Poly(dithiotriethylene adipate): Melting behavior, crystallization kinetics and morphology

The melting behavior and the crystallization kinetics of poly(dithiotriethylene adipate) (PSSTEA) were investigated by differential scanning calorimetry and hot-stage optical microscopy. The observed multiple endotherms, commonly displayed by polyesters, were influenced by the crystallization temperature (T_c) and ascribed to melting and recrystallization processes. Linear and nonlinear theoretical treatments were applied to estimate the equilibrium melting temperature for PSSTEA, using the corrected values of the melting temperature; the nonlinear estimation yielded a higher value by about 15 °C. Isothermal crystallization kinetics were analyzed according to the Avrami’s theory. Values of the Avrami’s exponent n close to 3 were obtained, independently of T_c, in agreement with a crystallization process originating from predeterminated nuclei and characterized by three-dimensional spherulitic growth. As a matter of fact, space-filling spherulites were observed by optical microscopy at all T_c’s. The rate of crystallization became lower as T_c increased, as usual at low undercooling, the crystallization process being controlled by nucleation.     

MnO x /ZrO2 gel-derived materials for hydrogen peroxide decomposition

Manganese-yttrium-zirconium mixed oxide nanocomposites with three different Mn loadings (5, 15 and 30 wt%) were prepared by sol–gel synthesis. Amorphous xerogels were obtained for each composition. Their structural evolution with the temperature and textural properties were examined by thermogravimetry/differential thermal analysis, X-ray diffraction, diffuse reflectance UV–vis spectroscopy and N₂ adsorption isotherms. Mesoporous materials with high surface area values (70–100 m² g⁻¹) were obtained by annealing in air at 550 °C. They are amorphous or contain nanocrystals of the tetragonal ZrO₂ phase (T-ZrO₂) depending on the Mn amount and exhibit Mn species with oxidation state higher than 2 as confirmed by temperature programmed reduction experiments. T-ZrO₂ is the only crystallizing phase at 700 °C while the monoclinic polymorph and Mn₃O₄ start to appear only after a prolonged annealing at 1,000 °C. The samples annealed at 550 °C were studied as catalysts for H₂O₂ decomposition in liquid phase. Their catalytic activity was higher than that of previously studied Mn/Zr oxide systems prepared by impregnation. Catalytic data were described by a rate equation of Langmuir type. The decrease of catalytic activity with time was related to dissolution of a limited fraction (up to 15%) of Mn into the H₂O₂/H₂O solution.     

Pulse energy scaling to 5 microJ from a femtosecond thin disk laser

We report an increase in pulse energy to 5.1 microJ obtained directly from a femtosecond diode-pumped Yb:YAG thin disk laser without external amplification. Stable passive mode locking was obtained with a semiconductor saturable absorber mirror (SESAM). The laser delivers 63 W of average output power in a nearly diffraction-limited beam (M2=1.1) at a center wavelength of 1030 nm. The pulse repetition rate is 12.3 MHz, and the pulses have a duration of 800 fs, which results in a peak power of 5.6 MW. The laser was operated in a box flooded with helium because the nonlinearity of air was found to be a limiting factor for the stability of the pulse formation at increasing pulse energies.     

About Durability of Biodegradable Polymers: Structure/Degradability Relationships

Up to now materials were chosen to satisfy specific property(ies) in relation with the required application. Nowadays, a specific attention has to be devoted to the durability of this property regarding to the lifetime duration. It is the reason why, we paid attention about degradability. Thus, a screening of bio- and photodegradability of various selected (co)polyesters has been achieved in order to get better insights about structure / durability relationships. We developed tools allowing the prediction of the behavior of materials upon ageing and the evolution of their properties, regarding to their initial chemical structures. Hence, we could be able to design (co)polyesters characterized by well-adapted physical, thermal and mechanical properties, but also, with high photostability and/or high biodegradability.     

Liquid chromatographic/mass spectrometric determination of desmedipham and phenmedipham and their metabolites in soil

A simple method is described for the simultaneous determination of residues of 2 carbamate herbicides (phenmedipham and desmedipham) and related metabolites (m-aminophenol, aniline, and m-toluidine) in soil. The analytes are extracted from spiked soils with methanol. The solvent/soil suspension is centrifuged, and the supernatant is directly injected, without any further cleanup, into a reversed-phase liquid chromatography/mass spectrometry apparatus equipped with a TurbolonSpray interface. The method was tested on 5 soils having different physicochemical properties. Recoveries from the soil types, spiked over the range of 50-200 ppb, were essentially quantitative for each analyte. The detection limits of the method are < or = 25 ng/g.     

Powerful red-green-blue laser source pumped with a mode-locked thin disk laser

We present a red-green-blue laser source with average powers of 8 W in the red, 23 W in the green, and 10.1 W in the blue. The entire pump power for the nonlinear conversion stages is provided by a single laser oscillator without any amplifier stages. Our system does not require any synchronized cavities, and all nonlinear crystals except one are critically phase matched at room temperature.     

Influence of Pore Size in Benzoin Condensation of Furfural Using Heterogenized Benzimidazole Organocatalysts

A designed N-heterocyclic carbene (NHC) catalyst was covalently anchored on a range of mesoporous and hierarchical supports, to study the influence of pore size in the benzoin condensation of furfural. The structural and spectroscopic characteristics of the anchored catalysts were investigated, also with the help of molecular dynamics simulations, in order to rationalize the degree of stability and recyclability of the heterogenized organocatalysts. Quantitative yields (99 %) and complete recyclability were maintained after several cycles, vindicating the design rationale.     

Effect of solvent composition on signal intensity in liquid chromatography-matrix-assisted laser desorption ionization experiments

The use of reversed phase liquid chromatography for the preparation of complex peptide mixtures for analysis by matrix assisted laser desorption ionization mass spectrometry has led to the observation of the critical importance of the matrix/analyte formulation in regards to the percent organic solvent in the mixture. This paper outlines the study using liquid chromatography to systematically vary the acetonitrile concentration in the formulation used for MALDI spot preparation to examine the impact the parameter has on analyte signal intensity. The results show that for five of six peptides tested across a wide mass range a formulation of approximately 75% acetonitrile is optimal for average MALDI signal intensity as determined on both time-of-flight and quadropole mass spectrometers. Examination of the individual spots shows that the organic solvent content in formulation significantly affects parameters such as crystal density and morphology.