Publikationen

In this paper we systematically investigated effect of separator morphology on the performance of Li-S batteries. We tested two kinds of commercially available non-woven fibrous separators made of polypropylene in conjunction with trilayer PP/PE/PP porous separator. Among the non-woven separators, the fibers of the separator of first kind are rough and more acidic than the fibers of the separator of second art, which are smooth. It was found that batteries with smooth separator demonstrate higher Coulombic efficiency, higher charging/discharging capacity and better cycling stability. We attribute better performance of batteries with smooth fibers of separators to lower acidity than that of rough fibers. We believe that negatively charged polysulfides are unable to adsorb on more acidic rough fibers and diffuse readily to lithium electrode. In contrast, polysulfides are able to adsorb on the surface of less acidic smooth fibers that reduces their polysulfides shuttle and rapid decay of battery capacity. Strategic deployment of non-woven Freudenberg and Celgard separator in combination leads to high active mass utilization, superior wettability, reduced short circuit tendency caused by dendritic growth and slower capacity decay.

A stretchable gel-polymer electrolyte (GPE) based on polyepichlorohydrin terpolymer as a host polymer, a mixture of 1,3-dioxolane and 1,2-dimethoxyethane as plasticizers and lithium bis(trifluoromethane)sulfonimide (LiTFSI) as salt was developed and studied in detail. GPEs were prepared in a two-step process. The cross-linked polyepichlorohydrin network was developed using ethylene thiourea (ETU) and magnesium oxide (MgO) as cross-linkers. An immersion method was used for distribution of LiTFSI-salt in the network film. The effects of electrolyte uptake on mechanical and thermal properties of GPEs were studied in detail. Dynamic mechanical analysis (DMA) shows a GPE with a storage modulus higher than 0.6 MPa at ambient temperature (298 K). Differential scanning calorimetry (DSC) analysis was carried out on the GPE to demonstrate the change in glass transition temperature caused by the addition of two plasticizers. Impedance spectroscopy was used to study the ionic conductivity in the GPE. The highest ionic conductivity was found to be 2.4 × 10−4 S/cm at 298 K. The lithium-sulfur cells in conjunction with the elastomeric gel-polymer electrolyte showed characteristic cyclic voltammograms and charge-discharge plateaus indicating a two stage reduction process and a one stage oxidation process. The battery demonstrated initial specific capacity of 700–800 mA h/gsulfur which faded slowly with cycle number. Our present work could pave a new route to fabricate flexible rechargeable batteries with a cross-linked soft polymer electrolyte.

Wegen der vorteilhaften Eigenschaften im Trockenlauf sind thermoplastische Kunststoffe bereits in vielen tribologischen Anwendungen vertreten, hohe Temperaturen führen den Werkstoff dabei jedoch schnell an seine Grenzen. In dieser Studie wird der Wärmeentwicklung im tribologischen Kontakt durch einen energieabsorbierenden Füllstoff entgegengewirkt. Mechanische, thermische und tribolo-gische (Pin-on-Disk) Prüfungen zeigen deutlich, dass durch Nutzung energieverzehrender Effekte das Einsatzfeld kunststoffbasierter Tribocompounds stark erweitert werden kann.

A ball-milling approach was developed to investigate the constituents of isolated nacre tablets of the gastropod Haliotis glabra in aqueous suspension without additional chemical additives. The obtained particle mixtures were characterized using X-ray crystallography as well as scanning and transmission electron microscopy. Aragonite nanoparticles retained their crystal structure even after 14 h of ball milling. The long-term stability of the particle mixtures varied as a function of the ball-milling duration. An increased milling time led to rod-like stable assemblies of aragonite nanoparticles. Selected area electron diffraction investigations revealed that the longitudinal axes in about one-third of these nanoparticle rods were oriented along the crystallographic c-axis of aragonite, indicating oriented attachment of the aragonite nanoparticles. These in vitro observations support the idea that a two-stage process, separated into crystallization of nanoparticles and oriented assembly of nanocrystals, could also occur in vivo.

ABSTRACT Polycarbonate (PC) nanocomposites containing different nano-SiO2 contents were prepared using a twin-screw extruder followed by injection molding. The mechanical behavior and environmental stress cracking (ESC) resistance of the nanocomposites were investigated. Compared to neat PC, the incorporation of nanofiller leads to a slight improvement in Young's modulus, tensile strength, and notched impact strength properties. Interestingly, the nanofiller enhanced the environmental stress cracking resistance of PC in different fluids (isopropanol, methanol, aqueous urea solution, and deionized water) vastly. The correlation of the mode I critical stress intensity factor with the Hansen solubility parameter shows a very good agreement for different fluids and thus allows the prediction of the stress cracking behavior as a function of the filler content for different stress-cracking agents. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45451.

The cyclic tert-butyl-amino alane dimer [tBu–N(H)AlH2]2 (1) was obtained from reaction between alane with tert-butylamine and its boranate derivative [tBu–N(H)–Al(BH4)2)]2 (2) subsequently from 1 by hydride/chloride exchange using PbCl2 followed by reaction with LiBH4. Both compounds form four-membered Al2N2 cycles with typical Al–N bond lengths of 1.940(5) Å (1) and 1.945(5) Å (2) as found from X-ray diffraction analysis. The tert-butyl substituents at the nitrogen atoms may be situated at the same side of the ring (cis) or at opposite sides (trans). For compound 1 both isomers are present in solution, showing particular temperature dependent NMR shifts. In the solid both compounds 1 and 2 adopt the trans arrangement. When 1 is reacted with PbCl2 in half of the molarity ratio used for 2, surprisingly the novel compound 3, a zwitterion, can be obtained: [(tBu–N)(Al–H)3(tBu–N(H))3Cl((H)N–tBu)3(Al–H)2(Al–Cl)(N–tBu)]+[(tBu–N)(tBu–N(H))(AlCl2)2]–. X-ray structure analysis reveals that the anion is made of a tert-butyl amino aluminum dichloride dimer (central Al2N2 ring) with one of the two nitrogen atoms being deprotonated. The cationic counterpart consists of three entities: (i) There is a first seco-norcubane like Al3N4 basket with tert-butyl groups at the nitrogen atoms, two hydride and one chloride ligand at the aluminum atoms and three hydrogen atoms on the open side of the basket, all pointing in the same direction; (ii) There is a second similar Al3N4 basket with the same substituent pattern except that all aluminum atoms have exclusively hydrogen ligands; (iii) Both baskets coordinate a central chloride through the six protons at the open nitrogen face of the baskets in such a way that the chloride lies in the center of a H6 trigonal anti-prism [mean H–Cl–H = 56.1(9)°]. As each of the open cages has a positive charge the overall charge by combination with the chloride adds to +1. The structure of the cationic part of 3 is unprecedented in AlN polycycles.

Here, we describe a simple method to prepare oil-repellent surfaces with inherent reactivity. Liquid-like copolymers with pendant reactive groups are covalently immobilized onto substrates via a sequential layer-by-layer method. The stable and transparent nanocoatings showed oil repellency to a broad range of organic liquids even in the presence of reactive sites. Functional molecules could be covalently immobilized onto the oil-repellent surfaces. Moreover, the liquid repellency can be maintained or finely tailored after post-chemical modification via synergically tailoring the film thickness, selection of capping molecules, and labeling degree of the capping molecules. Oil-repellent surfaces that are capable of post-functionalization would have technical implications in surface coatings, membrane separation, and biomedical and analytical technologies.

Liquid-based mobile interfaces, in which liquids are being utilized as structural long-term components, have shown their multifunctionality in materials science, such as the hydration layer of polyelectrolyte brushes used for artificial implants, stabilized lubricants for antibiofouling, anti-icing, self-cleaning, optical control, and so forth. However, these currently available systems do not usually show a response to environmental stimuli. Here, we describe a strategy for preparing thermoresponsive mobile interfaces made from novel silicone-based lubricants that display lower critical solution temperature and demonstrate their capabilities on controlling in situ water wetting and dewetting, thermo-gating penetration, and optical properties. These properties allow the mobile films to form a kind of erasable recording platforms. We foresee diverse applications in liquid transport, wetting and adhesion control, and transport switching.

Gelation-mediated phase separation is applied to prepare immiscible polymer bilayer films with an interlocking interface structure. Polymer systems consisting of copolymer of urea and polydimethylsiloxane and epoxy are selected to demonstrate the feasibility. When the epoxy fraction exceeds 25 wt%, well-defined bilayer structures self-form by a one-pot casting method in which the phase separation state is fixed by an evaporation-induced gelation. Microscopy studies of the resulting bilayers clearly reveal that interlocking structures form during the bilayer films construct. The interlocking structures lead to an enhanced interfacial adhesion and higher fracture energy. The current strategy might offer a facile way to in situ create an interlocking interface between immiscible polymer systems.