Small strain behavior of polyethylene: In situ SAXS measurements

Stack lamella deformation depends on their orientation with respect to the loading axis, the intrinsic properties of the lamellae, and the mechanical coupling between crystalline and amorphous phases. The aim of this work is to investigate the influence of the stress transmitter (ST) density and the crystallinity X_c on the local deformation. A wide experimental campaign has been undertaken on several polyethylenes with controlled molecular parameters and subjected to different thermal treatments. The ST density has been evaluated by the natural draw ratio and calculated by the Brown's model. The local deformation was measured by SAXS along a tensile test by using the long period stretching of the equatorial lamella stacks. The ratio ε_local/ε_macro was found to be a constant close to 0.5. This surprising low value has highlighted that the equatorial regions could be either the stiffest zone of the spherulite or submitted to a lower stress. It is proposed that the stability of the ratio ε_local/ε_macro is the result of two opposite phenomena: On one hand, the increase of X_c leads to unload the equatorial regions due to partial percolation of the crystalline phase and so decreases the stresses. On the other hand, when increasing X_c, the ST density decreases which causes the decrease in the local equatorial modulus. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1535–1542, 2010     

Photoinduced electron transfer in Zn(II)porphyrin-bridge-Pt(II)acetylide complexes: variation in rate with anchoring group and position of the bridge

The synthesis and photophysical characterization of two sets of zinc porphyrin platinum acetylide complexes are reported. The two sets of molecules differ in the way the bridging phenyl-ethynyl unit is attached to the porphyrin ring. One set is attached via an ethynyl unit on the β position, while the other set is attached via a phenyl unit on the meso position of the porphyrin. These were compared with previously studied complexes where attachment was made via an ethynyl unit on the meso position. Femtosecond transient absorption measurements showed in all systems a rapid quenching of the porphyrin singlet state. Electron transfer is suggested as the quenching mechanism, followed by an even faster recombination to form both the porphyrin ground and triplet excited states. This is supported by the variation in quenching rate and porphyrin triplet yield with solvent polarity, and the observation of an intermediate state in the meso-phenyl linked systems. The different linking motifs between the dyads resulted in significant variations in electron transfer rates.     

Phosphorus dendrimers as viewed by 31P NMR spectroscopy; synthesis and characterization

This review emphasizes the role of phosphorus for the elaboration of dendrimers and of various highly sophisticated dendritic structures, and the invaluable role played by ³¹P NMR for their characterization and to ascertain their purity. A few properties, highlighting the importance of phosphorus are reported at the end of this review.     

Thermosensitive graphene nanocomposites formed using pyrene‐terminal polymers made by RAFT polymerization

Thermosensitive graphene‐polymer composites have been prepared by attaching poly(N‐isopropylacrylamide) (PNIPAAm) onto the basal plane of graphene sheets via π‐π stacking. Pyrene‐terminated PNIPAAm was synthesized using reversible addition fragmentation chain transfer (RAFT) polymerization via a pyrene‐functional RAFT agent. Aqueous solutions of the graphene‐polymer composites were stable and thermosensitive. The lower critical solution temperature (LCST) of pyrene‐terminated PNIPAAm was measured to be 33 °C. When the pyrene‐functional polymer was attached to graphene the resultant composites were also thermosensitive in aqueous solutions exhibiting a reversible suspension behavior at 24 °C. Atomic force microscopy (AFM) analysis revealed that the thickness of a graphene‐PNIPAAm (M_n: 10,000 and PDI: 1.1) sheet was ～5.0 nm. The surface coverage of polymer chains on the graphene basal plane was calculated to be 7.2 × 10^?11 mol cm^?2. The graphene‐PNIPAAm composite material was successfully characterized using X‐ray photoelectron spectroscopy (XPS), attenuated total reflection infrared (ATR‐IR) spectroscopy, and thermogravimetric analysis (TGA). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 425–433, 2010     

Complex interpolation between two weighted Bergman spaces on tubes over symmetric cones

We prove that the complex interpolation space [A_ν^p₀,A_ν^p₁]_θ, 0<θ<1, between two weighted Bergman spaces A_ν^p₀ and A_ν^p₁ on the tube in $\text{C}{}^{\mathrm{n}}$, n?3, over an irreducible symmetric cone of $\text{R}{}^{\mathrm{n}}$ is the weighted Bergman space A_ν^p with 1/p=(1?θ)/p₀+θ/p₁. Here, ν>n/r?1 and 1?p₀<p₁<2+ν/(n/r?1) where r denotes the rank of the cone. We then construct an analytic family of operators and an atomic decomposition of functions, which are related to this interpolation result. To cite this article: D. Békollé et al., C. R. Acad. Sci. Paris, Ser. I 337 (2003).