Negative field-dependent charge mobility in crystalline organic semiconductors with delocalized transport

Charge-carrier mobility has been investigated by time-of-flight (TOF) transient photocurrent in a lateral transport configuration in highly crystalline thin films of 2,7-dioctyl[1]benzothieno [3,2-b][1] benzothiophene (C₈-BTBT) grown by a zone-casting alignment technique. High TOF mobility has been revealed that it is consistent with the delocalized nature of the charge transport in this material, yet it featured a positive temperature dependence at \( T \ge 295\,{\text{K}} \). Moreover, the mobility was surprisingly found to decrease with electric field in the high-temperature region. These observations are not compatible with the conventional band-transport mechanism. We have elaborated an analytic model based on effective-medium approximation to rationalize the puzzling findings. The model considers the delocalized charge transport within the energy landscape formed by long-range transport band-edge variations in imperfect organic crystalline materials and accounts for the field-dependent effective dimensionality of charge transport percolative paths. The results of the model calculations are found to be in good agreement with experimental data.     

Characterisation and deployment of an immobilised pH sensor spot towards surface ocean pH measurements

The oceans are a major sink for anthropogenic atmospheric carbon dioxide, and the uptake causes changes to the marine carbonate system and has wide ranging effects on flora and fauna. It is crucial to develop analytical systems that allow us to follow the increase in oceanic pCO₂ and corresponding reduction in pH. Miniaturised sensor systems using immobilised fluorescence indicator spots are attractive for this purpose because of their simple design and low power requirements. The technology is increasingly used for oceanic dissolved oxygen measurements.     

Observations on the Hantzsch Reaction: Synthesis of N-tBoc-S-Dolaphenine

An understanding of the mechanism by which racemization occurs in the Hantzsch reaction preparation of 2-(1-aminoalkyl)thiazoles has enabled the development of a methodology to prevent racemization. N-^tBoc-S-dolaphenine (3) is then synthesized using this methodology.     

Numerical prediction of turbulent flows using Reynolds‐averaged Navier–Stokes and large‐eddy simulation with uncertain inflow conditions

Numerous comparisons between Reynolds‐averaged Navier–Stokes (RANS) and large‐eddy simulation (LES) modeling have already been performed for a large variety of turbulent flows in the context of fully deterministic flows, that is, with fixed flow and model parameters. More recently, RANS and LES have been separately assessed in conjunction with stochastic flow and/or model parameters. The present paper performs a comparison of the RANS k ? ε model and the LES dynamic Smagorinsky model for turbulent flow in a pipe geometry subject to uncertain inflow conditions. The influence of the experimental uncertainties on the computed flow is analyzed using a non‐intrusive polynomial chaos approach for two flow configurations (with or without swirl). Measured quantities including an estimation of the measurement error are then compared with the statistical representation (mean value and variance) of their RANS and LES numerical approximations in order to check whether experiment/simulation discrepancies can be explained within the uncertainty inherent to the studied configuration. The statistics of the RANS prediction are found in poor agreement with experimental results when the flow is characterized by a strong swirl, whereas the computationally more expensive LES prediction remains statistically well inside the measurement intervals for the key flow quantities.Copyright © 2012 John Wiley & Sons, Ltd.     

May Trifluoromethylation and Polymerization of Styrene Occur from a Perfluorinated Persistent Radical (PPFR)?

The radical polymerization of styrene (St) initiated by a trifluoromethyl radical generated from a perfluorinated highly branched persistent radical (PPFR) is presented with an isolated yield above 70 %. The release of ^.CF₃ radical occurred from a temperature above 85 °C. Deeper ¹H and ¹⁹F NMR spectroscopies of the resulting fluorinated polystyrenes (CF₃-PSts) evidenced the presence of both CF₃ end-group of the PSt chain and the trifluoromethylation of the phenyl ring (in meta-position mainly). [PPFR]₀/[St]₀ initial molar ratios of 3:1, 3:10 and 3:100 led to various molar masses ranging from 1750 to 5400 g mol⁻¹ in 70–86 % yields. MALDI-TOF spectrometry of such CF₃-PSts highlighted polymeric distributions which evidenced differences between m/z fragments of 104 and 172 corresponding to styrene and trifluoromethyl styrene units, respectively. Such CF₃-PSt polymers were also compared to conventional PSts produced from the radical polymerization of St initiated by a peroxydicarbonate initiator. A mechanism of the polymerization is presented showing the formation of a trifluoromethyl styrene first, followed by its radical (co)polymerization with styrene. The thermal properties (thermal stability and glass transition temperature, T_g) of these polymers were also compared and revealed a much better thermal stability of the CF₃-PSt (10 % weight loss at 356–376 °C) and a T_g of around 70 °C.     

Homogeneous dispersion of gadolinium oxide nanoparticles into a non-aqueous-based polymer by two surface treatments

Gadolinium oxide nanoparticles are more and more used. They can notably provide interesting fluorescence properties. Herein they are incorporated into a non-aqueous-based polymer, the poly(methyl methacrylate). Their dispersion within the polymer matrix is the key to improve the composite properties. As-received gadolinium oxide nanopowders cannot be homogeneously dispersed in such a polymer matrix. Two surface treatments are, therefore, detailed and compared to achieve a good stability of the nanoparticles in a non-aqueous solvent such as the 2-butanone. Then, once the liquid suspensions have been stabilized, they are used to prepare nanocomposites with homogeneous particles dispersion. The two approaches proposed are an hybrid approach based on the growth of a silica shell around the gadolinium oxide nanoparticles, and followed by a suitable silane functionalization; and a non-hybrid approach based on the use of surfactants. The surface treatments and formulations involved in both methods are detailed, adjusted and compared. Thanks to optical methods and in particular to the use of a ??home made?? confocal microscope, the dispersion homogeneity within the polymer can be assessed. Both methods provide promising and conclusive results.     

Palladium Catalysed Tandem Allylic Substitution Methodology in the Synthesis of a Component of Civet

A facile synthesis of a component of civet 1 is reported in which the key step involves palladium catalysed introduction of the acetic acid substituent in the C-1 position of a pseudorhamnal derivative.     

Design,fabrication and evaluation of a low-cost homogeneous portable permanent magnet for NMR and MRI

We propose a magnet featuring a standard 52 mm bore that creates a longitudinal magnetic field. The magnet is made out of commercial magnetized NdFeB cubes, costing less than 100 €. This device is a low-cost solution to build a portable magnet generating a field of 100 mT with an intrinsic homogeneity as good as 40 ppm over a 5 mm³ volume. Furthermore, the bore can accomodate a standard narrow bore shim stack and NMR probe in order to shim the field and conduct low-field NMR experiments. We established an assembly process including characterization of the magnetic cubes, cube sorting and optimization of the assembly according to the needs of the application. Aspects of the assembly method are discussed, including characterizing the magnet cubes, sorting them and arranging them in an optimal fashion.     

Alternative Syntheses of L-(-)-Oleandrose from L-Rhamnose1 Preparation of Glycals

L-Rhamnal (2) is prepared from L-rhamnose (3) by use of an improved generalized Fischer-Zach reaction. L-Rhamnal (2) is then converted to L-(-)-oleandrose (1) by stannylene mediated selective methylation and effective hydration. Benzyl α-L-oleandrose (12) is prepared by selective methylation and deoxygenation of L-rhamnose (3).