Formation of TiO2 nanoparticles in water-in-CO2 microemulsions

Titanium dioxide nanoparticles can be produced by the controlled hydrolysis of titanium tetraisopropoxide in water-in-CO2 (w/c) microemulsions stabilized with the surfactants ammonium carboxylate perfluoropolyether (PFPE-NH4) and poly(dimethyl amino ethyl methacrylate-block-1H,1H,2H,2H-perfluorooctyl methacrylate) (PDMAEMA-b-PFOMA); the greater control of hydrolysis and particle growth with PDMAEMA-b-PFOMA is consistent with the differences in the stabilities and interactions for these two microemulsions.     

Elliptic equations with critical exponent on S3: new non-minimising solutions

Consider the problem:

$\{\begin{array}{cc}?{\Delta }_{S^3}U=\lambda U+U^5\text{,}U>0\hfill & \text{on?}{B}^{\prime }\text{,}\hfill \\ U=0\hfill & \text{on?}?B^{\prime }\text{,}\hfill \end{array}$

where $B^{\prime }$ is a ball on ${\mathbf{S}}^3$ with geodesic radius ${\theta }_1$, and ${\Delta }_{S^3}$ is the Laplace–Beltrami operator on ${\mathbf{S}}^3$. We prove that for any ${\theta }_1\in (\pi /2\text{,}\pi )$ and any $k>1$, there exist at least 2k solutions of this problem for λ sufficiently large negative. To cite this article: H. Brezis, L.A. Peletier, C. R. Acad. Sci. Paris, Ser. I 339 (2004).     

Photodestruction intermediates probed by an adjacent reporter molecule

We used a fluorescence resonance energy transfer donor molecule to probe the multiple intermediates in the photoinduced destruction of an acceptor molecule. These intermediates are nonemitting but are still able to quench the fluorescence of the donor at a distance scale shorter than conventional fluorescence resonance energy transfer, suggesting novel biophysical applications.     

Configurational analysis of chiral acids as O-trifluoroacetylated (-)-menthyl esters by achiral dual-capillary column gas chromatography

The simultaneous enantiomeric separation of 30 racemic acids including 24 hydroxy acids in a single analysis is described for the determination of their absolute configurations. It involves the conversion of each enantiomer into diastereomeric O-trifluoroacetylated (-)-menthyl ester for the direct separation by gas chromatography on achiral dual-capillary columns of different polarities, with subsequent identification and chiral discrimination by retention index (I) library matching. Among the acids studied, the enantiomers of 27 acids were discriminatively resolved on both non-polar DB-5 and the intermediate-polar DB-17 columns with resolution factors in the range of 0.7-7.7 and separation factors in the range of 1.002-1.021. Enantiomers of 3-hydroxybutyric and alpha-methoxyphenylacetic acids were partially resolved on DB-5 (resolution factor of 0.9), but not resolved on DB-17, while the baseline resolution for 3-hydroxydecanoic acid and the minimal separation on the peak top (resolution factor less than 0.7) for 2-hydroxyglutaric acid were achieved on DB-17 but not on DB-5. The temperature-programmed I values measured on both columns were characteristic of each enantiomer and thus simple I matching with the reference values was useful in cross-checking for their chemical identification and the chiral discrimination as well. When applied to a clinical urine sample, the present method allowed positive identification of endogenous (S)-lactic acid and (S)-2-hydroxybutyric acid along with (R)-3-hydroxybutyric acid.     

Rate and product studies in the solvolyses of methanesulfonic anhydride and a comparison with methanesulfonyl chloride solvolyses

The specific rates of solvolysis of methanesulfonic anhydride have been measured conductometrically at ?10 °C in 41 solvents. Use of the extended Grunwald–Winstein equation, with the N_T scale of solvent nucleophilicity and the Y_OTs scale of solvent ionizing power, leads to sensitivity to changes in solvent nucleophilicity (? value) of 0.95 and a sensitivity to changes in solvent ionizing power (m value) of 0.61, with a multiple correlation coefficient (R) of 0.973. Product selectivity values (S) in binary hydroxylic solvents favor alcohol attack in EtOH–H₂O (a value of 1.2 in 90% EtOH rising to 4.0 in 40% EtOH) and in MeOH–H₂O (a value of 3.7 in 90% MeOH rising to 6.0 in 50% MeOH). In 2,2,2,‐trifluoroethanol–H₂O, the S values are much lower at about 0.1. Entropy of activation values are appreciably negative. Literature values for the specific rates of solvolysis of methanesulfonyl chloride have been extended to fluoroalcohol‐containing solvents (titrimetric method) and, at 45.0 °C, for an overall 43 solvents values are obtained (using N_T and Y_C1 scales) of 1.20 for ? and of 0.52 for m (R = 0.969). It is proposed that both substrates solvolyze by an S_N2 pathway. Copyright © 2007 John Wiley & Sons, Ltd.     

Hot filament effects on CVD of carbon nanotubes

We grew vertically aligned CNTs via HFCVD using mixtures of methane and hydrogen as feedstock, and investigated the dependence of CNT growth on feedstock composition, filament temperature, and filament types. At the filament temperature of 2050 °C tungsten filaments were more efficient for CNT growth than tantalum ones, and higher CNT growth rates were observed when tungsten filaments were operated at 1900 °C. Regardless of filament temperatures and types, monotonic increase in growth rate of vertically aligned CNTs was observed as we increased the methane concentration in the feedstock. In‐situ investigation of feedstock dissociation revealed the generation of various radical species, and, moreover, a strong correlation between CNT growth rates and relative mole fractions of single‐carbon radicals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Alloying of cold-sprayed Al-Ni composite coatings by post-annealing

A new cold spray coating technique for thick Al coating with finely dispersed Al-Ni intermetallic compounds was tested. For easy powder preparation and high yield, rather than using of Al/compound mixture feed stock, the spraying of pure Al and Ni powders mixture followed by post-annealing was suggested. The powder composition of Al and Ni was 75:25, and 90:10 (wt.%) to expect full consumption of pure Ni into intermetallic compounds. After Al-Ni composite coatings, the Ni particles were finely dispersed and embedded in the Al matrix with a good coating yield. Above 450 °C of post-annealing temperature, the Al₃Ni and Al₃Ni₂ phases were observed in the cold-sprayed Al-Ni coatings. The Ni particles in the Al matrix were fully consumed via compounding reaction with Al at 550 °C of the annealing temperature.