Thermal Decomposition of Polytetrafluoroethylene Oxide

The thermal degradation of polytetrafluoroethylene oxide has been examined by the isothermal and thermogravimetric methods in the temperature range 450 to 650°C. The main components of the volatile gas are trifluoro-acetyl fluoride, carbonyl fluoride, and tetrafluoroethylene. The thermogravimetric decompositions of polytetrafluoroethylene oxide and of polytetrafluoroethylene have been compared.     

A perturbed gamma degradation process with degradation dependent non‐Gaussian measurement errors

This paper proposes and illustrates a new perturbed gamma degradation process where the measurement error is modeled as a non‐Gaussian random variable that depends stochastically on the actual degradation level. The expression of the likelihood function for a generic set of noisy degradation measurements is derived, and the expression of the remaining useful life distribution of a degrading unit that fails when its degradation level exceeds a given threshold limit is formulated. A particle filter method is suggested, which allows one to compute the likelihood function and to estimate the remaining useful life distribution in a quick yet efficient manner. In addition, a closed‐form approximation of the perturbed gamma process is proposed to use in the special, yet meaningful, case where the standard deviation of the measurement error depends linearly on the actual degradation level. Finally, an applicative example is discussed, where the parameters of the perturbed gamma process, the remaining useful life distribution, and the mean remaining useful life of the degrading units are estimated from a set of noisy real degradation data.     

Laser photolysis of chlorodiaminotriazines and detection of their fragmentation and clusterization products

The laser photolysis of three 2-chloro-4-6-diamino-1,3,5-triazines, namely simazine, atrazine and propazine, was investigated. The products formed were detected by time-of-flight mass spectromety. The results illustrate that the main process is fragmentation competing with cluster formation. The hydrogen bonding proposed for the crystal structure of diaminotriazines should be responsible for the gas-phase clusterization occurring by laser ablation.     

Kinetics,mechanism, and stereochemistry of Diels-Alder reactions of carbonyl-substituted ethenes with cyclohexa-1,3-diene in the gas phase

The kinetics of the Diels–Alder additions of CH₂ ? CHCHO, CH₂? C(CH₃)CHO, and CH₂? CHC(CH₃)O to cyclohexa-1,3-diene (CHD) have been studied in the gas phase. The stereochemistry and the mechanism of these reactions are discussed. In contrast with other Diels–Alder additions involving CHD as diene, a biradical mechanism does not fit the experimental results.     

Effect of covalent functionalization of C60 fullerene on its encapsulation by water soluble calixarenes

The molecular encapsulation of functionalized fullerenes (substituted fulleropyrrolidines) with water-soluble calixarenes was studied by photoluminescence and quantum-chemical methods. The results show that both the thiacalix[4]arene-tetrasulfonate and calix[6]arene-hexasulfonate are able to overcome the natural water-repulsive character of fullerenes. However, the functionalization of calixarenes and fullerenes induces significant changes in the molecular encapsulation processes, and the obtained thermodynamic behavior of the complex formation highlights the importance of the entropy. Our results can contribute to the development of the synthesis and design of functionalized calixarenes supporting their application in pharmaceutical and food chemistry.     

Ultraviolet-based bonding for perfluoropolyether low aspect-ratio microchannels and hybrid devices

Producing solvent-resistant microfluidic devices is a challenge for analytical chemistry and biochemistry. We demonstrate a simple and low-cost fabrication approach for the realization of solvent-resistant microchannels based on perfluoropolyether elastomers, exhibiting very low aspect ratios (0.01). The strength of the microchannels sealing is evaluated through the maximum internal pressure (1.52 MPa) prior to device failure, due to delamination at the bonded interface. This approach allows the elastic properties of silicone elastomers, suitable for high quality external connections, to be combined with the non-swelling character of perfluoropolyethers.     

The Role of Drug–Drug Interactions in Hydrogel Delivery Systems: Experimental and Model Study

To address the increasing need for improved tissue substitutes, tissue engineering seeks to create synthetic, three‐dimensional scaffolds made from polymeric materials able to incorporate cells and drugs. The interpretation of transport phenomena is a key step, but comprehensive theoretical data is still missing and many issues related to these systems are still unsolved. In particular, the contribution of solute–solute interactions is not yet completely understood. Here, we investigate a promising agar–carbomer (AC) hydrogel loaded with sodium fluorescein (SF), a commonly used drug mimetic. The self‐diffusion coefficient of SF in AC formulations was measured by using high resolution magic angle spinning NMR spectroscopy (HR‐MAS NMR). Starting from experimental data, a complete overview on SF transport properties is provided, in particular a mathematical model that describes and rationalizes the differences between gel and water environments is developed and presented. The hydrogel molecular environment is able to prevent SF aggregation, owing to the adsorption mechanism that reduces the number of monomers available for oligomer formation at low solute concentration. Then, when all adsorption sites are saturated free SF molecules are able to aggregate and form oligomers. The model predictions satisfactorily match with experimental data obtained in water and the gel environment, thus indicating that the model presented here, despite its simplicity, is able to describe the key phenomena governing device behavior and could be used to rationalize experimental activity.     

Topological insulators in three dimensions

We study three-dimensional generalizations of the quantum spin Hall (QSH) effect. Unlike two dimensions, where a single Z2 topological invariant governs the effect, in three dimensions there are 4 invariants distinguishing 16 phases with two general classes: weak (WTI) and strong (STI) topological insulators. The WTI are like layered 2D QSH states, but are destroyed by disorder. The STI are robust and lead to novel "topological metal" surface states. We introduce a tight binding model which realizes the WTI and STI phases, and we discuss its relevance to real materials, including bismuth.     

Phase transformations in aqueous low molar mass poly(vinyl methyl ether) solutions: theoretical prediction and experimental validation of the peculiar solvent melting line, bimodal LCST, and (adjacent) UCST miscibility gaps

Supported by theoretical predictions based on the Wertheim Lattice Thermodynamic Perturbation Theory, modulated temperature differential scanning calorimetry (MTDSC) was used to further the knowledge of the phase behavior of aqueous poly(vinyl methyl ether) (PVME) solutions. Using a narrowly dispersed low molar mass PVME, we determined the following phase boundaries: (i) a bimodal lower critical solution temperature (LCST) miscibility gap at physiological temperature (around 37 degrees C), (ii) an upper critical solution temperature (UCST) two-phase area at sub-zero temperatures and high polymer concentration, and (iii) the melting line of the solvent across the entire concentration range, showing a peculiar stepwise decrease with composition. The location of the glass transition region and its influence on the crystallization/melting behavior of the solvent is discussed.     

Corrosion of Ni in 1-butyl-1-methyl-pyrrolidinium bis (trifluoromethylsulfonyl) amide room-temperature ionic liquid: an in situ X-ray imaging and spectromicroscopy study

This paper reports a pioneering application of soft X-ray scanning transmission microscopy (STXM), combined with micro-spot X-ray absorption spectroscopy (XAS) and X-ray fluorescence spectroscopy (XRF), for the investigation of the corrosion of metal electrodes in contact with room-temperature ionic liquids (RTIL). Using an open electrochemical cell in vacuo we explore some fundamental aspects of the aggressiveness of the 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)amide ([BMP][TFSA]) RTIL towards Ni under in situ electrochemical polarisation. The possibility of imaging electrochemically-induced morphological features in conjunction with micro-XAS and XRF spectroscopies has provided unprecedented details regarding the space distribution and chemical state of corrosion products.