6 Materialchemie
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- 6 Materialchemie (116)
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- 6.6 Physik und chemische Analytik der Polymere (27)
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- 6.5 Synthese und Streuverfahren nanostrukturierter Materialien (9)
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- 5 Werkstofftechnik (5)
- 5.1 Mikrostruktur Design und Degradation (3)
- 6.7 Materialsynthese und Design (3)
Thin films (200-7nm) of the asymmetric polymer blend poly(vinyl methyl ether) (PVME)/polystyrene (PS) (25/75wt%) were investigated by broadband dielectric spectroscopy (BDS). Thicker samples ([Formula: see text]37 nm) were measured by crossed electrode capacitors (CEC), where the film is capped between Al-electrodes. For thinner films ([Formula: see text]37 nm) nanostructured capacitors (NSC) were employed, allowing one free surface in the film. The dielectric spectra of the thick films showed three relaxation processes ( [Formula: see text] -, [Formula: see text] - and [Formula: see text] -relaxation), like the bulk, related to PVME fluctuations in local spatial regions with different PS concentrations. The thickness dependence of the [Formula: see text] -process for films measured by CECs proved a spatially heterogeneous structure across the film with a PS-adsorption at the Al-electrodes. On the contrary, for the films measured by NSCs a PVME segregation at the free surface was found, resulting in faster dynamics, compared to the CECs. Moreover, for the thinnest films ([Formula: see text]26 nm) an additional relaxation process was detected. It was assigned to restricted fluctuations of PVME segments within the loosely bounded part of the adsorbed layer, proving that for NSCs a PVME enrichment takes place also at the polymer/substrate interface.
We present the optical sensing of phthalate Esters (PAEs), a group of endocrine-disrupting chemicals. The sensing takes place as changes in the fluorescence emission intensity of aminopyrene covalently bound to the organic ligands of the metal−organic framework compound ZIF-8. In the presence of PAEs, a quenching of the fluorescence emission is observed. We evaluated strategies to engineer colloidal size distribution of the sensing particles to optimize the sensory response to PAEs. A thorough characterization of the modified ZIF-8 nanoparticles included powder X-ray diffractometry, transmission electron microscopy, high-performance liquid chromatography, and photophysical characterization. The presented capability of the fluorophore-functionalized ZIF-8 to sense PAEs complements established methods such as chromatography-based procedures, which cannot be used on-site and paves the way for future developments such as hand-held quick sensing devices.
Copper has a strong bactericidal effect against multi-drug resistant pathogens and polyethers are known for their resistance to biofilm formation. Herein, we combined Cu nanoparticles (NPs) and a polyether Plasma polymer in the form of nanocomposite thin films and studied whether both effects can be coupled. Cu NPs were produced by magnetron sputtering via the aggregation in a cool buffer gas whereasolyether layers were synthesized by Plasma-Assisted Vapor Phase Deposition with poly(ethylene oxide) (PEO) used as a precursor. In situ specific heat spectroscopy and XPS analysis revealed the formation of a modified polymer layer around the NPs which propagates on the scale of a few nanometers from the Cu NP/polymer interface and then transforms into a bulk polymer phase. The chemical composition of the modified layer is found to be ether-deficient due to the catalytic influence of copper whereas the bulk polymer Phase exhibits the chemical composition close to the original PEO. Two cooperative glass transition phenomena are revealed that belong to the modified polymer layer and the bulk phase. The former is characterized by constrained mobility of polymer segments which manifests itself via a 30 K increase of dynamic glass transition temperature. Furthermore, the modified layer is characterized by the heterogeneous structure which results in higher fragility of this layer as compared to the bulk phase. The Cu NPs/polyether thin films exhibit reduced Protein adsorption; however, the constrained segmental dynamics leads to the Deterioration of the non-fouling properties for ultra-thin polyether coatings. The films are found to have a bactericidal effect against multi-drug resistant Gram-positive Methicillin-Resistant Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa.
A comparison of tributyltin chloride, dibutyltin dichloride,and butyltin trichloride as catalysts of ring-opening polymerizations(ROPs) of l-lactides at 160°C in bulk reveals increasing reactivity in the above order, but only the least reactive catalysts, Bu3SnCl, yield a uniform reaction product, namely cyclic poly(L-lactide)s with weight average molecular weights (Mw ́s) in the range of 40,000–80,000. A comparison of dimethyltin , dibutyltin , and diphenyltin dichlorides resulted in the following order of reactivity: Me2SnCl2<Bu2SnCl2<<Ph2SnCl2. In this series also, the most reactive catalyst yields cyclic polylactides, but the extent of cyclization varies with the molecular weight. The formation of cyclic polylactides is explained by ROP combined with simultaneous polycondensation involving end-to-end cyclization (ROPPOC method). ROP of meso-lactide at 80 or 60°C yields even-numbered linear chains as main products, a result supporting the ROPPOC mechanism.
We report on the ferromagnetism of Sn1-xZnxO2 (x < 0.1) hierarchical nanostructures with various morphologies synthesized by a solvothermal route. A room temperature ferromagnetic and paramagnetic response was observed for all compositions, with a maximum in ferromagnetism for x = 0.04. The ferromagnetic behaviour was found to correlate with the presence of zinc on substitutional Sn sites and with a low oxygen vacancy concentration in the samples. The morphology of the nanostructures varied with zinc concentration. The strongest ferromagnetic response was observed in nanostructures with well-formed shapes, having nanoneedles on their surfaces. These nanoneedles consist of (110) and (101) planes, which are understood to be important in stabilizing the ferromagnetic defects. At higher zinc concentration the nanostructures become eroded and agglomerated, a phenomenon accompanied with a strong decrease in their ferromagnetic response. The observed trends are explained in the light of recent computational studies that discuss the relative stability of ferromagnetic defects on various surfaces and the role of oxygen vacancies in degrading ferromagnetism via an increase in free electron concentration.
Size-exclusion chromatography (SEC) was used to monitor changes of the molecular masses of thermoplastic polyether – and polyester urethane (TPU) exposed to thermal, hydrolytic, and photo-oxidative (UV) Degradation conditions for several days. The thermal treatment was performed at elevated temperatures (100–200 °C) under oxidative (air) as well as non-oxidative (nitrogen) conditions to evaluate the specific influence of oxygen on the degradation. At higher temperatures (≥175 °C) a fast decrease of the molecular masses of both PU accompanied by a high degree of crosslinking was found. At lower temperatures (≤150 °C) the polymers remained widely unaffected by thermal degradation within the investigated degradation interval of up to two weeks. Surprisingly, the influence of oxygen (air) was found to be less distinct. In contrast to that, UV treatment at 25 °C at less than 10% rel. humidity (RH) resulted in a fast crosslinking, whereas the molecular masses of both PU decreased slower than for thermal treatments. The depth of penetration of the UV radiation was estimated using 3D printed PU samples with different thicknesses. Hydrolysis based degradation effects were less significant. Only slight molecular mass changes were detected at temperatures ≤80 °C within a time span of 14 days, while no crosslinking could be measured. Considering the degradation results at the investigated exposure parameters, it could be shown that esterbased PU in general exhibits a significant higher stability compared to ether-based materials.
We found previously how to estimate the density of the adsorbed surface species in the case of the molecules interacting to the oxide support surface by one type of bond. Here this algorithm is developed for the case of the molecules which can be bonded to the support surface by two types of bonds. The adsorption assumptions are similar to those considered in the case of only one type of bond. The calculation is exemplified for some composites of cyanophenyl alkylbenzoates (CPnBs) (n is the number of carbon atoms in the alkyl chain) interacting with Aerosil A380. The interaction takes place by hydrogen bonding between the –OH groups or the support and the functional groups of the CPnB molecules. The estimated values of the total surface density of CPnBs agree well with those found for the composites containing related but simpler molecules.
Core–shell nanoparticles (CSNPs) have become indispensable in various industrial applications. However, their real internal structure usually deviates from an ideal core–shell structure. To control how the particles perform with regard to their specific applications, characterization techniques are required that can distinguish an ideal from a nonideal morphology. In this work, we investigated poly(tetrafluoroethylene)–poly(methyl methacrylate) (PTFE–PMMA) and poly(tetrafluoroethylene)–polystyrene (PTFE–PS) polymer CSNPs with a constant core diameter (45 nm) but varying shell thicknesses (4–50 nm). As confirmed by transmission scanning electron microscopy (T-SEM), the shell completely covers the core for the PTFE–PMMA nanoparticles, while the encapsulation of the core by the shell material is incomplete for the PTFE–PS nanoparticles. X-ray photoelectron spectroscopy (XPS) was applied to determine the shell thickness of the nanoparticles. The software SESSA v2.0 was used to analyze the intensities of the elastic peaks, and the QUASES software package was employed to evaluate the shape of the inelastic background in the XPS survey spectra. For the first time, nanoparticle shell thicknesses are presented, which are exclusively based on the analysis of the XPS inelastic background. Furthermore, principal component analysis (PCA)-assisted time-of-flight secondary-ion mass spectrometry (ToF-SIMS) of the PTFE–PS nanoparticle sample set revealed a systematic variation among the samples and, thus, confirmed the incomplete encapsulation of the core by the shell material. As opposed to that, no variation is observed in the PCA score plots of the PTFE–PMMA nanoparticle sample set. Consequently, the complete coverage of the core by the shell material is proved by ToF-SIMS with a certainty that cannot be achieved by XPS and T-SEM.
A harmonization of sampling, sample preparation and detection is pivotal in order to obtain comparable data on microplastics (MP) in the environment. This paper develops and proposes a suitable sampling concept for waterbodies that considers different plastic specific properties and influencing factors in the environment.
Both artificial water including defined MP fractions and the discharge of a wastewater treatment plant were used to verify the derived sampling procedure, sample preparation and the subsequent analysis of MP using thermal extraction-desorption gas chromatography - mass spectrometry (TED-GC-MS).
A major finding of this paper is that an application of various particle size classes greatly improves the practical handling of the sampling equipment. Size classes also enable the TED-GC-MS to provide any data on the MP size distribution, a substantial sampling property affecting both the necessary sampling volume and the optimal sampling depth.
In the artificial water with defined MP fractions, the recovery rates ranged from 80 to 110%, depending on the different MP types and MP size classes. In the treated wastewater, we found both Polyethylene and polystyrene in different size classes and quantities.
Nanocomposites based on MgAL layered double hydroxides (LDH) and an epoxy resin were prepared and investigated by a combination of complementary methods. As epoxy resin Bisphenol A diglycidyl ether (DGEBA) was used with Diethylenetriamine as curing agent. The LDH was modified with taurine, which acts as an additional crosslinking agent due to its amine groups. The epoxy resin was cured in a presence of the nanofiller, which was added to the system in various concentrations. X-ray scattering, by combination of SAXS and WAXS was used to characterize the morphology of the obtained nanocomposites. These investigations show that the filler is distributed in the matrix as small stacks of ca. 10 layers. The molecular dynamics of the system, as probe for structure, was investigated by broadband dielectric spectroscopy. In addition to the - and -relaxation (dynamic glass transition), characteristic for the unfilled materials, a further process was found which was assigned to localized fluctuations of segments physically adsorbed or chemically bonded to the nanoparticles. The dielectric -relaxation is shifted to higher temperatures for the nanocomposites in comparison to the pure material but depends weakly on the content of nanoparticles. Further, for the first time Flash DSC was employed to a thermosetting system to investigate the glass transition behavior of the nanocomposites. The heating rates were converted in to relaxation rates. For low concentrations of the nanofiller the thermal data overlap more or less with that of the pure epoxy. For higher concentrations the thermal data are shifted significantly to higher temperatures. This is discussed in terms the cooperativity approach to the glass transition.
Dye activation of heterogeneous Copper(II)-Species for visible light driven hydrogen generation
(2019)
Heterogeneous Cu catalysts are widely used in photocatalytic hydrogen generation. The typical working mode includes the transfer of photo-induced charges from a semiconductor to CuO which itself is reduced to Cu2O to initiate the catalytic cycle. In this contribution a photosensitizer (dye), excited by visible light absorption, was used to transfer an electron to the CuO which after reduction catalyzes the water reduction to hydrogen. Several copper(II)-catalysts on high surface silica were prepared by impregnation or precipitation and applied in photocatalytic water reduction. The best catalyst CuO(Cl0.1)/SiO2, synthesized via incipient wetness impregnation of CuCl2 in MCM-41 and a following precipitation with NaOH, achieved a 6 times higher activity (1702 mmol h-1 g-1) compared to a previously investigated copper system (280 mmol h-1 g-1 for CuI) under the same reaction conditions. All materials were fully characterized by XRD, TEM and N2 sorption and further by magnetic resonance and X-ray methods EPR, ASAXS and XAS. In situ measurements evidenced a reduction of the initial Cu(II)-species, which confirms the (proposed) photocatalytic mechanism.
Polynuclear cationic aluminum hydroxide phases are known intermediates in the formation of aluminum oxides or (oxide) ydroxides upon hydrolysis of aluminum salt solutions. In the presence of sulfate anions, these aluminum polyoxocations (Al13) can form crystalline Al13 sulfates with varying chemical composition.
The formation of these Al13 sulfates in aqueous solution has been poorly understood. Here, we investigate the early stage crystallization of Al13 clusters in a sulfate-containing solution, in situ and in real time. Dynamics associated with Al13 sulfate formation have been obtained for the first time, using Synchrotron X-ray diffraction (XRD) of solutions suspended by acoustic levitation. Time-resolved in situ data show that the cubic phase, Na [(AlO4)Al12(OH)24(H2O)12](SO4)4*10H2O, forms after only minutes. The Formation mechanism of Al13 sulfates was found to depend on the sulfate:aluminum (SO4:Al) ratio. Ex situ XRD of the product Al13 sulfates in solution shows that for SO4:Al ratio ≤ 1.5 two other crystalline phases form, and convert to the cubic phase upon washing and drying. In situ XRD for the same ratio shows transient formation of an intermediate during the crystallization process.
Polymers of Intrinsic Microporosity (PIMs) of high performance have developed as materials with a wide application range in gas separation and other energy-related fields. Further optimization and long-term behavior of devices with PIMs require an understanding of the structure-property relationships including physical aging. In this context the glass transi-tion plays a central role, but with conventional thermal analysis a glass transition is usually not detectable for PIMs be-fore their thermal decomposition. Fast scanning calorimetry provides evidence of the glass transition for a series of PIMs, as the time scales responsible for thermal degradation and for the glass transition are decoupled by employing ultrafast heating rates of tens of thousands K s-1. The investigated PIMs were chosen considering the chain rigidity. The estimated glass transition temperatures follow the order of the rigidity of the backbone of the PIMs.
The authors describe and interpret curvature-related changes to the ellipsometric readout. As model system for a concave curvature, a set of three spherical microscopic indents in silicon (100) of different sizes was prepared by instrumented indentation testing using a spherical indenter. For reference, these samples were characterized by AFM to reveal the topography of each structure. The concavelike indents were analyzed by Mueller-Matrix imaging ellipsometry to extract lateral intensity images of 12 elements of the Mueller-Matrix. As a result of the detailed analysis of the image elements m22, m23, and m14, it was possible to correlate intensity changes and symmetry properties to depolarization and cross polarization induced by the edge threshold and the curved surface of the indent.
Effect of different drying methods on nutrient quality of the yellow mealworm (Tenebrio molitor L.)
(2019)
Yellow mealworm (Tenebrio molitor L.) represents a sustainable source of proteins and fatty acids for feed and food. Industrial production of mealworms necessitates optimized processing techniques, where drying as the first postharvest procedure is of utmost importance for the quality of the final product. This study examines the nutritional quality of mealworm larvae processed by rack oven drying, vacuum drying or freeze drying, respectively. Proximate composition and fatty acid profile were comparable between the dried larvae. In contrast, larvae color impressions and volatile compound profiles were very much dependent on processing procedure. High-temperature rack oven drying caused pronounced darkening with rather low content of volatiles, pointing toward the progress of Maillard reaction. On the other hand, vacuum drying or freeze drying led to enrichment of volatile Maillard reaction and lipid oxidation intermediates, whose actual sensory relevance needs to be clarified in the future. Beyond sensory and visual importance drying intermediates have to be considered with regard to their metal ion chelating ability; in particular for essential trace elements such as Zn2+. This study found comparable total zinc contents for the differently dried mealworm samples. However, dried larvae, in particular after rack oven drying, had only low zinc accessibility, which was between 20% and 40%. Therefore, bioaccessibility rather than total zinc has to be considered when their contribution to meeting the nutritional requirements for zinc in humans and animals is evaluated.
High resolution analysis of corrosion processes on stainless steels is a challenging task. The application of local electrochemical techniques such as scanning electrochemical microscopy (SECM) has opened new possibilities for the detection of corrosion products and activity on metallic surfaces. However, due to its stochastic nature, the analysis of pitting corrosion requires being at the right place at the right time. Scanning over large areas at a high resolution not only leads to long scan durations but also leaves many short-lived processes undetected. In this paper we present the combined automated operation of SECM and wire multi-electrodes connected to a multi-electrode analyzer (MMA). The inter-electrode currents between 25 wire electrodes connected via zero resistance ammeters (ZRA) are measured by the MMA at open circuit potential (OCP) and the electrodes reporting anodic currents are detected automatically to be analyzed by means of SECM. The results demonstrate the successful application of this methodology for the detection of unstable and stable pitting processes on 304 stainless steel in a corrosive aqueous environment.
Pirfenidone is an important drug molecule used in the treatment of idiopathic lung fibrosis. Although approved by the USFDA in 2014, pirfenidone’s aqueous solubility is too high and must be mitigated by additives. In this work, the cocrystallization of pirfenidone is explored as an alternative approach to reducing its solubility. Herein, an anhydrous form of pirfenidone is reported, alongside its first two reported cocrystals. The new crystalline solids are thoroughly characterized by single crystal X-ray diffraction (SCXRD), powder X-ray diffraction analysis (PXRD), Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA).
Equilibrium solubility and intrinsic dissolution rates (IDR) are studied for the cocrystals and compared to that of the parent drug. Both cocrystal forms exhibit drastically lower aqueous solubility (by up to 90%) and dissolution rates, rationalized based on both lattice energy calculations and consideration of intermolecular interactions in the solid state. Furthermore, we compare the physicochemical properties of solution-based material with that of material produced mechanochemically. Importantly, no differences are observed between the two production methods. This work demonstrates the strength of crystal Engineering strategies to beneficially modify important pharmaceutical properties and highlights the potential of mechanochemistry to facilitate this in an environmentally benign way.
Knowledge of the compressional and thermal behaviour of metals and alloys is of a high fundamental and applied value. In this work, we studied the behaviour of Ir, Rh, and their fcc-structured alloys, Ir0.42Rh0.58 and Ir0.26Os0.05Pt0.31Rh0.23Ru0.15, up to 70 GPa using the diamond anvil cell technique with synchrotron X-ray diffraction. We found that all these materials are structurally stable upon room-temperature hydrostatic compression in the whole pressure interval, as well as upon heating to 2273 K both at ambient and high pressure. Rh, Ir0.42Rh0.58 and Ir0.26Os0.05Pt0.31Rh0.23Ru0.15 were investigated under static compression for the first time. According to our data, the compressibility of Ir, Rh, fcc–Ir0.42Rh0.58, and fcc Ir0.26Os0.05Pt0.31Rh0.23Ru0.15, can be described with the 3rd order Birch-Murnaghan equation of state with the following parameters: V0 = 14.14(6) Å3·atom−1, B0 = 341(10) GPa, and B0' = 4.7(3); V0 = 13.73(7) Å3·atom−1, B0 = 301(9) GPa, and B0' = 3.1(2); V0 = 13.90(8) Å3·atom−1, B0 = 317(17) GPa, and B0' = 6.0(5); V0 = 14.16(9) Å3·atom−1, B0 = 300(22) GPa, B0' = 6(1), where V0 is the unit cell volume, B0 and B0' – are the bulk modulus and its pressure derivative.
Here, we report on a first mechanochemical synthesis of ettringite, an important cement hydrate phase. The mineral compound ettringite ([Ca3Al(OH)6]2·(SO4)3·26H2O) occurs rarely in nature, but is common for cement-based materials. Ettringite has wide technical application in the ceramic and paper industry. However, its typical wet-chemical synthesis is cumbersome and produces waste water and CO2 emissions. Here, we investigate the first mechanochemical synthesis of ettringite for developing an easy and sustainable alternative for industrial application. The mechanosynthesis was monitored in situ by coupled synchrotron X-ray diffraction (XRD) and infrared thermography (IRT). The consumption of the reactants and the formation of the reaction product were monitored with time-resolved XRD. IRT showed the temperature increase based on the exothermic reaction. The reaction conversion was significantly improved changing the strategy of the mechanosynthesis from a one- to a two-step process. The latter included neat pregrinding of solid reactants followed by a delayed addition of the stoichiometric amount of water. Thus, an increase of reaction conversion from 34 to 94% of ettringite could be achieved.
Powdered activated carbon (PAC) for organic micro-pollutant (OMP) removal can be applied effectively on wastewater treatment plant (WWTP) effluents by using re-circulation schemes, accumulating the PAC in the system. This technique is complex because several factors are unknown: (i) the PAC concentration in the system, (ii) specific and average contact times of PAC particles, and (iii) PAC particle loadings with target compounds/competing water constituents. Thus, performance projections (e.g. in the lab) are very challenging. We sampled large-scale PAC plants with PAC sludge re-circulation on eight different WWTPs. The PAC plant-induced OMP removals were notably different, even when considering PAC concentrations in proportion to background organic sum parameters. The variability is likely caused by differing PAC products, varying water composition, differently effective plant/re-circulation operation, and variable biodegradation. Plant PAC samples and parts of the PAC plant influent samples were used in laboratory tests, applying multiples (0.5, 1, 2, 4) of the respective large-scale “fresh” PAC doses, and several fixed contact times (0.5, 1, 2, 4, 48 h). The aimwas to empirically identify suitable combinations of lab PAC dose (as multiples of the plant PAC dose) and contact time, which represent the PAC plant
performances in removing OMPs (for specific OMPs at single locations, and for averages of different OMPs at all locations). E.g., for five well adsorbing, little biodegradable OMPs, plant performances can be projected by using a lab PAC dose of twice the respective full-scale PAC dose and 4 h lab contact time (standard deviation of 13 %-points).