Veränderungen des dielektrischen Relaxationsspektrums von Hochpolymeren bei Verstreckung und Vorbehandlung Polycarbonat

Zusammenfassung Dielektrische Messungen an Polycarbonatproben von verschiedenem Verstreckungszustand und verschiedener Vorbehandlung zeigen Ver?nderungen des Relaxationsspektrums, die den Beobachtungen an anderen untersuchten Substanzen wie Polyamiden, Terylen etc. vollkommen entsprechen. Die Untersuchungen wurden seinerzeit mit den anderen Messungen zusammen durchgeführt, doch erfolgt die Ver?ffentlichung der Werte erst jetzt. Diese Ergebnisse lagen also schon 1956 zusammen mit denen aus Zit. 1 vor.     

Zur Frage der reduzierten Darstellung des dielektrischen Spektrums bei Hochpolymeren

Zusammenfassung Es wird aus dielektrischen Messungen am System Polyisobutyl?ther-Dekahydronaphthalin eine reduzierte Darstellung gewonnen. Je nach Art der angewandten Reduktion kann der Linienzug eine geschlossene Kurve oder eine streuende Kurvengruppe darstellen. Sofern aus ihm unter Verzicht auf Feinheiten eine übersicht über das Verhalten gewonnen werden soll, ist das Verfahren anwendbar. Einzelheiten jedoch, insbesondere über Ver?nderung der Verschmierung um den Schwerpunkt der Dispersionsstelle, gehen notwendigerweise verloren, sofern man sie nicht aus der sogenannten „shift“-Funktion oder der verbleibenden Streuung um die mittlere Kurve wieder herausliest. Wir dankendr Deutschen Forschungsgemeinschaft für Unterstützung Arbeit.     

Helmholtz resonator lined with absorbing material

A closed-form, two-dimensional analytical solution is developed to investigate the acoustic performance of a concentric circular Helmholtz resonator lined with fibrous material. The effect of density and the thickness of the fibrous material in the cavity is examined on the resonance frequency and the transmission loss. With the expressions for the eigenvalue and eigenfunction in the cavity, the transmission loss is obtained for a piston-driven model by applying a pressure/velocity matching technique. The results from the analytical methods are compared to the numerical predictions from a three-dimensional boundary element method and the experimental data obtained from an impedance tube setup. It is shown that the acoustic performance of a Helmholtz resonator may be modified considerably by the density and thickness of the fibrous material without changing the cavity dimensions.     

Cascade catalysis for the homogeneous hydrogenation of CO2 to methanol

This communication demonstrates the homogeneous hydrogenation of CO(2) to CH(3)OH via cascade catalysis. Three different homogeneous catalysts, (PMe(3))(4)Ru(Cl)(OAc), Sc(OTf)(3), and (PNN)Ru(CO)(H), operate in sequence to promote this transformation.     

Efficient reflection grisms for pulse compression and dispersion compensation of femtosecond pulses

Efficient reflection grisms for pulse-compression and material-dispersion compensation have been designed and demonstrated in a 40 fs, 300 microJ, 5 kHz downchirped pulse amplification system for the first time to our knowledge. A grism design for 800 nm femtosecond laser pulse dispersion compensation applications is realized by using standard, commercial diffraction gratings.     

Multi-Year Study of the Chemical and Sensory Effects of Microwave-Assisted Extraction of Musts and Stems in Cabernet Sauvignon,Merlot and Syrah Wines from the Central Coast of California

Microwave technology (MW) was applied to musts and stems over three consecutive vintages in Cabernet Sauvignon, Merlot and Syrah wines from California (USA). Stems were added to musts at a rate of 50 and 100% (50% Stems and 100% Stems), either as untreated or after MW (50% MW Stems and 100% MW Stems). Stem additions lowered ethanol (up to 1.15% v/v reduction), but increased pH (up to 0.16 units) and the tannin content of the wines. In 2016, tannins increased by 103% (100% Stems), and 124% (100% MW Stems). In 2017, tannins increased by 39% in stem-added Merlot wines and by 63% (100% Stems) and 85% (100% MW Stems) in Syrah wines. In 2018, tannins in Syrah wines increased by 250% (100% MW Stems) and by 743% (100% Stems). Wines made with 50% Stems exhibited intermediate tannin contents. Must MW increased flavonols (up to 278% in Syrah wines), monoglucosylated, acylated and anthocyanin-derived pigments. Stem additions reduced wine color and polymeric pigment formation in Syrah. Must MW decreased the perception of coarseness and herbaceous flavors in Merlot, whereas stem additions increased herbaceous aromas in Syrah. Despite higher tannin contents in stem-added wines, no concomitant increases in astringency were observed.     

Stretchable Gas Barrier Achieved with Partially Hydrogen‐Bonded Multilayer Nanocoating

Super gas barrier nanocoatings are recently demonstrated by combining polyelectrolytes and clay nanoplatelets with layer‐by‐layer deposition. These nanobrick wall thin films match or exceed the gas barrier of SiO_x and metallized films, but they are relatively stiff and lose barrier with significant stretching (≥10% strain). In an effort to impart stretchability, hydrogen‐bonding polyglycidol (PGD) layers are added to an electrostatically bonded thin film assembly of polyethylenimine (PEI) and montmorillonite (MMT) clay. The oxygen transmission rate of a 125‐nm thick PEI‐MMT film increases more than 40x after being stretched 10%, while PGD‐PEI‐MMT trilayers of the same thickness maintain its gas barrier. This stretchable trilayer system has an OTR three times lower than the PEI‐MMT bilayer system after stretching. This report marks the first stretchable high gas barrier thin film, which is potentially useful for applications that require pressurized elastomers.

     

Towards supramolecular polymers

The natural phenomenon of self-assembly has been used to make complex unnatural products. These new compounds have taken the form of catenanes and rotaxanes. We have identified several polymeric architectures containing the catenane and rotaxane motifs, and then described how the model structures, which we have identified and actually realized as chemical compounds, can be employed to assess the feasibility of introducing mechanical linkages into novel polymers by means of self-assembly processes.