-growing continuous SiO2 scale by the rapid evaporation of WO3 phase.

This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or "nanofluids," was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (�10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise. � 2009 American Institute of Physics.

We present the steady-state and time-resolved photoluminescence (PL) spectra of poly(p-phenylenevinylene)derivatives, which exhibit a marked dependence on the side chains attached to the main chain...

Two copolymers of poly(p-phenylenevinylene) (PPV) containing low levels (0.8 and 3.6 mole %) of the 2,3,5,6-tetramethyl-I 4-phenylenevinylene (TMPV) units were prepared via the sulfonium salt precursor route, The luminescence properties of the two copolymers were studied in detail mainly for photoluminescence (PL) and electroluminescence (EL) characteristics in comparison with those of PPV itself. Inclusion of low levels of TMPV units improves EL efficiency by more than 10 times when a single layer device was constructed using ITO coated glass anode and aluminum metal cathode. This was explained by the possible partial disruption of main chain π-conjugation by the TMPV units which force its phenylene or vinylene structure to twist out of the coplanar structure in order to avoid of the steric repulsion between the methyl and vinyl protons in the TMPV units. The UV-vis, PL and EL spectra of the copolymers support this supposition.

New, wholly aromatic polyesters carrying 9,10-diphenylanthracene fluorophores along the main chain or both in the pendent and main chain were prepared and their properties were studied by differential scanning calorimetry, wide-angle X-ray diffractometry and fluorometry in solution as well as in thin solid films. The diphenylanthracene pendent groups are attached to the terephthaloyl unit of the aromatic polyester main chains through the oxyhexamethyleneoxy spacer. Two of the polymers were found to be thermotropic and all of the polymers exhibited relatively strong photoluminescence in solution as well as in thin films. Their fluorescence behavior is discussed in relation to their structures. When the diphenylanthracene fluorophores exist either both in the main chain and the side chain or only in the side chain, the polyesters reveal photoluminescence over a broad range of wavelength from 400 to about 700 nm with the maximum emitting intensity at about 450 nm. The polymer that contains the same fluorophore only in the main chain, however, shows a rather sharp luminescence from about 420 to 550 nm, although its maximum emitting intensity is observed at the same wavelength (ca. 450 nm) as for other polyesters.

Photo- (PL) and electroluminescence (EL) properties of three different PPV derivatives carrying the 9,10-diphenylanthracene units are compared. One (polymer 1) of the polymers contains the 9,10-diphenylanthracene structure as an integral part of the main chain, but the other two have it as the pendent group attached to the main chain through either oxyethyleneoxy (polymer 2) or oxyhexamethyleneoxy (polymer 3) spacer. Polymers 1 and 2 exhibit very similar PL and EL spectra that are more or less of superimposed feature of the spectra from the backbones and the anthracene pendents. In contrast, polymer 3 shows an EL spectrum that is completely different from its PL spectrum. Whereas the PL spectrum of polymer 3 appears to be a combination of the spectra from the main chain and the pendents, as for polymer 1 and 2, the EL spectrum of polymer 3, however, looks as if the lights were emitted only from the backbone. This difference is explained in terms of excited state electronic interactions between the main chain and the pendents.

A series of new wholly aromatic polyesters was synthesized by melt polycondensation of 1-phenyl-2,6-naphthalenedicarboxylic acid (PNDA) and diacetates of various aromatic diols. The aromatic diols studied are hydroquinone (HQ), methylhydroquinone (MHQ), phenylhydroquinone (PHQ), (α-phenylisopropyl)hydroquinone (PIHQ), 2,6-naphthalenediol (2,6-ND), 1,4-naphthalenediol (1,4-ND), and 4,4′-biphenol (BP). These polyesters were characterized for their crystallinity, glass transition temperature (Tg), melting temperature (Tm), liquid crystallinity, and thermal stability. In general, crystallinity of the polyesters are very low and the Tg values of the polyesters range from 150 to 172°C depending on the structure of aromatic diols. All of the polymers formed nematic phases above their Tm or Tg. The polyesters derived from PHQ and PIHQ are soluble in chlorinated hydrocarbon solvents. The initial decomposition temperatures of the polyesters are above 400°C under N2 atmosphere. © 1996 John Wiley & Sons, Inc.

Two different series of new aromatic liquid crystalline (LC) polyesters were prepared from 3-phenyl-4, 4'-biphenyldicarboxylic acid (PBDA) and 1-phenyl-2, 6-naphthalenedicarboxylic acid (PNDA). PBDA and PNDA were polymerized with various aromatic diols such as hydroquinone, substituted hydroquinones, isomeric naphthalenediols and 4, 4'-biphenol, and the resulting polyesters were characterized by DSC, WAXD, and on a cross-polarizing microscope for the study of their thermal transition and crystallization properties, and mesophases formed therefrom.

A chromophore in which zinc porphyrin donors are linked through their meso positions by ethynyl bridges to a bis(indolinylidenemethyl) squaraine core has been synthesized using Sonogashira coupling. The chromophore exhibits a two-photon absorption spectrum characterized by a peak cross section of 11,000 GM and, more unusually, also exhibits a large cross section of >780 GM over a photon-wavelength window 750 nm in width.

We have developed a novel integrated supramolecular device for a photosynthetic antenna/reaction center (RC) model based on a helical amylose, which plays an important role as the host for cyanine dye J-aggregation onto the helical surface and also for inclusion of a D−A chain chromophore inside the helical cavity, where the J-aggregates function as an array of photoreceptor antenna that funnel excitation across the helix to the chromophore.

(E)-4,4'-Bis[bis(4-methoxyphenyl)amino]stilbene, 1, (E,E)-1,4-bis[4-[bis(4-methoxyphenyl)amino]styryl]benzene, 2, and two longer homologues, (E,E,E)-4,4'-bis[4-[bis(4-methoxyphenyl)amino]styryl]stilbene, 3, and (E,E,E,E)-1,4-bis(4-[4-[bis(4-methoxyphenyl)amino]styryl]styryl)benzene, 4, have been oxidized to their mono- and dications using tris(4-bromophenyl)aminium hexachloroantimonate. The intervalence charge-transfer (IVCT) band of 1(+) is narrow and asymmetric and exhibits only weak solvatochromism. Analysis of this band indicates that 1(+) is a class-III or class-II/III borderline mixed-valence species. In contrast, a broad, strongly solvatochromic IVCT band is observed for 2(+), indicating that this species is a class-II mixed-valence species. The assignment of 1(+ ) and 2(+) as symmetric class-III and unsymmetric class-II species, respectively, is also supported by AM1 calculations. Hush analysis of the IVCT bands of both 1(+) and 2(+) gives larger electronic couplings, V, than for their analogues in which the double bonds are replaced with triple bonds. The diabatic electron-transfer distance, R, in 1(+) can be estimated by comparison of the V estimated by Hush analysis and from the IVCT maximum; it is considerably less than the geometric N-N separation, a result supported by quantum-chemical estimates of R for 1(+)-4(+). In 3(+) and 4(+), the IVCT is largely obscured by an intense absorption similar to a band seen in the corresponding dications and to that observed in the monocation of a model compound, (E,E,E)-1-[bis(4-methoxyphenyl)amino]-4-[4-[4-(4-tert-butylstyryl)styryl]styryl]benzene, 5, containing only one nitrogen redox center; we attribute this band to a bridge-to-N(+) transition. The corresponding dications 1(2+)-4(2+) show a complementary trend in the coupling between redox centers: the shortest species is diamagnetic, while the dication with the longest bridge behaves as two essentially noninteracting radical centers.

Identification and development of non-noble metal based electro-catalysts or electro-catalysts comprising compositions with significantly reduced amounts of expensive noble metal contents (e.g. IrO2, Pt) with comparable electrochemical performance to the standard noble metal/metal oxide for proton exchange membrane (PEM) based water electrolysis would signify a major breakthrough in hydrogen generation via water electrolysis. Development of such systems would lead to two primary outcomes: first, a reduction in the overall capital costs of PEM based water electrolyzers, and second, attainment of the targeted hydrogen production costs (

The decay dynamics of photoexcited poly[(2-carbazol)-p-phenylene-vinylene](PCzPV) and poly[(2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3, 4-oxadiazole) -p-phenylenevinylene](PPPDPV) were investigated. The cw photoluminescence spectrum of PCzPV is composed of well-resolved two emission bands and a weak but apparent emission band at much lower energy. On the other hand, PPPDPV exhibits a broad and featureless emission band. The photoluminescence decay PPPDPV is almost independent of excitation energy and temperature. However, when the side chain substituent is changed to carbazole, the overall decay dynamics strongly depend on the excitation wavelength as well as temperature. The decay time constant at 580 nm of photoexcited PCzPV is shortened with a change in the excitation energy from 400 nm to 300 nm at 13 K. These results in the PCzPV and PPPDPV are interpreted in terms of the electronic properties of substituent and excimer process between substituent and main chain.

With increasing pressure on engine oil manufacturers to extend oil drain intervals and reduce fuel consumption, whilst changing the composition of fully formulated oils to meet the new CEC, ILSAC and OEM specifications, there is an ever increasing need to understand the effect of oil degradation on the operating conditions and tribological performance of engines [1]. This work samples oil from the rear of the top piston ring of an engine during the first 15 minutes from cold start and operating at steady state under three different loads. These samples, used 40 hour sump oil and fresh oil have been subjected to tribological tests and chemical analysis.Copyright © 2005 by The University of Leeds and The University of York