Mechanism of photo-oxidation of an elastomer

Ultraviolet irradiation in air of various elastomeric substances results in crosslinks, chain scissions and oxidation functions. The quantum yields of the different processes and the oxygen balance have been determined in the case of a model system. These results make it possible to propose a mechanism of photo-oxidation which agrees well with the experimental data. The rôle played by hydroperoxide functions has been recognised and demonstrated; their sensitised generation and decomposition have been explained in terms of energy transfer phenomena. Lastly, changes in the macromolecular chains and network formation have been followed. The results demonstrate quantitatively how light energy is absorbed by impurity in a polymer and is transferred to potential radical sites (hydroperoxides). Chain radical reactions develop in the material, leading predominantly to photocrosslinking simultaneously with a chain scission process which allows spatial reorganisation of the polymer medium.     

Determination de l'enthalpie de formation standard du tetrafluorure de tellure par calorimetrie de combustion dans le fluor et par calorimetrie de reaction

The standard enthalpy of formation of tellurium tetrafluoride has been determined: by combustion in fluorine:

by reaction in a normal solution of soda:

     

Multifunctional Redox Polymers: Electrochrome,Polyelectrolyte, Sensor,Electrode Modifier,Nanoparticle Stabilizer,and Catalyst Template

Simple “click” polycondensation metallopolymers of redox‐robust bis(ethynyl)biferrocene (biFc) and di(azido) poly(ethylene glycol) (PEG400 and PEG1000) were designed for multiple functions including improvement of water solubility and biocompatibility, the introduction of mixed valency and sensing capabilities, and as nanoparticle stabilizers for catalysis.     

Continuous transition from 3D to 1D confinement observed during the formation of CdSe nanoplatelets

We study the formation of colloidal CdSe nanoplatelets using both tansmission electron microscopy (TEM) and spectroscopic analysis. We show that the platelets form by continuous lateral extension of small (<2 nm) nanocrystal CdSe seeds. The nanoplatelet thickness is fixed by the seed dimension and remains constant during the platelet formation. The nanoplatelet lateral dimensions can be tuned using additional precursor injection. Absorption and fluorescence analysis of the CdSe nanoplatelets as they continuously extend laterally confirms a continuous transition from 3D to 1D confined nanoparticles. The formation of the CdSe platelets is found to be similar for different platelet thicknesses that we control with a precision of one CdSe monolayer.     

Characterization and purification of polyunsaturated fatty acids from microalgae by gas chromatography-mass spectrometry and countercurrent chromatography

Summary The present study was undertaken in order to characterize then to purify fatty acids from marine phytoplankton. From a crude mixture of fatty acid methyl esters it was possible to isolate by countercurrent chromatography a mixture of four polyunsaturated fatty acid methyl ester identified as being hexadecatrienoic acid methyl ester, octadecatetraenoic acid methyl ester, eicosapentaenoic acid methyl ester and docosahexaenoic acid methyl ester by gas chromatography coupled with mass spectrometry in electron impact and in positive-ion chemical ionization mode. The four polyunsaturated fatty acids are in different ratios in mixtures from the two microorganisms:Skeletonema costatum andIsochrysis galbana.     

LiMSO(4)F (M = Fe, Co and Ni): promising new positive electrode materials through the DFT microscope

A theoretical study of the lithium intercalated LiMSO(4)F and deintercalated MSO(4)F systems, where M = Fe, Co and Ni has been performed within the framework of density functional theory. Beyond predictions of structural evolution and average voltages versus a lithium electrode, we have applied partial density of states and Bader's topological analysis of the electron density to the study of lithium deintercalation. Upon lithium extraction, charge rearrangement occurs for nickel between different d-orbitals, but with little net positive charge gain, while cobalt and iron atoms end up with a clear oxidized state. The participation of oxygen ions in accepting the electron of the lithium is thus enhanced for LiNiSO(4)F. However, this effect does not affect the long-range electrostatic interactions a lot in the lithiated phase, since the valence of all transition metals is very close due to initial lower oxidized state for the Ni atom in the host. It is found that this is not essentially a long-range electrostatic interaction within the lithiated phase but within the host which explains, at least partly, the increase in voltage by passing from Fe to Ni. Our results also shed light upon the possibility of getting an approximate evaluation of the local strain associated with delithiation from the atomic volume evolutions, which are also likely to affect the electrochemical potential.     

Free energy landscapes for the thermodynamic understanding of adsorption-induced deformations and structural transitions in porous materials

Soft porous crystals are flexible metal-organic frameworks that respond to physical stimuli such as temperature, pressure, and gas adsorption by large changes in their structure and unit cell volume. While they have attracted a lot of interest, molecular simulation methods that directly couple adsorption and large structural deformations in an efficient manner are still lacking. We propose here a new Monte Carlo simulation method based on non-Boltzmann sampling in (guest loading, volume) space using the Wang-Landau algorithm, and show that it can be used to fully characterize the adsorption properties and the material's response to adsorption at thermodynamic equilibrium. We showcase this new method on a simple model of the MIL-53 family of breathing materials, demonstrating its potential and contrasting it with the pitfalls of direct, Boltzmann simulations. We furthermore propose an explanation for the hysteretic nature of adsorption in terms of free energy barriers between the two metastable host phases.     

Prescribing the Jacobian in critical spaces

We consider the Sobolev space $X = W^{s,p} \left( {\mathbb{S}^m ;\mathbb{S}^{k - 1} } \right)$ . We prove the existence of a robust distributional Jacobian Ju for u ∈ X, provided sp ≥ k ? 1; this generalizes a result of Bourgain, Brezis, and the second author [10] dealing with the case m = k. We identify the image of the map X ? u ? Ju in the critical case sp = k ? 1. This extends a result of Alberti, Baldo, and Orlandi [2] for s = 1 and p = k ? 1. We also present a new, analytical, dipole construction method.     

A higher order Finite Volume resolution method for a system related to the inviscid primitive equations in a complex domain

We construct the cell-centered Finite Volume discretization of the two-dimensional inviscid primitive equations in a domain with topography. To compute the numerical fluxes, the so-called Upwind Scheme (US) and the Central-Upwind Scheme (CUS) are introduced. For the time discretization, we use the classical fourth order Runge–Kutta method. We verify, with our numerical simulations, that the US (or CUS) is a robust first (or second) order scheme, regardless of the shape or size of the topography and without any mesh refinement near the topography.