Nature of the Metal Insulator Transition in High-Mobility 2D_Si-MOSFETs.

Our investigation focuses on the analysis of the conductive properties of high-mobility 2D-Si-MOSFETs as they approach the critical carrier density, nsc (approximately 0.72×1011 cm-2), which marks the metal insulator transition (MIT). In close proximity to the nsc, the conductivity exhibits a linear dependence on the temperature ().

NMR investigation on the thermogelation of partially hydrolysed polyacrylamide/polyethylenimine mixtures.

Since the introduction of polyethylenimine (PEI)/acrylamide-based polymer gel systems in the late 90's, the literature knowledge on the crosslinking mechanisms between the various polymers (PAM, PHPA, and PatBA) and the crosslinker (PEI) was only limited to observations on gelation times and gel strength variations compared to other gel systems. In this paper, classic proton and carbon nuclear magnetic resonance "NMR" experiments and advanced 2D DOSY and NOESY techniques were employed for studying the interactions between the amine groups of PEI and amide or carboxylate groups of partially hydrolysed polyacrylamide (PHPA). Among the many possibilities, we showed that the interaction occurring during thermogelation is mainly due to covalent bonding.

Biosourced Polymeric Emulsifiers for Miniemulsion Copolymerization of Myrcene and Styrene: Toward Biobased Waterborne Latex as Pickering Emulsion Stabilizer.

Biobased waterborne latexes were synthesized by miniemulsion radical copolymerization of a biosourced β-myrcene (My) terpenic monomer and styrene (S). Biobased amphiphilic copolymers were designed to act as stabilizers of the initial monomer droplets and the polymer colloids dispersed in the water phase. Two types of hydrophilic polymer backbones were hydrophobically modified by terpene molecules to synthesize two series of amphiphilic copolymers with various degrees of substitution.

Hemisynthesis of coumarin derivatives from oil extract: organobase-catalyzed reaction, analytical study by diffusion-ordered spectroscopy NMR and differential scanning calorimetry.

This paper presents an in-depth chemical and analytical study of a natural substance extracted from Coss. & Dur and its derivatives after hemisynthesis. The analysis was performed using Diffusion-Ordered Spectroscopy (NMR DOSY) and Differential Scanning Calorimetry (DSC) as general methods.

Novel Hydroquinone-Alumina Composites Stabilizing a Guest-Free Clathrate Structure: Applications in Gas Processing.

Organic clathrates formed by hydroquinone (HQ) and gases such as CO and CH are solid supramolecular host-guest compounds in which the gaseous guest molecules are encaged in a host framework of HQ molecules. Not only are these inclusion compounds fascinating scientific curiosities but they can also be used in practical applications such as gas separation. However, the development and future use of clathrate-based processes will largely depend on the effectiveness of the reactive materials used.

Phosphorus pentoxide as a cost-effective, metal-free catalyst for ring opening polymerization of ε-caprolactone.

The ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) using phosphorus pentoxide (PO) as a metal-free catalyst and isopropanol (iPrOH) as initiator resulted in the preparation of poly(ε-caprolactone) with narrow weight distribution. NMR spectroscopy analyses of the prepared PCL indicated the presence of the initiator residue at the end of the polymer chain, implying the occurrence of the ε-CL-catalysis ROP through a monomer activation mechanism. Kinetic experiments confirmed the controlled/living nature of ε-CL ring-opening catalyzed by phosphorus pentoxide.

Formulation of Multifunctional Materials Based on the Reaction of Glyoxalated Lignins and a Nanoclay/Nanosilicate.

Two organosolv lignins from different origins, namely, almond shells and maritime pine, were modified by using a nanoclay and nanosilicate. Prior to modification, they were activated via glyoxalation to enhance the reactivity of the lignins and thus ease the introduction of the nanoparticles into their structure. The lignins were characterized by several techniques (Fourier transformed infrared, high-performance size exclusion chromatography, H NMR, X-ray diffraction, and thermogravimetric analysis) before and after modification to elucidate the main chemical and structural changes.

Interactions between quaternized chitosan and surfactant studied by diffusion NMR and conductivity.

Surfactant-polysaccharide complexes (SPEC) based on oppositely charged sodium 1-decanesulfonate and quaternized chitosan were studied using two techniques. The first one, the conductivity, is a very often used even when diffusion NMR (DOSY) technique was considered for the first time for such systems involving surfactant and chitosan derivatives and more generally polysaccharides. The physico-chemical characteristics of pure surfactant solutions as well as SPECs were determined and compared according to the considered experimental technique.

Chitosan-graft-polyaniline-based hydrogels: elaboration and properties.

Intrinsically conducting polymers are of great interest for a large number of applications. But among the major drawbacks are their low solubility in common solvents and their poor mechanical properties. Elaboration of composites associating a matrix, bringing its mechanical properties, and polyaniline, as the conducting polymer, is a way of overcoming these disadvantages.

Kinetic aspects, rheological properties and mechanoelectrical effects of hydrogels composed of polyacrylamide and polystyrene nanoparticles.

Snake-cage gels were prepared using monodisperse polystyrene (PS) nano-sized particles ( = 200 nm) in place of the more commonly used linear polymer. The kinetics of the formation of the complementary polyacrylamide (PAM) hydrogel was studied alone or in the presence of the PS nanoparticles by H-NMR. Without PS, the reactivity ratios of the acrylamide (Am) and the cross-linking agent ,'-methylene-bisacrylamide (BisAm) were computed using the initial kinetics of PAM gel at high cross-linker concentration ( = 0.

Study of sodium dodecyl sulfate-poly(propylene oxide) methacrylate mixed micelles.

Sodium dodecyl sulfate (SDS)-poly(propylene oxide) methacrylate (PPOMA) (of molecular weight M(w) = 434 g x mol(-1)) mixtures have been studied using conductimetry, static light scattering, fluorescence spectroscopy, and 1H NMR. It has been shown that SDS and PPOMA form mixed micelles, and SDS and PPOMA aggregation numbers, N(ag SDS) and N(ag PPOMA), have been determined. Total aggregation numbers of the micelles (N(ag SDS) + N(ag PPOMA)) and those of SDS decrease upon increasing the weight ratio R = PPOMA/SDS.

Oxidation of sulfides and disulfides under electron transfer or singlet oxygen photosensitization using soluble or grafted sensitizers.

Two different photosensitizers, 9,10-dicyanoanthracene (DCA) and benzophenone (BzO) or a silica bound derivative (BzO-Si) have been compared for the photooxidation of di-n-butyl sulfide and di-n-butyl disulfide. With either photosensitizer, sulfide photooxidation in acetonitrile leads very efficiently to sulfoxide, with sulfone and disulfides as by-products. Although an electron transfer mechanism has previously been established starting with DCA, our results are indicative of two competitive mechanisms using BzO as the photosensitizer, instead of singlet oxygen addition and electron transfer.