Preparation d'alcools acetyleniques et propargyliques F-alkyles

A number of α-β acetylenic carbinols R_FCCC(OH)RR′, in which the acetylenic proton was substituted by a F-alkyl group, were first prepared, from a classical reaction of (F-alkynyl)- lithium derivatives R_FCCLi upon various carbonyl compounds.On another hand, the reaction of propargyl bromide metallic complexes (organoaluminic, or ultrasonic irradiation activated organozinc) upon some polyfluorinated ketones R_FCOR led to the formation, in convenient yields, of the propargylic carbinols HCCCH₂C(OH)RR_F.The synthesis and properties of these series of new (F-alkyl) substituted acetylenic and propargylic alcohols are described and discussed.     

Taguchi orthogonal design assisted immobilization of Candida rugosa lipase onto nanocellulose-silica reinforced polyethersulfone membrane: physicochemical characterization and operational stability

Cellulose - A greener processing route to replace the current environmentally-unfriendly esterification technique to produce biofuels such as pentyl valerate (PeVa) was explored. This study...     

An original approach for Raman spectroscopy analysis of radioactive materials and its application to americium‐containing samples

An approach for Raman measurements of highly radioactive samples is presented here. The innovative part of this approach lies in the fact that no single part of the Raman equipment is in direct contact with the radioactive sample, as the sample is sealed in an alpha‐tight capsule. Raman analysis is effectively performed through the optical‐grade quartz window closing the capsule. This allows performing micro‐Raman measurements on radioactive samples with no limitations on the laser source wavelength, polarisation mode, spectrometer mode and microscope mode (provided the focal length of the microscope objective is greater than the thickness of the quartz window and with sub mg samples). Some example results are shown and discussed. In particular, some spectral features of americium‐containing oxide nuclear fuel specimens are presented. Raman spectra clearly reveal in these specimens the presence of abundant oxygen defects induced in the fcc fluorite lattice by trivalent americium. In order to complete the analysis the Raman spectrum of pure americium dioxide was also measured with a lower energy excitation source compared with previous research. The current results seem to be consistent with the possible occurrence of a photolysis process induced by the Raman laser, resulting in the formation of hyperstoichiometric americium sesquioxide Am₂O_{3 + z}. Such a photolytic process is deemed to be unavoidable when visible lasers are used as excitation sources for the Raman analysis of americium dioxide. © 2015 The Authors Journal of Raman Spectroscopy Published by John Wiley & Sons, Ltd.     

Non-linear osmotic brush regime: Simulations and mean-field theory

We investigate polyelectrolyte brushes in the osmotic regime using both theoretical analysis and molecular dynamics simulation techniques. In the simulations at moderate Bjerrum length, we observe that the brush height varies weakly with grafting density, in contrast to the accepted scaling law, which predicts a brush thickness independent of the grafting density. We show that such behavior can be explained by considering lateral electrostatic effects (within the non-linear Poisson-Boltzmann theory) combined with the coupling between lateral and longitudinal degrees of freedom due to the conserved polymer volume (which are neglected in scaling arguments). We also take the non-linear elasticity of polyelectrolyte chains into consideration, which makes significant effects as chains are almost fully stretched in the osmotic regime. It is shown that all these factors lead to a non-monotonic behavior for the brush height as a function of the grafting density. At large grafting densities, the brush height increases with increasing the grafting density due to the volume constraint. At small grafting densities, we obtain a re-stretching of the chains for decreasing grafting density, which is caused by lateral electrostatic contributions and is controlled by the counterion-condensation process around polyelectrolyte chains. These results are obtained assuming all counterions to be trapped within the brush, which is valid for sufficiently long chains of large charge fraction.Received: 14 May 2003, Published online: 11 November 2003PACS: 61.25.Hq Macromolecular and polymer solutions; polymer melts; swelling - 36.20.-r Macromolecules and polymer molecules - 61.20.Qg Structure of associated liquids: electrolytes, molten salts, etc.     

Growth of vertical and defect free InP nanowires on SrTiO3(001) substrate and comparison with growth on silicon

We present a study of the molecular beam epitaxy of InP nanowires (NWs) on (001) oriented SrTiO₃ (STO) substrates using vapor liquid solid mechanism and gold–indium as metal catalyst. The growth direction of InP NWs grown on STO(001) is compared with NWs grown on (001) and (111) oriented silicon substrates. Gold–indium dewetting under a flux of indium results in the majority of InP NWs growing vertically from the surface of STO(001). With the growth parameters we have used the NWs have a pure wurtzite structure and are free of stacking faults and cubic segments. The structural quality of the NWs is confirmed by micro-photoluminescence measurements showing a narrow peak linewidth of 6.5 meV.     

The hyperbolic heat conduction equation in an anisotropic material

In this work, the phase-lag concept in the wave theory of heat conduction is extended to describe the thermal behavior of anisotropic material. This is achieved by assuming that there are phase-lags of different magnitudes between each component of the heat flux vector and the summation of temperature gradients in all directions of the orthogonal coordinate system. Also, expressions are provided to specify the locations of the principal coordinate axes, the principal thermal conductivities and the principal thermal relaxation times. Received on 26 March 1999     

Dynamics of the biopolymers in articular cartilage studied by magic angle spinning NMR

To understand the viscoelastic properties of cartilage tissue and for the development of tissue-engineered cartilage, we have studied the physicochemical properties of bovine nasal and pig articular cartilage by¹³C nuclear magnetic resonance (NMR) methods. The major macromolecular components of cartilage can be investigated individually by applying¹³C high-resolution (HR) NMR with scalar decoupling (for the polysaccharide component) and solid-state NMR with dipolar decoupling (for the collagen component). Partially resolved NMR spectra of the cartilage polysaccharides can be obtained by HR¹³C NMR indicating that these polysaccharides are highly mobile. Resonance lines have been assigned to chondroitin sulfate, the most mobile component of cartilage. To characterize time scales of molecular motions, we have measuredT ₁ andT ₂ relaxation times as a function of temperature and analyzed these data by means of a broad distribution of molecular correlation times. Typical correlation times for the large amplitude motions of chondroitin sulfate are of the order of 0.1–10 ns. For the detection and dynamical characterization of the cartilage collagen cross-polarization magic angle spinning (CP MAS) and high-power decoupling are indispensable.¹³C CP MAS spectra of cartilage are dominated by resonances from rigid collagen, while only low-intensity signals from the polysaccharides are observed. The good sensitivity at a magnetic field strength of 17.6 T allows the site-specific investigation of cartilage collagen dynamics by two-dimensional NMR methods. The cartilage collagen is essentially rigid with low-amplitude segmental motions on the fast time scale. Considering the high water content of cartilage and the almost isotropic mobility of the chondroitin sulfate molecules it is remarkable how little this affects the collagen dynamics. The dynamics of cartilage macromolecules is broadly distributed from almost completely rigid to highly mobile, which lends cartilage its mechanical strength and shock-absorbing properties.     

Partially Annealed Disorder and Collapse of Like-Charged Macroions

Charged systems with partially annealed charge disorder are investigated using field-theoretic and replica methods. Charge disorder is assumed to be confined to macroion surfaces surrounded by a cloud of mobile neutralizing counterions in an aqueous solvent. A general formalism is developed by assuming that the disorder is partially annealed (with purely annealed and purely quenched disorder included as special cases), i.e., we assume in general that the disorder undergoes a slow dynamics relative to fast-relaxing counterions making it possible thus to study the stationary-state properties of the system using methods similar to those available in equilibrium statistical mechanics. By focusing on the specific case of two planar surfaces of equal mean surface charge and disorder variance, it is shown that partial annealing of the quenched disorder leads to renormalization of the mean surface charge density and thus a reduction of the inter-plate repulsion on the mean-field or weak-coupling level. In the strong-coupling limit, charge disorder induces a long-range attraction resulting in a continuous disorder-driven collapse transition for the two surfaces as the disorder variance exceeds a threshold value. Disorder annealing further enhances the attraction and, in the limit of low screening, leads to a global attractive instability in the system.     

Electrochemical investigation of gel polymer electrolytes based on poly(methyl methacrylate) and dimethylacetamide for application in Li-ion batteries

In the present work, gel polymer electrolytes (GPEs) were prepared using poly(methyl methacrylate) (PMMA), lithium perchlorate (LiClO₄) and dimethylacetamide as a plasticizer. Solution-casting technique was used to fabricate GPEs containing different weight percentage of PMMA. The degree of crystallinity of GPE samples was studied by X-ray diffraction (XRD) analysis. Fourier transform infrared (FT-IR) spectroscopy was applied to study the level of interactions between lithium salt and PMMA in the prepared GPEs. Electrochemical properties were studied by electrochemical impedance spectroscopy, linear sweep voltammetry and DC polarization techniques. Lithium ion conductivity of GPEs was determined by calculating the bulk resistance of polymer electrolytes from Nyquist plot. Increasing PMMA content of GPEs resulted in an improvement in the electrochemical potential window from 4.2 to 4.5 V. The highest lithium transference number (0.42) and also the best electrochemical properties were obtained for GPE containing 0.75 M LiClO₄ and 10 wt% PMMA. Scanning electron microscopy images of the optimized GPE showed a porous and heterogeneous surface structure which is desirable for application in Li-ion batteries.