Rénal Backov

Combining soft matter and soft chemistry: integrative chemistry towards designing novel and complex multiscale architectures

There is today a strong and emerging commitment toward designing complex and hierarchical architectures. In this context, great interest is appearing in the combination of soft chemistry and complex fluids. In any circumstance we can see that there is a strong affinity between and as they can interact together without disrupting their own function. For instance, a continuous network should emerge from the former while the latter should promote patterning effects. In this general context, the new concept of is proposed as well as its principle and main perspectives.

Porous mediator-free enzyme carbonaceous electrodes obtained through Integrative Chemistry for biofuel cells

In the present study we have shown that carbonaceous micro/macrocellular foams can be used for efficient and stable non-specific enzyme entrapment. In this context, Bilirubin Oxidase adsorbed into the porous electrode is able to reduce O2 to water and electrons are transferred directly from the electrode to the enzyme without the need of a redox mediator. The reduction current is stable for several days under continuous operation and therefore we consider the carbonaceous foams are very promising candidates for the construction of 3-dimensional biofuel cell cathodes. Mediator free, the electrode preparation and further enzyme adsorption are extremely simple, low cost and versatile. Most important, the excellent mechanical strength and the synthetic route allow us to design at will the size and external shape of the electrodes, which are of vital importance if we wish to incorporate electrodes into devices. The Integrative Chemistry synthetic route allows accessing hierarchical porosities with the advantage of specific functionalities. Macropores serve to fuel transport and micropores as anchoring sites for enzyme entrapment. Despite the inability to reach the Levich diffusion limited current suggesting that the porosity is not yet fully optimized, the results presented here show that porous carbonaceous foam electrodes allow for an incredible increase in enzyme loading which allows for a 500-fold current enhancement and stabilization of the direct electron transfer current from few hours to several days as compared to conventional flat electrodes.

Magnetic Spin Ladder (C5H12N)2CuBr4: High Field Magnetization and Scaling Near Quantum Criticality

The magnetization, M(H< or =30 T,0.7< or =T< or =300 K), of (C5H12N)2CuBr4 has been used to identify this system as an S = 1/2 Heisenberg two-leg ladder in the strong-coupling limit, J( perpendicular) = 13.3 K and J( parallel) = 3.8 K, with H(c1) = 6.6 T and H(c2) = 14.6 T. An inflection point in M(H,T = 0.7 K) at half saturation, M(s)/2, is described by an effective XXZ chain. The data exhibit universal scaling behavior in the vicinity of H(c1) and H(c2), indicating that the system is near a quantum critical point.

Preparation of LiBH4@carbon micro–macrocellular foams: tuning hydrogen release through varying microporosity

Microporous–macroporous carbononaceous monolith-type materials, prepared through a hard template method using silica as exo-templating matrices, have been impregnated with an etheric solution of LiBH4 to prepare LiBH4@carbon samples. It has been shown that the amorphous character of LiBH4 is largely favoured when developing the carbon microporosity (pores smaller than 2 nm) and that, as a consequence, the LiBH4 dehydrogenation is strongly enhanced at low temperatures. The onset temperature of dehydrogenation can be decreased to 200 °C and hydrogen capacity reaching 4.0 wt% is obtained at 300 °C with the carbon having the largest microporous volume, whereas the hydrogen release for bulk LiBH4 is negligible at the same temperature. It is suggested both from DSC and from pressure values reached upon hydrogen release that the enthalpy of the dehydrogenation reaction is strongly modified. In addition to some irreversible reactions with carbon surface groups (and even with the carbon matrix itself according to 11B MAS NMR spectroscopy, which reveals the formation of B–C bonds), the explanation for such modification could lie in the LiBH4 destabilization through confinement to the nanoscale range and associated amorphization. The above feature, where LiBH4 crystalline character is tuned through the imposed microporosity, can be considered as a highly promising approach to control the hydrogen release temperature of complex hydrides.

Foam Drainage in the Presence of Nanoparticle−Surfactant Mixtures

The drainage of SiO(2) nanoparticle-cationic surfactant (TTAB) mixtures through calibrated aqueous foams had been studied by combining several approaches on both the macroscopic and the local scale. Macroscopic measurements reveal a strong stabilizing effect arising for nanoparticle concentrations as low as 2 wt % mainly because of a drainage kinetic slow-down dependent on the nanoparticle concentration. We show that the variation of the viscous parameters (bulk viscosity, interfacial viscosity, or both) in the classical theoretical models of foam drainage, mainly developed for aqueous surfactant solutions, does not enable fitting experimental data obtained via steady- or free-drainage strategies for [SiO(2)] > or = 2 wt %. In contrast, the quantitative analysis of the data obtained from front propagation velocities has revealed a drainage regime transition from a node-dominated regime toward a Plateau-border-dominated regime upon nanoparticle concentration increase. Observations performed at the Plateau border scale brought to light the drainage kinetic slow-down process by evidencing that the presence of insoluble aggregates induces traffic jamming and even cork formation for silica concentrations above 2 wt %. Considering these observations, a simple mechanism of aggregate growth and cork formation is proposed. Finally, we analyze the discrepancy between experiments (steady- and free-drainage methods) and theory by pointing out that the hypothesis relative to the foam structure that is usually assumed for both the liquid fraction calculation and the determination via conductivity measurements is strongly modified when large insoluble aggregates are present in the system. In this view, the method based on the liquid fraction determination through the measurement of the front propagation velocity seems to be the most suitable for studying the drainage of colloidal dispersion because of the lower dependence of this approach toward hypothesis on the local geometry of the foam continuous phase.

Bio-inspired synthetic pathways and beyond: integrative chemistry

Herein are described some rational synthetic pathways for generating complex architectures with enhanced application in either optics, catalysis, phase separation or magnetism. The ability of integrative chemistry to scissor condensed matter at several length scales where final objects will be macroscopically one-dimensional (1D), two-dimensional (2D) or three-dimensional (3D) is discussed. In this general context, the first section deals with fibers generated either through electrospinning or extrusion processes bearing, respectively, magnetic and sensor properties. The second part is dedicated to periodic mesostructured thin films (POMTFs) and nanotextured films obtained, respectively viaEISA and Langmuir–Blodgett techniques, where optical properties will be an issue in both cases through respectively sensing and photo band gap properties. Finally the third part will dedicated to pseudo 3D objects, namely membranes, and 3D mesomacrocellular foams, promoted respectively by mesoscale-driven self organization and emulsion-based synthetic routes where final applications will range from filtration to heterogeneous catalysis. After briefly discussing some challenges that should be addressed in the future for “integrative chemistry”, we conclude that it should be seen as an “interdisciplinary tool box”, being a specific space of freedom where each chemist can express his or her own creativity through a rational approach.

Novel monolith-type boron nitride hierarchical foams obtained through integrative chemistry

A novel class of monolith-type boron nitride hierarchical foams has been prepared through an integrative chemistry-based synthetic path. These materials contain interconnected pores in the nanometre to the micrometre range with high porosity (∼75 vol%), a specific surface area up to 300 m2 g−1 and a resistance toward mechanical stress making them suitable for innovative applications.

Syntheses and characterization of highly mesoporous crystalline TiO2 macrocellular foams

Titanium dioxide open-cell macro-cellular foams have been generated with emphasis toward controlling macro-, meso- and microstructures thus reaching hierarchically organized inorganic architectures. At the macroscopic length scale a non-static air–liquid foam strategy allows strong control over the open-cell morphologies. At the meso- and/or nanoscopic length scales various mesogenic templates or latex colloids have been used to promote mesoporosity. Among the strategies in use, a Pluronic copolymer P-123 combined with tetradecyltrimethylammonium bromide induce vermicular-like mesoporosity associated with a specific surface area around 400 m2 g−1. At the microscopic length scale, upon the use of specific thermal treatment, either monophasic anatase, biphasic anatase–rutile or monophasic rutile allotropic forms are obtained.

Thermostimulable Wax@SiO2 Core-Shell Particles

We propose a new synthesis pathway without any sacrificial template to prepare original monodisperse thermoresponsive capsules made of a wax core surrounded by a silica shell. Under heating, the inner wax expands and the shell breaks, leading to the liquid oil release. Such capsules that allow triggered deliverance provoked by an external stimulus belong to the class of smart materials. The process is based on the elaboration of size-controlled emulsions stabilized by particles (Pickering emulsions) exploiting the limited coalescence phenomenon. Then the emulsions are cooled down and the obtained suspensions are mineralized by the hydrolysis and condensation of a monomer at the wax-water interface, leading to the formation of capsules. The shell break and the liquid oil release are provoked by heating above the wax melting temperature. We characterize the obtained materials and examine the effect of processing parameters and heating history. By an appropriate choice of the wax, the temperature of release can easily be tuned.

Growth of calcium oxalate monohydrate at phospholipid Langmuir monolayers

Abstract Calcium oxalate monohydrate crystals have been nucleated from metastable solutions at Langmuir monolayers of the phospholipids dipalmitoylphosphatidylglycerol (DPPG), dipalmitoylphosphatidylserine and dipalmitoylphosphatidylcholine and the fatty acid arachidic acid. The phospholipid monolayers were used as model systems for domains of pure lipid in cellular media as part of investigations of their potential role in the nucleation of calcium oxalate in the urinary tract. Crystal formation was monitored at the air/water interface using Brewster angle microscopy and in transferred films using SEM and TEM. For each Langmuir monolayer, it was observed that nucleation is heterogeneous and is selective with respect to the orientation and morphology of the precipitated crystals with up to 90% of crystals growing with the ( 1 0 1 ) face oriented towards the monolayer interface. The selectivity is attributed to calcium binding at the lipid monolayer favoring formation of the calcium-rich ( 1 0 1 ) face. The behavior at each monolayer was similar, although a higher rate of crystal formation was observed at the anionic DPPG interface.