GaN nanowires for piezoelectric generators

We demonstrate the high potential of GaN nanowires (NWs) to convert mechanical energy into electric energy. Using an atomic force microscope equipped with a Resiscope module, an average output voltage of –74 mV and a maximum of –443 mV ± 2% per NW were measured. This latter value is the highest reported so far for GaN NWs. By considering these output signals, we have estimated an average and a maximum power density generated by one layer of GaN NWs of the order of 5.9 mW/cm² and 130 mW/cm², respectively. These results offer promising prospects for the use of GaN NWs for high‐efficiency ultracompact piezogenerators. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

An algorithm for the separation of two-row cuts

We consider the question of finding deep cuts from a model with two rows of the type $P_I=\{(x,s)\in \mathbb{Z }^2\times \mathbb{R }^n_+ : x=f+Rs\}$ . To do that, we show how to reduce the complexity of setting up the polar of $\mathop {\mathrm{conv}}(P_I)$ from a quadratic number of integer hull computations to a linear number of integer hull computations. Furthermore, we present an algorithm that avoids computing all integer hulls. A polynomial running time is not guaranteed but computational results show that the algorithm runs quickly in practice.     

Skin Constituents as Cosmetic Ingredients. Part I: A Study of Bio‐mimetic Monoglycerides Behavior at the Squalene‐Water Interface by the “Pendant Drop” Method in a Static Mode

This work presents the behavior of bio‐mimetic monoglycerides at the squalene/water interface. The study was done in the so‐called “static” mode using the “pendant drop method”, enabling us to characterize these molecules according to the value of their critical efficiency concentration (CEC), their maximum surface excess concentration (Γ_∞), the efficiency of the surface tension reduction parameter (pC20), and the minimum value of their interfacial tension (γ_min). It also permitted the study of the influence of the structure of the carbon chain of those monoglycerides on their interfacial behavior.

The analysis of the different parameters shows that monoglycerides with small hydrocarbon chains, monoglycerides with one or more double bonds, and monoglycerides possessing a hydroxyl function grafted in the middle of the chain constitute excellent surfactants. Two different groups can be found: one group composed of short saturated hydrocarbon chain monoglycerides (C12∶0 to C16∶0) and long hydrocarbon chain monoglycerides (C18∶0 to C22∶0); the second group, composed of unsaturated hydrocarbon chain monoglycerides, also includes hydroxystearate and isostearate monoglycerides. The first group could be used for the formulation of “hydrating” cosmetic products having secondary droplets, the second group for W/O emulsions.     

Concise synthesis of di- and trisaccharides related to the O-antigens from Shigella flexneri serotypes 6 and 6a,based on late stage mono-O-acetylation and/or site-selective oxidation

Shigella flexneri serotypes 6 and 6a are closely related bacteria causing shigellosis in humans. Their O-antigens are {→4)-β-d-GalpA-(1→3)-β-d-GalpNAc-(1→2)-[3Ac/4Ac]-α-l-Rhap-(1→2)-α-l-Rhap-(1→}_n acidic polysaccharides ({AB_AcCD}_n), which only differ in the degree of O-acetylation. A concise synthesis of two disaccharides (BC, B_AcC) and four trisaccharides, representing portions and/or analogs of the O-antigens, is described. A protected intermediate compatible with late stage 3_C-O-acetylation, and/or galactosyl (A°) to galacturonic acid (A) conversion, was designed and assembled from trichloroacetimidate and thioglycoside donors tuned for high yielding glycosylation and excellent stereocontrol. The galacturonic moiety was efficiently introduced from galactose using a TEMPO/NaOCl/NaClO₂-based oxidation protocol optimized for full compatibility with sensitive moieties, such as allyl ethers and acetates. Final Pd/C-mediated deprotection provided the targets, including the propyl glycoside AB_AcC, its non O-acetylated counterpart ABC, and the non acidic analogs A°B_AcC and A°BC. The BC and ABC oligosaccharides are also portions of the O-antigen from Escherichia coli O147, which causes diarrhea in pigs.     

Janus carbosilane/phosphorhydrazone dendrimers synthesized by the ‘click’ Staudinger reaction

The first association of carbosilane dendrons (having a phosphine at the focal point) with phosphorhydrazone dendrons (having a thiophosphoryl azide at the focal point) has been successfully carried out by ‘Staudinger click’ reaction. The corresponding Janus dendrimers possess the characteristics of both components; they are oily as the carbosilane dendrons, and they can be easily functionalized as the phosphorhydrazone dendrons.     

Biodegradation study of plasticised corn flour/poly(butylene succinate-co-butylene adipate) blends

Plasticised corn flour/poly(butylene succinate-co-butylene adipate) (PBSA) materials were prepared by extrusion and injection in order to study the impact of PBSA ratio on their physicochemical properties and biodegradability. Scanning electron microscopy observations showed that corn flour and PBSA are incompatible. Three types of morphology have been observed: (i) starch dispersed in a PBSA matrix, (ii) a “co-continuous-like” morphology of starch and PBSA, and (iii) PBSA dispersed in a starch matrix. As expected, the extent of plasticised corn flour starch hydrolysis by amylolytic enzymes decreased when the amount of PBSA increased. Addition of a lipase to hydrolyse PBSA ester bonds enhanced enzymatic hydrolysis of starch by amylolytic enzymes in materials where PBSA formed a continuous phase. This suggests that PBSA formed a barrier restricting the access of amylolytic enzymes to starch. This was consistent with aerobic and anaerobic biodegradation assays, which also showed lower biodegradability of materials containing a majority of PBSA.     

Heteroleptic Tin(II) Initiators for the Ring‐Opening (Co)Polymerization of Lactide and Trimethylene Carbonate: Mechanistic Insights from Experiments and Computations

The tin(II) complexes {LO^x}Sn(X) ({LO^x}^?=aminophenolate ancillary) containing amido ( 1 – 4 ), chloro ( 5 ), or lactyl ( 6 ) coligands (X) promote the ring‐opening polymerization (ROP) of cyclic esters. Complex 6 , which models the first insertion of L ‐lactide, initiates the living ROP of L ‐LA on its own, but the amido derivatives 1 – 4 require the addition of alcohol to do so. Upon addition of one to ten equivalents of iPrOH, precatalysts 1 – 4 promote the ROP of trimethylene carbonate (TMC); yet, hardly any activity is observed if tert‐butyl (R)‐lactate is used instead of iPrOH. Strong inhibition of the reactivity of TMC is also detected for the simultaneous copolymerization of L ‐LA and TMC, or for the block copolymerization of TMC after that of L ‐LA. Experimental and computational data for the {LO^x}Sn(OR) complexes (OR=lactyl or lactidyl) replicating the active species during the tin(II)‐mediated ROP of L ‐LA demonstrate that the formation of a five‐membered chelate is largely favored over that of an eight‐membered one, and that it constitutes the resting state of the catalyst during this (co)polymerization. Comprehensive DFT calculations show that, out of the four possible monomer insertion sequences during simultaneous copolymerization of L ‐LA and TMC: 1) TMC then TMC, 2) TMC then L ‐LA, 3) L ‐LA then L ‐LA, and 4) L ‐LA then TMC, the first three are possible. By contrast, insertion of L ‐LA followed by that of TMC (i.e., insertion sequence 4) is endothermic by +1.1 kcal mol^?1, which compares unfavorably with consecutive insertions of two L ‐LA units (i.e., insertion sequence 3) (?10.2 kcal mol^?1). The copolymerization of L ‐LA and TMC thus proceeds under thermodynamic control.     

Chain-extending of Hydroxytelechelic Polybutadiene: Synthesis and Characterization

Extension of hydroxytelechelic polybutadiene oligomers ( 3200 g/mol) is performed in mild conditions, in order to avoid backbone modifications, using succinic anhydride or methylenedicyclohexyl diisocyanate. The two routes present significative extension of the initial oligomers. Extension through the anhydride route, in the presence of DCC and DMAP, leads to new hydroxytelechelic oligomers ( 8000 g/mol). Extension through the diisocyanate route, catalyzed by DBTL at 65°C leads to hydroxytelechelic oligomers of higher average molecular weight ( 20000 g/mol). New materials are characterized by FTIR/¹H-NMR and changes in their Tg according to , are discussed. The influence of reaction time on the length of the macromolecular chains is also studied.