Filtern
Erscheinungsjahr
Dokumenttyp
- Zeitschriftenartikel (15)
- Vortrag (1)
- Sonstiges (1)
- Posterpräsentation (1)
Sprache
- Englisch (16)
- Deutsch (1)
- Mehrsprachig (1)
Schlagworte
- Nanophotonics (3)
- Capillary discharge (2)
- Piezoelectricity (2)
- Polymer functionalization (2)
- Surface modification (2)
- Underwater plasma (2)
- Ageing of polyolefins (1)
- Amine derivatives (1)
- Anisotropie (1)
- Anti-oxidative efficiency (1)
Organisationseinheit der BAM
Eingeladener Vortrag
- nein (1)
Study of carboxylic functionalization of polypropylene surface using the underwater plasma technique
(2009)
Non-equilibrium solution plasma treatment of polymer surfaces in water offers the possibility of more dense and selective polymer surface functionalization in comparison to the well-known and frequently used low-pressure oxygen plasma. Functional groups are introduced when the polymer surface contacts the plasma moderated solution especially water solutions. The emission of ions, electrons, energy-rich neutrals and complexes, produced by the ion avalanche are limited by quenching, with the aid of the ambient water phase. The UV-radiation produced in plasma formation also helps to moderate the reaction solution further by producing additional excited, ionized/dissociated molecules. Thus, monotype functional groups equipped polymer surfaces, preferably OH groups, originating from the dissociated water molecules, could be produced more selectively. An interesting feature of the technique is its flexibility to use a wide variety of additives in the water phase. Another way to modify polymer surfaces is the deposition of plasma polymers carrying functional groups as carboxylic groups used in this work. Acetic acid, acrylic acid, maleic and itaconic acid were used as additive monomers. Acetic acid is not a chemically polymerizing monomer but it could polymerize by monomer/molecular fragmentation and recombination to a cross linked layer. The other monomers form preferably water-soluble polymers on a chemical way. Only the fragmented fraction of these monomers could form an insoluble coating by cross linking to substrate. The XPS analysis was used to track the alterations in -O-CO- bond percentage on the PP surface. To identify the -COOH groups on substrate surface unambiguously, which have survived the plasma polymerization process, the derivatization with trifluoroethanol was performed.
The interaction of microplastics with freshwater biota and their interaction with other stressors is still not very well understood. Therefore, we investigated the ingestion, excretion and toxicity of microplastics in the freshwater gastropod Lymnaea stagnalis.
MP ingestion was analyzed as tissues levels in L. stagnalis after 6–96 h of exposure to 5–90 μm spherical polystyrene (PS) microplastics. To understand the excretion, tissue levels were determined after 24 h of exposure followed by a 12 h–7 d depuration period. To assess the toxicity, snails were exposed for 28 d to irregular PS microplastics (<63 μm, 6.4–100,000 particles mL−1), both alone and in combination with copper as additional stressor. To compare the toxicity of natural and synthetic particles, we also included diatomite particles. Microplastics ingestion and excretion significantly depended on the particle size and the exposure/depuration duration. An exposure to irregular PS had no effect on survival, reproduction, energy reserves and oxidative stress. However, we observed slight effects on immune cell phagocytosis. Exposure to microplastics did not exacerbate the reproductive toxicity of copper. In addition, there was no pronounced difference between the effects of microplastics and diatomite. The tolerance towards microplastics may originate from an adaptation of L. stagnalis to particle-rich environments or a general stress resilience. In conclusion, despite high uptake rates, PS fragments do not appear to be a relevant stressor for stress tolerant freshwater gastropods considering current environmental levels of microplastics.
A guided drop test was performed to achieve a defined and reproducible impact orientation of jerrycans. The drop heights where 50% of the jerrycans experienced a failure from a crack where fluid can escape (50% failure drop height) were compared among jerrycans made of four different materials, in their original state and preconditioned with standard liquids. To analyse the impact of only elevated temperatures, the packages were preconditioned for 21?days at 40°C without the use of chemicals.
The 50% failure drop height was compared by using Young's modulus; the notched impact strength (NIS) of specimen cut from plates which were manufactured by compression moulding and the notched tensile impact strength of specimen cut-outs of the jerrycans' side walls. The NIS depends highly on the thermal preconditioning of the plates being manufactured by compression moulding. A trend can be seen that a higher Young's modulus, a higher NIS and a higher notched tensile impact strength result in a higher 50% failure drop height, but the values are spread. The influence of the wall thickness cannot be neglected.
The change of the 50% failure drop height in regard to the preconditioning at 40°C with and without nitric acid was compared in terms of their resistance to molecular degradation, density and degree of crystallinity. The conditioning at elevated temperature causes post-crystallization. It was shown that the resistance to molecular degradation determined on pressed plates correlates with the change of the 50% failure drop height after pre-storage with nitric acid.
It has been shown that selected types of substituents are able to vary the oxidative behavior of multi-walled carbon nanotubes. Such substituents investigated were sterically hindered secondary amino groups bonded in grafted piperidine units and covalently bonded bromine groups. Their interference and activity was preliminary determined in the model cumene and then in oil diesel fraction and low density polyethylene oxidation reactions. Results obtained indicate that chemical linking of amine moieties containing –NH groups directly to the carbon nanotubes core significantly increases their intrinsic anti-oxidative capacity while the grafting of Br-groups provokes the opposite functioning of the pristine samples. This inference was proved by thermogravimetric and differential thermal analysis of the polyethylene composites and experiments on profound aerobic oxidation of petroleum naphthenic fraction derived from the commercial Baku oils blend diesel cut.
The quenching and partitioning (Q&P) heat treatment enables a higher deformability of high strength martensitic steels. The Q&P heat treatment was applied on the martensitic stainless steel 1.4034 (X46Cr13) to study the influence of partitioning time. Therefore, extensive characterizations of the mechanical properties, focussing on the materials behaviour under different mechanical load scenarios, were performed. A comprehensive analysis of the microstructural evolution was per-formed for different heat treatment and mechanical loading states. A complete solution of chromium carbides was detected to be a first requirement for successful Q&P heat treatment. The comparison of common quenching and tempering with the Q&P heat treatment verifies the extensively enhanced materials strength whereat the formability is still acceptable. The microstructural reason was detected to be an increasing aus-tenite fraction due to austenite reversion at subgrain boundaries of martensite besides the stabilising of retained austenite. Further a distinctive strength differential effect was observed.
Recently, we suggested an unconventional approach [the so-called Internal-Field-Guarded-Active-Region Design (IFGARD)] for the elimination of the crystal polarization field induced quantum confined Stark effect (QCSE) in polar semiconductor heterostructures. And in this work, we demonstrate by means of micro-photoluminescence techniques the successful tuning as well as the elimination of the QCSE in strongly polar [000-1] wurtzite GaN/AlN nanodiscs while reducing the exciton life times by more than two orders of magnitude. The IFGARD based elimination of the QCSE is independent of any specific crystal growth procedures. Furthermore, the cone-shaped geometry of the utilized nanowires (which embeds the investigated IFGARD nanodiscs) facilitates the experimental differentiation between quantum confinement- and QCSE-induced emission energy shifts. Due to the IFGARD, both effects become independently adaptable.
One of the most significant limitations for the quantum efficiency of group III-nitride based light emitters is the spatial electron-hole separation due to the quantum-confined Stark effect (QCSE). To overcome this problem, Hönig et al. [1] proposed a novel concept, the Internal-Field-Guarded-Active-Region Design (IFGARD), which suppresses the QCSE for wurtzite crystals in the [0001] direction. Here, we show how encapsulating the active region by additional guard layers results in a strong reduction of the built-in electric field in c-plane wurtzite nanostructures. Even more importantly, we demonstrate the first experimental evidence for the successful realization of an IFGARD structure based on GaN/AlN heterostructures embedded in GaN nanowires. By means of power-dependent and time-resolved µ-photoluminescence (µ-PL) we experimentally proof the validity of the unconventional IFGARD structure. We managed to tune the emission of 4-nm-thick GaN nano-discs up to 3.32 eV at low excitation powers, which is just 150 meV below the bulk GaN bandgap. Our results demonstrate an almost complete elimination of the QCSE in comparison to conventional structures which show approximately 1 eV red-shifted emission. The suppression of the QCSE results in a significant increase of the radiative exciton decay rates by orders of magnitude and demonstrates the potential of IFGARD structures for future light sources based on polar heterostructures.
[1] Hönig et al., Phys. Rev. Applied 7, 024004 (2017)
Recently, we suggested an unconventional approach (the so-called Internal-Field-Guarded-Active-Region Design “IFGARD”) for the elimination of the quantum-confined Stark effect in polar semiconductor heterostructures. The IFGARD-based suppression of the Stark redshift on the order of electronvolt and spatial charge carrier separation is independent of the specific polar semiconductor material or the related growth procedures. In this work, we demonstrate by means of micro-photoluminescence techniques the successful tuning as well as the elimination of the quantum-confined Stark effect in strongly polar [000-1] wurtzite GaN/AlN nanodiscs as evidenced by a reduction of the exciton lifetimes by up to four orders of magnitude. Furthermore, the tapered geometry of the utilized nanowires (which embed the investigated IFGARD nanodiscs) facilitates the experimental differentiation between quantum confinement and Stark emission energy shifts. Due to the IFGARD, both effects become independently adaptable.