Toughness optimization of elastomer‐modified glass–fiber reinforced PA6 materials

To investigate the influence of moisture and EPR‐g‐MA content on the fracture behavior of glass–fiber reinforced PA6 materials, brittle‐to‐tough transition temperatures (T_btt) were determined. Water absorption was taken into account by conditioning the analyzed materials. Tensile tests could reveal the temperature range of the largest moisture dependence of mechanical properties between 10 and 50°C. J‐integral values were used to describe the fracture behavior under conditions of impact load as a function of temperature. The brittle‐to‐tough transition of reinforced polyamides was found to be less approximate than in unreinforced materials. Two different characteristic temperature points T_s and T_e were identified, which were the intercept between elastic and elastic–plastic deformation on the one hand and the starting point of dominating stable crack propagation with strong plastic deformation on the other hand. Characteristic brittle‐to‐tough transition temperatures T_btt could be calculated as the arithmetic average of these two points. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Interfacial chemistry using a bifunctional coupling agent for enhanced electrical properties of carbon nanotube based composites

A bifunctional coupling agent (BCA) containing one oxazoline and one benzoxazinone group was applied to promote a reaction between polyamide 12 (PA12) and multiwalled carbon nanotubes (MWCNTs) during melt mixing. With this modification, the MWCNT content needed for the electrical percolation was significantly reduced by more than a factor of three. For amino functionalized MWCNT–PA12 composites adding 1 wt.% BCA electrical percolation was reached at only 0.37 wt.% MWCNTs compared to 1.0 wt.% without BCA. With the help of a model reaction, the covalent attachment of the BCA to the MWCNTs could be shown by thermogravimetric analysis (TGA) and via fluorescence spectroscopy. Model compounds were applied containing either only the oxazoline or the benzoxazinone group to show that the better electrical properties in the PA12–MWCNT composites were a result of a covalent bond between the polymer and the nanotube which only takes place when the BCA was used. In addition, significantly higher electrical conductivity values were obtained by the addition of BCA as well with amino functionalized as with nonmodified commercial MWCNTs. This surprising result was attributed to the significant hydroxy group content on the surface of those commercial MWCNTs.     

On Limitations of Structured (Deterministic) DNNFs

Theory of Computing Systems - The study of representations for propositional theories has been a central subject in knowledge compilation. Many known representations of propositional knowledge...     

ZnMgSSe/ZnSSe/ZnSe-heterostructures grown by metalorganic vapor phase epitaxy

ZnMgSSe heterostructures have been grown in a low-pressure metalorganic vapor phase epitaxy system with the precursors dimethylzinc triethylamine, ditertiarybutylselenide, tertiarybutylthiol, and biscyclopentadienylmagnesium at 330°C and a total pressure of 400 hPa. The optimization of the single layers was carried out by means of low temperature photoluminescence. Only the near band edge emission was observable with negligible deep levels. The heterostructures consisting of a triple ZnSe quantum well showed intense luminescence which hints at an effective carrier confinement. Scanning transmission electron microscopy investigations of the heterostructures still showed structural detects since the layers were not lattice matched to the GaAs substrate yet.     

Tailoring the Morphology of Responsive Bioinspired Bicomponent Fibers

Nature is an intriguing inspiration for designing a myriad of functional materials. However, artificial mimicking of bioinspired structures usually requires different specialized procedures and setups. In this study, a new upscalable concept is presented that allows to produce two bioinspired, bicomponent fiber morphologies (side‐by‐side and coaxial bead‐on‐string) using the same electrospinning setup, just by changing the employed spinning solvent. The generated fiber morphologies are highly attractive for thermoresponsive actuation and water harvesting. Another challenge solved in this work is the compositional characterization of complex fiber morphologies. Raman imaging and atomic force microscopy is introduced as a powerful method for the unambiguous characterization of complex bicomponent fiber morphologies. The work opens the way for the construction of heterostructured fiber morphologies based on different polymers combinations, offering high potential for applications as actuators, smart textiles, water management, drug release, and catalysis.     

Realizability of concurrent recursive programs

We study the realizability problem for concurrent recursive programs: given a distributed system architecture and a sequential specification over words, find a distributed automata implementation that is equivalent to the specification. This problem is well-studied as far as finite-state processes are concerned, and it has a solution in terms of Zielonka’s Theorem. We lift Zielonka’s Theorem to the case where processes are recursive and modeled as visibly pushdown (or, equivalently, nested-word) automata. However, contrarily to the finite-state case, it is undecidable whether a specification is realizable or not. Therefore, we also consider suitable underapproximation techniques from the literature developed for multi-pushdown systems, and we show that they lead to a realizability framework with effective algorithms.     

Macroscopic and microscopic monitoring of swelling of beech wood after impregnation with furfuryl alcohol

Wood furfurylation is a modification method that improves several wood properties. Thereby wood is impregnated with a solution of furfuryl alcohol, catalysts and water, in general. The objective of this study was to understand the penetration of furfuryl alcohol into wood. Furthermore, a possible relationship between the substance amount and the swelling behaviour should be determined. To this end microscopic investigations were conducted to describe the temporal process of penetration and swelling. It was found that the swelling coefficients differ at the microscopic and macroscopic level. The microscopic swelling can reach twice the values of macroscopic swelling.     

Passive sampling combined with ecotoxicological and chemical analysis of pharmaceuticals and biocides - evaluation of three Chemcatcher™ configurations

Passive sampling is a tool to monitor the presence and concentrations of micropollutants in the aquatic environment. We investigated the duration of integrative sampling and the effects of flow rate on the performance of three configurations of the Chemcatcher - a sampler for polar organic compounds. Chemcatchers were fitted with Empore™ styrenedivinylbenzene (SDB) XC disks (XC), SDB-RPS disks (RPS) or SDB-RPS disks covered with a polyethersulfone membrane (RPS-PES). Samplers were either exposed to treated sewage effluent for 5 days at various flow rates, or at a single flow rate with overlapping exposures of 3-24 days. Chemical analysis focused on a set of pharmaceuticals and biocides and ecotoxicological analysis measured inhibition of photosystem II in algae. For compounds with log K_OW > 2, both XC and RPS disks respond dynamically to higher flow rates; uptake increased up to five-fold when flow increased from 0.03 to 0.37 m s⁻¹. At a flow rate of 0.13 m s⁻¹ the integrative window of SDB disks approached 6 days for more hydrophobic compounds (log K_OW > 3.5). The RPS-PES configuration was less affected by flow and also showed an extended integrative window (up to 24 days). The membrane causes a lag phase of up to 2.3 days which thwarts a sound interpretation of data from sampling periods of less than 10 days.     

Effect of polymorphism of isotactic polybutene‐1 on peel behavior of polyethylene/polybutene‐1 peel systems

The effect of polymorphism of isotactic polybutene‐1 (iPB‐1) on the peel behavior of the specific peel system low‐density polyethylene/polybutene‐1 (LDPE/iPB‐1) was investigated using wide‐angle X‐ray scattering, calorimetry, and the T‐peel test. Melt‐crystallization of iPB‐1, initially, yields tetragonal form II crystals which transform as a function of time to trigonal form I crystals. The kinetics of transformation at ambient temperature follows an exponential function, and is completed after about 50–75 h. The presence of LDPE in the peel system does not affect the transformation kinetics. The structure of the crystalline phase of iPB‐1 controls the peel force which decreases by about 25% during the crystal–crystal transformation in a blend with 20m% iPB‐1. The reduction of the peel force depends linearly on the mass fraction of iPB‐1 crystals in the peel system which further evidences the correlation between the crystal–crystal transformation of iPB‐1 and the peel‐characteristics of LDPE/iPB‐1 blends. Isothermal reorganization of crystals of LDPE is excluded as reason for the change of the peel‐performance of LDPE/iPB‐1 blends, since it is 5 to 10 times faster than the decrease of the peel force, and crystal–crystal transformation of iPB‐1, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008