Proximity effect on hydrodynamic interaction between a sphere and a plane measured by Force Feedback Microscopy at different frequencies

In this article, we measure the viscous damping $G'',$ and the associated stiffness $G',$ of a liquid flow in sphere-plane geometry in a large frequency range. In this regime, the lubrication approximation is expected to dominate. We first measure the static force applied to the tip. This is made possible thanks to a force feedback method. Adding a sub-nanometer oscillation of the tip, we obtain the dynamic part of the interaction with solely the knowledge of the lever properties in the experimental context using a linear transformation of the amplitude and phase change. Using a Force Feedback Microscope (FFM)we are then able to measure simultaneously the static force, the stiffness and the dissipative part of the interaction in a broad frequency range using a single AFM probe. Similar measurements have been performed by the Surface Force Apparatus with a probe radius hundred times bigger. In this context the FFM can be called nano-SFA

Out of equilibrium anomalous elastic response of a water nano-meniscus

We report the observation of a transition in the dynamical properties of water nano-menicus which dramatically change when probed at different time scales. Using a AFM mode that we name Force Feedback Microscopy, we observe this change in the simultaneous measurements, at different frequencies, of the stiffness G'(N/m), the dissipative coefficient G''(kg/sec) together with the static force. At low frequency we observe a negative stiffness as expected for capillary forces. As the measuring time approaches the microsecond, the dynamic response exhibits a transition toward a very large positive stiffness. When evaporation and condensation gradually lose efficiency, the contact line progressively becomes immobile. This transition is essentially controlled by variations of Laplace pressure

Non-Universal Quasi-Long Range Order in the Glassy Phase of Impure Superconductors

The structural correlation functions of a weakly disordered Abrikosov lattice are calculated for the first time in a systematic RG-expansion in d=4-\epsilon dimensions. It is shown, that in the asymptotic limit the Abrikosov lattice exhibits still quasi long range translational order described by a non-universal exponent \bar\eta_{\bf G} which depends on the ratio of the renormalized elastic constants \kappa =\tilde c_{66}/\tilde c_{11} of the flux line (FL) lattice. Our calculations show clearly three distinct scaling regimes corresponding to the Larkin, the manifold and the asymptotic Bragg glass regime. On a wide range of intermediate length scales the FL displacement correlation function increases as a power law with twice of the manifold roughness exponent \zeta_{rm}(\kappa), which is also non-universal. Our results, in particular the \kappa-dependence of the exponents, are in variance with those of the variational treatment with replica symmetry breaking which allows in principle an experimental discrimination between the two approaches.Comment: 4 pages, 3 figure

alpha,omega-Bis(trialkoxysilyl) difunctionalized polycyclooctenes from ruthenium-catalyzed chain-transfer ring-opening metathesis polymerization

International audienceThe ring-opening metathesis polymerization/cross-metathesis (ROMP/CM) of cyclooctene (COE) using bis(trialkoxysilyl)alkenes as chain-transfer agents (CTAs) and Ru catalysts to afford difunctionalized polyolefins is reported. The formation of alpha,omega-bis(trialkoxysilyl) telechelic polycycloolefins (DF) with controlled molar mass values takes place quite selectively (>90 wt%), along with minor amounts of cyclic non-functionalized polymers (CNF), as evidenced by NMR, MALDI-ToF MS, SEC analyses and fractionation experiments. The nature of the CTA and catalyst influenced much the efficiency and selectivity of the reaction. (MeO)(3)SiCH2CH=CHCH2Si(OMe)(3) (2) and (MeO)(3)Si(CH2)(3)NHC(O)OCH2CH=CHCH2OC(O)NH (CH2)(3)Si(OMe)(3) (5) proved to be the most efficient CTAs in terms of reactivity, catalyst productivity and selectivity towards DF. Diurethane CTA 5 is easily prepared, and can also be conveniently generated in situ during the ROMP/CM. Grubbs' 2nd-generation catalyst (G2) and Hoveyda-Grubbs's catalyst (HG2) afforded the best compromise in terms of selectivity and productivity, with turnover numbers of up to 95 000 mol(COE) mol(Ru)(-1) and 5000 mol(CTA) mol(Ru)(-1)

Formation of high-valent iron-oxo species in superoxide reductase: characterization by resonance Raman spectroscopy.

International audienceSuperoxide reductase (SOR), a non-heme mononuclear iron protein that is involved in superoxide detoxification in microorganisms, can be used as an unprecedented model to study the mechanisms of O2 activation and of the formation of high-valent iron-oxo species in metalloenzymes. By using resonance Raman spectroscopy, it was shown that the mutation of two residues in the second coordination sphere of the SOR iron active site, K48 and I118, led to the formation of a high-valent iron-oxo species when the mutant proteins were reacted with H2O2. These data demonstrate that these residues in the second coordination sphere tightly control the evolution and the cleavage of the O-O bond of the ferric iron hydroperoxide intermediate that is formed in the SOR active site

Ring-opening metathesis polymerization of cyclooctene derivatives with chain transfer agents derived from glycerol carbonate

International audienceThe synthesis of a variety of mono- and di-(glycerol carbonate) telechelic polyolefins has been achieved upon ruthenium-catalyzed ring-opening metathesis polymerization (ROMP) of cyclooctene (COE) derivatives in the presence of a vinyl or acryloyl derivative of glycerol carbonate (GC) acting as a chain-transfer agent (CTA). Reaction monitoring based on SEC and 1H NMR analyses suggested that the ROMP proceeds through the formation of first the α-GC,ω-vinyl-poly(cyclooctene) (PCOE) intermediate, which eventually evolves over time into the α,ω-di(GC)-PCOE. The nature of the solvent was shown to have a significant impact on both the reaction rates and the eventual selectivity for the mono-/di-telechelic PCOE. ROMP of 3-alkyl (methyl, ethyl, n-hexyl)-substituted COEs (3-R-COEs) afforded only the α-GC,ω-vinyl-poly(3-R-COE)s, as a result of the steric hindrance around the active intermediate, while a 5-ethyl substituted COE (5-Et-COE) enabled access to the corresponding α,ω-di(GC)-poly(5-Et-COE). The ROMP of 5,6-epoxy-, 5-hydroxy- and 5-oxo-functionalized COEs in the presence of acryloyl-GC as the CTA has also been achieved, affording from the first two monomers polymers with GC end-groups at both extremities, while a 60 : 40 mixture of mono- and di-GC terminated P(5-O[double bond, length as m-dash]COE) was observed in the latter case

α,ω-Di(glycerol carbonate) telechelic polyesters and polyolefins as precursors to polyhydroxyurethanes: an isocyanate-free approach

International audienceα,ω-Di(glycerol carbonate) telechelic poly(propylene glycol) (PPG), poly(ethylene glycol) (PEG), poly(ester ether) (PEE), and poly(butadiene) (PBD) have been synthesized through chemical modification of the corresponding α,ω-dihydroxy telechelic polymers (PPG-OH2, PEG-OH2, PEE-OH2 and PBD-OH2, respectively). Tosylation of the polymer diols with 4-tosylmethyl-1,3-dioxolan-2-one (GC-OTs) afforded, in high yields, the desired PPG, PEG, PEE and PBD end-capped at both termini with a five-membered ring cyclic glycerol carbonate (4-hydroxymethyl-1,3-dioxolan-2-one, GC). The GC-functionalization of the polymers at both chain-ends has been confirmed by NMR (1H, 13C, 1D and 2D) and FTIR spectroscopies. Using PPG-GC2 to demonstrate the concept, the corresponding polyhydroxyurethanes (PHUs/non-isocyanate polyurethanes (NIPUs)) have been subsequently prepared following a non-isocyanate method upon ring-opening catalyst-free polyaddition of the PPG-GC2 with JEFFAMINEs (Mn = 230-2000 g mol−1). The effect of various additives introduced during the polyaddition reaction has been studied at different temperatures. In particular, addition of LiBr (5 mol%) to the reaction medium was found to slightly promote the cyclocarbonate/amine reaction. The polymerization process was supported by FTIR and SEC analyses