Synthesis and physicochemical characterization of a novel ampholytic pullulan derivative with amphiphilic behavior in alkaline media

International audiencePullulan derivative was synthesized by coupling carboxymethylpullulan (degree of substitution ) and dimethylaminopropylamine (DMAPA), activated by a hydrosoluble carbodiimide -(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride (EDAC). FTIR and 13C and 1H NMR spectroscopic analyses have evidenced that the polysaccharide has been successfully modified. 1H NMR, nitrogen analysis, and conductimetric measurements allow determination of the degree of substitution in both carboxylic acid and amine functions. We have found that both functions present a similar DS of 0.35, which is characteristic of an ampholytic polymer with possible zwitterionic-type properties. Solution properties have been studied by flow field flow fractionation (F4) coupled on-line with multiangle laser light scattering (MALLS) and quasi elastic light scattering (QELS), surface tension, and viscosity measurements. The behavior has been found largely pH dependent and an amphiphilic behavior has been evidenced in alkaline media

Study and optimization of a 600V Pseudo-vertical GaN-on-silicon rectifier by finite elements simulation

International audienceReal performance breakthrough have been demonstrated for high voltage, high power, high temperature and high frequency devices by using wide band-gap semiconductors, such as 4H-SiC, GaN and AlGaN, over the previously existing devices based on group-IV and III-V lower band-gap semiconductor material. One of the key devices for high power switching converter is a fast rectifier. 4H-SiC based Schottky diodes are now commercially available from many companies with breakdown voltage up to 1,7 kV. However, bulk SiC substrates are very expensive and the hetero-epitaxial SiC layers on low cost substrates have too many crystal defects. These are the main reasons for the ongoing research programs toward GaN based-rectifiers on Silicon substrate for medium voltage range applications (600 V < Vbr < 1.2 kV)

Novel cationic and amphiphilic pullulan derivatives II: pH dependant physicochemical properties

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Study and optimization of a 600V Pseudo-vertical GaN-on-silicon rectifier by finite elements simulation

International audienceReal performance breakthrough have been demonstrated for high voltage, high power, high temperature and high frequency devices by using wide band-gap semiconductors, such as 4H-SiC, GaN and AlGaN, over the previously existing devices based on group-IV and III-V lower band-gap semiconductor material. One of the key devices for high power switching converter is a fast rectifier. 4H-SiC based Schottky diodes are now commercially available from many companies with breakdown voltage up to 1,7 kV. However, bulk SiC substrates are very expensive and the hetero-epitaxial SiC layers on low cost substrates have too many crystal defects. These are the main reasons for the ongoing research programs toward GaN based-rectifiers on Silicon substrate for medium voltage range applications (600 V < Vbr < 1.2 kV)

Chemical and Physicochemical Investigation of an Aminoalkylalkoxysilane As Strengthening Agent for Cellulosic Materials

International audienceAMDES (aminopropylmethyldiethoxysilane) was used to investigate the physicochemical and chemical events related to the introduction of aminoalkylalkoxysilanes in cellulosic materials. Using 29Si CP-MAS and 1H NMR to study the reactivity and structural modification of AMDES in the paper it was shown that polymerization occurs in situ. The distribution of the active compound on the surface of the fibers and throughout the fibers’ thickness was visualized by SEM-EDS. A relation between moisture content, fiber swelling, and uptake of AMDES was found. To better represent old and brittle documents, the paper was predegraded by oxidation with sodium hypochlorite. XRD confirmed the advanced destruction of the amorphous areas of cellulose. Adding AMDES in the oxidized paper resulted in improved mechanical properties, a roughly unmodified degree of polymerization of cellulose, but a slight increase in the yellowing, probably due to several possible reaction products such as imines, amine, amides, and Maillard reactions products. The deacidification efficacy was established and the strengthening effect was shown to arise from the interaction of AMDES with the cellulose fibers

The impact of paper constituents on the efficiency of mechanical strengthening by polyaminoalkylalkoxysilanes

International audienceThe aim of the research was to evaluate the influence of certain components of paper such as lignin and papermaking additives (fillers and sizing) on the efficiency of a recently proposed treatment for simultaneous deacidification and mechanical strengthening with polyaminosiloxane copolymer networks. Mixed mechanical and chemical pulp papers containing various additives were treated with aminoalkylalkoxysilanes (AAAS) by immersion or by spray. Upon treatment, the deposited alkaline reserve varied from 0.34 to 1.14 mol kg−1. For all the papers, copolymers formed from binary mixtures of a di- and a tri-functional AAAS provided the best improvement in the mechanical properties, i.e. in the tensile strength and the folding endurance, indicating an increase in the interfiber bonding energy and in the paper flexibility and plasticity, respectively. It was found that fillers had no influence while sizing hampered the efficiency of the treatment. The presence of mechanical pulp was shown to have a significant impact on the effect of the treatments as well by increasing the tensile resistance more than the folding endurance, indicating an increase in the paper rigidity. This observation was attributed to the response of lignin to the treatment