Preparation, treatment and characterisation of nanocrystalline mesoporous ordered layers

The general approach to mesoporous ordered silica and crystalline metal oxide thin films, involving soft chemistry, liquid deposition technique, surfactant templating and tuned annealing conditions, is presented. Highly ordered cubic mesoporous structures, made of amorphous SiO₂ xerogels or nanocrystalline particles such as anatase TiO₂, γ-Al₂O₃, ilmenite CoTiO₃, or perovskite SrTiO₃ have been chosen to illustrate this article. In situ time resolved SAXS analyses, involving synchrotron high flux, were used to assess the various phenomena involved during deposition, thermal treatment and crystallisation. It will be demonstrated that the self-assembly is not only critically dependant on the structuring agent to inorganic volume fraction, but also on chemical and processing parameters such as the inorganic degree of condensation and the atmosphere applied during the deposition. A general model of self-assembly, based on a Tunable Stated State, is proposed. Concerning the crystallisation step, we will show that, depending on the heating regime, ordered mesoporous nanocrystalline framework can be obtained through a rigorous control of nucleation, growth and diffusive sintering taking successively place in the mineral matrix. Finally, the porosity and pore size distribution of these silica and non silica layers were assessed using ellipsometry porosimetry. This novel and very efficient technique provides the full characteristics of the layer porosity by measuring the variation of optical constant associated to the adsorption/desorption of a gas within the porous network.     

Complexation Studies of Phosphorus Containing Bis and Tris (Benzocrown Ether) Moieties

The complexation behaviour between salts of Li⁺-Rb⁺ in CD₃CN and tris(benzocrown ether)s 2a,bX=P(NMeN=CH-B15C5)₃ (X = O, S) and tri[bis(benzocrown ether)][N=P(NMeN=CH-B15C5)₂]₃ 3 was investigated by ¹³ C NMR spectroscopy. Using the program RMNSTAB, the complexation constants for the different possible complexes (M₂L, ML andML₂ were L represents one benzo-15-crown-5) were obtained and were compared with those of the corresponding monomer material. A remarkable ``biscrown effect' for compounds 2a,b and 3 was found, especially for potassium and rubidium by the predominant formation of stable ML₂ complexes. The strong chelate effect make these ligands highly efficient extracting agents for alkali metal picrate salts of K⁺, Rb⁺ and Cs⁺,as shown by UV-Vis spectroscopy.     

Numerical prediction of turbulent boundary layer noise from a sharp-edged flat plate

An efficient hybrid uncorrelated wall plane waves–boundary element method (UWPW-BEM) technique is proposed to predict the flow-induced noise from a structure in low Mach number turbulent flow. Reynolds-averaged Navier-Stokes equations are used to estimate the turbulent boundary layer parameters such as convective velocity, boundary layer thickness, and wall shear stress over the surface of the structure. The spectrum of the wall pressure fluctuations is evaluated from the turbulent boundary layer parameters and by using semi-empirical models from literature. The wall pressure field underneath the turbulent boundary layer is synthesized by realizations of uncorrelated wall plane waves (UWPW). An acoustic BEM solver is then employed to compute the acoustic pressure scattered by the structure from the synthesized wall pressure field. Finally, the acoustic response of the structure in turbulent flow is obtained as an ensemble average of the acoustic pressures due to all realizations of uncorrelated plane waves. To demonstrate the hybrid UWPW-BEM approach, the self-noise generated by a flat plate in turbulent flow with Reynolds number based on chord Re_c = 4.9 × 10⁵ is predicted. The results are compared with those obtained from a large eddy simulation (LES)-BEM technique as well as with experimental data from literature.     

Reactivity of Primary Phosphines and Primary Phosphine Sulfides towards Imines

Reactivity of primary phosphines with two stoichiometric equivalents of imine results in the formation of bis-α-aminophosphines ( 2 a – e ), which can be subsequently oxidized in the presence of S₈ or H₂O₂ to generate air stable bis-α-aminophosphine sulfides ( 2 b – m(S/O) ). To elucidate the mechanism of this three-component reaction, Hammett analysis, kinetic isotope effect (KIE), and trapping experiments were performed. Ultimately a P(V)–P(III) tautomerization is invoked, followed by nucleophilic attack by the P(III) species to generate the desired products.     

Bis-β-(diketonates) Zn(II) complexes substituted with thiophene: Electropolymerization,homogeneous and heterogeneous catalysis for ring opening polymerization of lactide

Two Bis-β-diketonate zinc (II) complexes were synthesized using 1-(thiophen-2-yl)butane-1,3-dione and 1-(thiophen-2-yl)-3-(thiophen-3-yl)propane-1,3-dione as ligands. By electropolymerization of their thiophenyl groups, the metallopolymers deposited on FTO electrodes were obtained. The main objective was to study the reactivity of these compounds as ROP catalysts for PLA synthesis, using directly the zinc complexes (homogeneous catalysis) and also the modified electrodes with metallopolymers (heterogeneous catalysis). The homogeneous catalysis studies allowed the optimization of the polymerization conditions, such as reaction time, catalyst concentration, and the use of benzyl alcohol as cocatalyst, as well as their influence on the conversion rate, average molecular weight and polydispersity of PLA, using rac-LA and L-LA as monomers. Also, the effect on tacticity and thermal properties were discussed. Finally, the ROP studies using immersed modified electrodes in the polymerization medium were carried out under optimized experimental conditions. These tests were positive for one of the studied compounds, reaching conversions of up to 67%. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 557–567     

Persistent Homology to Quantify the Quality of Surface-Supported Covalent Networks

Covalent networks formed by on-surface synthesis usually suffer from the presence of a large number of defects. We report on a methodology to characterize such two-dimensional networks from their experimental images obtained by scanning probe microscopy. The computation is based on a persistent homology approach and provides a quantitative score indicative of the network homogeneity. We compare our scoring method with results previously obtained using minimal spanning tree analyses and we apply it to some molecular systems appearing in the existing literature.     

Magic-angle-spinning-induced local ordering in polymer electrolytes and its effects on solid-state diffusion and relaxation NMR measurements

Magic-angle-spinning (MAS) enhances sensitivity and resolution in solid-state nuclear magnetic resonance (NMR) measurements. MAS is obtained by aerodynamic levitation and drive of a rotor, which results in large centrifugal forces that may affect the physical state of soft materials, such as polymers, and subsequent solid-state NMR measurements. Here, we investigate the effects of MAS on the solid-state NMR measurements of a polymer electrolyte for lithium-ion battery applications, poly(ethylene oxide) (PEO) doped with the lithium salt LiTFSI. We show that MAS induces local chain ordering, which manifests itself as characteristic lineshapes with doublet-like splittings in subsequent solid-state ¹ H, ⁷ Li, and ¹⁹ F static NMR spectra characterizing the PEO chains and solvated ions. MAS results in distributions of stresses and hence local chain orientations within the rotor, yielding distributions in the local magnetic susceptibility tensor that give rise to the observed NMR anisotropy and lineshapes. The effects of MAS were investigated on solid-state ⁷ Li and ¹⁹ F pulsed-field-gradient (PFG) diffusion and ⁷Li longitudinal relaxation NMR measurements. Activation energies for ion diffusion were affected modestly by MAS. ⁷Li longitudinal relaxation rates, which are sensitive to lithium-ion dynamics in the nanosecond regime, were essentially unchanged by MAS. We recommend that NMR researchers studying soft polymeric materials use only the spin rates necessary to achieve the desired enhancements in sensitivity and resolution, as well as acquire static NMR spectra after MAS experiments to reveal any signs of stress-induced local ordering.     

A Phosphoramidite Analogue of Cyclotriphosphate Enables Iterative Polyphosphorylations

An iterative polyphosphorylation approach is described, which is based on a phosphoramidite (P‐amidite) derived reagent (c‐PyPA) obtained from the cyclization of pyrophosphate with a reactive diisopropylaminodichlorophosphine. This type of reagent is unprecedented as it represents a reactive P‐amidite without protecting groups. The reagent proved to be stable in solution over several weeks. Its utility is described in the context of iterative monodirectional and bidirectional polyphosphorylations. The ensuing functionalized cyclotriphosphate can be opened with a variety of nucleophiles providing ready access to diverse functionalized polyphosphate chains of defined length with several tags, including both P‐N and P‐O labels. Their interaction with exo‐ and endopolyphosphatases is described.     

Sensitive fluorescent chemosensor for Hg(II) in aqueous solution using 4’-dimethylaminochalcone

Journal of Fluorescence - Mercury (Hg) is an element with high toxicity, especially to the nervous system, and fluorescent pigments are used to visualize dynamic processes in living cells. A little...