Effect of morphology and hydrophobization of MoS2 microparticles on the stability of poly-α-olefins lubricants

International audienceThe use of MoS ⁠ 2 nanoparticles as additive to lubricating oils is restricted by their low stability in oily media, which limits their use despite the enormous benefits associated with their intrinsic properties in terms of reduction of friction and wear coefficients. In this context, we investigated the effect of morphologies (platelets vs spheres) and surface functionalization of nanoparticles on the stability of their suspensions in poly-α-olefins (PAO) with various viscosities, which are base oils used in wind turbines. The particles were characterized by XRD, FTIR, scanning electron microscopy, atomic force microscopy and dynamic light scattering, and the stability of the resultant formulations was followed by optical (non-contact) measurements. It was found that the dispersions had similar stability despite the larger size of platelet-like particles compared to spherical ones (1-5 μm vs 600-800 nm). The dispersibility could be increased through grafting of alkylsilane on the surface defects (the longer the alkyl chain, the more stable the formulation) and with the increase of the oil kinematic viscosity (from 34 to 1705 cps at 25 °C)

Hollow carbon spheres in microwaves: Bio inspired absorbing coating

This is the final version of the article. Available from American Institute of Physics (AIP)] via the DOI in this record.The electromagnetic response of a heterostructure based on a monolayer of hollow glassy carbon spheres packed in 2D was experimentally surveyed with respect to its response to microwaves, namely, the Ka-band (26-37 GHz) frequency range. Such an ordered monolayer of spheres mimics the well-known "moth-eye"-like coating structures, which are widely used for designing anti-reflective surfaces, and was modelled with the long-wave approximation. Based on the experimental and modelling results, we demonstrate that carbon hollow spheres may be used for building an extremely lightweight, almost perfectly absorbing, coating for Ka-band applications.This work was supported in part by FP7-PEOPLE-2013- IRSES-610875 NAmiceMC, FP7 Twinning Grant Inconet EaP_004

Effect of meso vs macro-size of hierarchical porous silica on the adsorption and activity of immobilized beta-galactosidase

beta-Galactosidase (beta-Gal) is one of the most important enzymes used in milk processing for improving their nutritional quality and digestibility. Herein, beta-Gal has been entrapped into a meso-macroporous material (average pore size 9 and 200 nm, respectively) prepared by a sol&-gel method from a silica precursor and a dispersion of solid lipid nanoparticles in a micelle phase. The physisorption of the enzyme depends on the concentration of the feed solution and on the pore size of the support. The enzyme is preferentially adsorbed either in mesopores or in macropores, depending on its initial concentration. Moreover, this selective adsorption, arising from the oligomeric complexation of the enzyme (monomer/dimer/tetramer), has an effect on the catalytic activity of the material. Indeed, the enzyme encapsulated in macropores is more active than the enzyme immobilized in mesopores. Designed materials containing &;946#-Gal are of particular interest for food applications and potentially extended to bioconversion, bioremediation, or biosensing when coupling the designed support with other enzymes.7º Programa Marco de la UE FP7/2007-2013/, Programa People

Fully carbon metasurface: Absorbing coating in microwaves

This is the author accepted manuscript. The final version is available from AIP Publishing via the DOI in this record.The microwave-absorbing properties of a heterostructure consisting of an ordered monolayer of porous glassy carbon spheres were experimentally and theoretically investigated in the Ka-band (26–37 GHz) frequency range. The electromagnetic response of such a “moth-eye”-like all-carbon metasurface at a normal incidence angle was modelled on the basis of long-wave approximation. Modelling parameters in the Ka-band were used to estimate and predict the absorption properties of monolayers in free space in the range 1–40 GHz. Experimental and theoretical results demonstrate that a metasurface based on porous glassy carbon spheres is an inert, lightweight, compact, and perfectly absorbing material for designing new effective microwave absorbers in various practically used frequency ranges.The work was supported by Projects FP7-610875 (NAMICEMC, 2013-2017), H2020 RISE 734164 Graphene 3D, and FP7 IRSES project CANTOR (Grant No. FP7-612285). Sijin Li thanks the China Scholarship Council for the financial support under Grant No. 201406510029. Cameron Gallagher and Emma Burgess acknowledge financial support from the Engineering and Physical Sciences Research Council (EPSRC) of the United Kingdom, via the EPSRC Centre for Doctoral Training in Metamaterials (Grant No. EP/L015331/1)

Differences between beta-Ala and Gly-Gly in the design of amino acids-based hydrogels

Despite the continuous interest in organogels and hydrogels of low molecular weight gelators (LMWG), establishing the relationship between the molecular structure and the gelation mechanism is still a challenge. In this paper our interest focuses on the consequences of slight molecular modifications on the self-assembling behaviour of β-Ala vs Gly-Gly-based hydrogelators. Previously, in our group, amino acid based amphiphiles i.e. Gly-Gly-His-EO₂-Alk, a trimodular amphiphile (containing three domains: H-bond donor and acceptor/hydrophilic/hydrophobic domain, respectively) were reported to act as hydrogelators and that the gelation properties were related to hydrogen bonding, hydrophobic interactions and π-π stacking. Herein, β-Ala-His-EO₂-Alk was fully characterised by FT-IR, NMR, SAXS and SEM and the gelation mechanism is discussed. It appears that the number of amide groups determines the self-assembling behaviour into 1D or 2D/3D networks as a result of intimate interactions between gelator molecules

Constitutional self-organization of adenine-uracil-derived hybrid materials

International audienceThe alkoxysilane nucleobase adenine (A) and uracil (U) precursors described in this paper generate in solution a complex library of hydrogenbonded aggregates, which can be expressed in the solid state as discrete higher oligomers. The different interconverting outputs that nucleobases may form by oligomerization define a dynamic polyfunctional diversity that may be "extracted selectively" in solid state by sol-gel transcription, under the intrinsic stability of the system. After he sol-gel process, unique constitutional preference for specific geometries in hybrid materials is consistent with a preferential arrangement of nucleobase systems, favoring the self-assembly by the Hoogsteen geometry. FTIR and NMR spectroscopy and -ray powder diffraction experiments demonstrate the formation of self-organized hybrid supramolecular materials. Electron microscopy reveals the micrometric platelike morphology of the hybrid materials. The MA-U hybrid material is nanostructured in ordered circular domains of 5 nm in diameter of alternative light and dark rows with an one-dimensional periodicity of 3.5 A°