Above,below, and in‐between the two glass transitions of ultrathin free‐standing polystyrene films: Thermal expansion coefficient and physical aging

In previous work we observed two simultaneous transitions in high molecular weight (MW) free‐standing polystyrene films that were interpreted as two thickness‐dependent reduced glass transition temperatures (T_gs). The weaker lower transition agreed well with the MW‐dependent T_g(h) previously reported, while the much stronger upper transition matched the MW‐independent T_g(h) previously observed in low‐MW free‐standing films. Here, we investigate the nature of these two transitions by inspecting the temperature dependence of the films' thermal coefficient of expansion (TCE) and present physical aging measurements using ellipsometry both below and in‐between the two transitions. TCE values indicate approximately 80 to 90% of the film solidifies at the upper transition, while only 10 to 20% remains mobile to lower temperatures, freezing out at the lower transition. Physical aging is observed at a temperature below the upper transition, but above the lower transition, indicative of the upper transition being an actual glass transition associated with the α‐relaxation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 64–75     

Crosslinked poly(ethylene oxide) containing siloxanes fabricated through thiol‐ene photochemistry

Homogenous amphiphilic crosslinked polymer films comprising of poly(ethylene oxide) and polysiloxane were synthesized utilizing thiol‐ene “ click ” photochemistry. A systematic variation in polymer composition was Carried out to obtain high quality films with varied amount of siloxane and poly(ethylene oxide). These films showed improved gas separation performance with high gas permeabilities with good CO₂/N₂ selectivity. Furthermore, the resulting films were also tested for its biocompatibility, as a carrier media which allow human adult mesenchymal stem cells to retain their capacity for osteoblastic differentiation after transplantation. The obtained crosslinked films were characterized using differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis, FTIR, Raman‐IR , and small angle X‐ray scattering. The synthesis ease and commercial availability of the starting materials suggests that these new crosslinked polymer networks could find applications in wide range of applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1548–1557     

An inverse problem for infinitely divisible moving average random fields

Statistical Inference for Stochastic Processes - Given a low frequency sample of an infinitely divisible moving average random field $$\{\int _{\mathbb {R}^d} f(x-t)\varLambda (dx); \ t \in \mathbb...     

Three‐Dimensional Metal–Fullerene Frameworks

Hexakis‐substituted [60]fullerene adducts with icosahedral symmetry provide an unprecedented scaffold for the spatial arrangement of twelve functional groups with high geometric precision. This unique molecular symmetry identifies such polyfunctional organic building blocks as potential highly connective linkers for coordination polymer and metal–organic framework synthesis. Hereby, the linker exhibits a higher connectivity than the metal ions and with the main connectivity based on the ligand, this can create a new type of inversely cross‐linked framework. Two hexakis adducts bearing either twelve glycolic acid or 3‐hydroxypropionic acid side chains attached to its malonate units were incorporated as organic connectivity centers in the first fullerene‐containing three‐dimensional frameworks by coordination with Zn²⁺.     

Extending N-heterocyclic carbene ligands into the third dimension: a new type of hybrid phosphazane/NHC system

A simple, “click” synthetic approach to a new type of hybrid phosph(III)azane/NHC system is described. The presence of the phosphazane P₂N₂ ring unit, with P atoms flanking the NCN fragment and with this ring perpendicular to the binding site of the NHC, provides unique opportunities for modifying the electronic and steric character of these carbenes.     

Shock wave kinetics of Fe + NO based on Fe, O, and N atom measurements

The reaction of Fe atoms with NO was studied behind incident shock waves in the temperature range of 780–1,020 K at pressures between 0.3 and 1.2 bar. Atomic-resonance-absorption spectroscopy (ARAS) was applied for the time-resolved measurement of Fe , N, and O atoms in gas mixtures containing Fe(CO)₅ and NO, highly diluted in argon. The experiments showed a Fe-atom consumption without an associated O- or N-atom formation which can be explained by a recombination of Fe and NO:

Stoßwellen in Gas-Partikel-Gemischen mit Massenaustausch zwischen den Phasen

Zusammenfassung Die Nichtgleichgewichts-Austauschprozesse, die in einem Gas-Partikel-Gemisch hinter einer Stoßwelle ablaufen, werden in dieser Arbeit untersucht. Sie werden sowohl mit den Erhaltungsgleichungen für zwei interaktive Kontinua als auch mit den vereinfachten Gleichungen für Einzelpartikel in einem Gaskontinuum beschrieben. Der besondere Akzent liegt auf den Transportvorgängen sehr kleiner Partikel, die im Übergangsbereich zwischen Kontinuumsbedingungen und freier Molekülströmung stattfinden. Sie werden durch einfache Knudsenzahlansätze berücksichtigt. Beispiele zeigen die Geschwindigkeits-, Temperatur- und Partikelgrößenrelaxation hinter Stoß-wellen in Argon mit DOP-Tröpfchen und mit festen NaCl-Salzpartikeln.

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Shock waves in gas-particle mixtures with mass transfer between the phases

The nonequilibrium transfer processes, which take place in a gas-particle mixture behind shock waves, are investigated in this study. They will be described both by the conservation equations of two interactiv continua and by the simplified equations of a single particle in a gas continuum. The special accent is on exchange processes of very small particles, which take place in the transition regime between continuum and free molecular conditions. They are taken into account by simple Knudsen number corrections. Examples show the velocity, the temperature and the particle size relaxation behind shock waves in argon containing DOP droplets or solid NaCl particles.

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Die Arbeit entstand im Rahmen des Sonderforschungsbereiches SFB 209 Stoff- und Energietransport in Aerosolen der Universität — GH — Duisburg. Die Autoren danken der Deutschen Forschungsgemeinschaft für die finanzielle Unterstützung     

A shock tube study on the thermal decomposition of CS2 based on S(3P) and S(1D) concentration measurements

The thermal decomposition of CS₂ highly diluted in Ar was studied behind reflected shock waves by monitoring time-dependent absorption profiles of S(³P) and S(¹D) using atomic resonance absorption spectroscopy (ARAS). The rate coefficient of the reaction: