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Characterization of statistical EO-PO copolymers containing different end groups by UPLC/ESI-MS
(2016)
Commercial statistical ethylene oxide (EO) and propylene oxide (PO) copolymers of different monomer compositions and different average molar masses were studied by liquid chromatography under critical conditions (LCCC). Theoretical predictions of the existence of a critical adsorption point (CPA) for statistical copolymers with a given chemical and sequence distribution, could be studied and confirmed. An improved way to determine these critical conditions in a copolymer, alongside the inevitable chemical composition distribution (CCD), with the aid of mass spectrometric detection is described. Shift of the critical eluent composition with the monomer composition of the polymers could be observed. Due to the relatively low average molecular weight, broad molecular weight distribution (MWD) and the presumed existence of different end group functionalities as well as sequence distribution, gradient separation only by CCD was not possible. Therefore isocratic separations at the CPA of definite CCD’s were applied. Although the various present distributions partly superimposed the separation process the goal of separation by end group functionality could still be achieved on the basis of the additional dimension of ESI-MS. The existence of HO-H besides the desired AllylO-H end group functionalities could be confirmed and their amount could be estimated.
Materials that respond to the environment by changing their properties are critical for developing
autonomously adaptive systems. However, to reversibly influence a material's inherent characteristics, such as its ability to self-heal, from distance without continuously expending energy, remains a challenging task. Herein, we report on the modul at ion of imine exchange kinetics by light, manifested in a remote controllable dynamic covalent polymer network. Simple mixing of a commercially available amino-functionalized polysiloxane with small amounts of a photoswitchable diarylethene cross-linker, carrying two aldehyde groups, yields a rubbery material. Its viscoelastic and self-healing properties can be reversibly tuned with everyday light sources, such as sunlight. Our two-component system offers the unique advantage that self-healing takes place continuously without any additives at ambient conditions and is neither dependent on continuous illumination nor does it require recent damage. Overall, our approach allows for the local amplification of intrinsic material properties in a permanent yet reversible fashion. The availability of the inexpensive sta1ting materials on a multi-gram scale, the easy synthesis of the polymer network, and its convenient handling paired with high versatility make our Approach highly applicable to create custom-tailored adaptive materials.
Healable materials are able to repair inflicted damages, herin often applied: dynamic covalent polymer networks. We have shown in this study that light of different colors shift the Diels-Alder and retro Diels-Alder crosslinking and decrosslinking equilibrium. This effect was utilized for self-healing of a polymer film. Small-angle X-ray scattering was used to quantifiy the polymeric mesh size on a nanoscale.
Calcium cobaltite is a promising p-type oxide thermoelectric material for high temperature applications due to its high figure of merit between 600 °C and 900 °C in air. The solid-state-reaction is well known for large scale powder synthesis of functional materials. As a high temperature process, the powder synthesis consumes a lot of energy. In different studies, different synthesis conditions were used for the preparation of calcium cobaltite powder. This study showed that a higher energy input (elevated temperatures, longer dwell times, or repeated calcinations) during powder synthesis does not increase but decrease the Seebeck coefficient and the electrical conductivity. The same correlation was determined for the densification. As a higher energy input leads to a larger grain size and therefore to a reduced sinter activity, it can be concluded that the thermoelectric properties are correlated with the sinter activity of the powder. These results can be used to minimize the energy demand for the powder synthesis of Ca₃Co₄ O₉.
Multilayer carbon nanomembrances (CNMs) could pave the way for a new ultrathin functional conductive coatings with tunable electrical, optical, and chemical properties. Due to their molecular thickness, they can also be regarded as “interfaces without bulk” separating regions of different gaseous, liquid, or solid components and controlling the materials exchange between them, making them optimal materials for membranes applications. Furthermore, their physical and chemical properties depend strongly on their structure, molecular composition, and the surroundings of either sides, thus allowing for tailored properties. Here, nanolayers of Aromatic p-terphenylthiol (TPT) self-assembled into 2D carbon monolayers (thickness - 1.6 nm) were synthesized and further crosslinked by ion bombardment, forming CNMs. Here, though a recently developed multilayer nanosheets routine, stacks of 5, 10, 15 and 20 TPT sheets where transferred on top of each other forming a multilayered CNMs. However, this transfer routine could introduce some intrinsic defects to the sheets, which would alter the molecular composition and / or structure, thus consequently the CNMs properties. Therefore, it is essential to characterize defects in “pure” TPT nanomembranes, before tailoring the molecular compositions, e.g. adding functional groups. For this reason, broadband dielectric spectroscopy (BDS) was utilized to characterize any defects that could be rasied during preparation. Due the structure of pure TPT membranes, no dipole moment should exsist. However, the presence of other elements, e.g. water or sulphur, would result in a dipole moment that could be probed by BDS.
As a main result, for all different stacked-layer numbers, a clear relaxation process is seen, which moves to higher frequencies with increasing the temperature. The temperature dependence of the relaxation rate of this process is independent of film thickness and can be well described by a common VFT function, hence a corporative motion. This relaxation process was assigned to intrinisic defects in the membranes, introduced during preparation, which was further confimed by a detailed anaylsis of the dielectric strength. This is the first BDS measurment on TPT CNMs.
Many engineering structures are made of composite materials or metal foam. To simulate the deformational behaviour of these structures often requires a high number of discretisation elements. This in turn yields a very large system of linear
equations that are extremely time and memory consuming or practically impossible to solve. It is therefore desirable to find an approach to overcome this obstacle.
Many engineering structures are made of composite materials or metal foam. To simulate the deformational behaviour of these structures often requires a high number of discretisation elements. This in turn yields a very large system of linear equations that are extremely time and memory consuming or practically impossible to solve. It is therefore desirable to find an approach to overcome this obstacle.
In the presentation different zinc coatings are presented and investigated. Their naturally formed protective layers are electrochemically characterized and corrosion relevant values are determined by using a gel pad based on polysaccharide. The corrosion relevant values allow the differentiation of various zinc coating systems and can describe the current protective effect provided by the coating. It is shown that gel-type electrolytes influence protective layers and coatings considerably less than corresponding bulk electrolytes. From the results it is evident that gel-type electrolytes represent a viable and promising field in corrosion research.zeige mehr
Deuterium permeation and cracking in duplex steels as viewed by ToF-SIMS and HR-SEM with data fusion
(2016)
Better understanding of hydrogen assisted degradation and trapping mecha-nisms requires sufficient imaging techniques for respective hydrogen-microstructure interaction studies, in particular with multi-phase metallic micro-structures [1]. The present work is focusing on the elucidation of deuterium be-havior in two austenitic-ferritic duplex stainless steels (DSS) under the assumption that deuterium behaves in many ways similarly to hydrogen [2]. For case studies standard 2205 and lean 2101 DSSs were chosen due to the extensive use of these steels in industry [3]. The analyses were conducted by using a novel in-situ permeation and Time-of-Flight secondary ion mass spectrometry (ToF-SIMS) imaging technique or by ex-situ ToF-SIMS imaging following electrochemical charging experiments. Another pioneering procedure was data fusion (including chemometry) of results of powerful laterally resolved chemical analysis and high resolution structural characterization techniques .
Results for the ex-situ observations showed a different influence of deuterium loading on the two steel grades as well as different damage mechanisms in each phase. Formation of sub-surface blisters between the ferrite and austenite were obtained in both the standard and the lean DSS. In both steels, an increased deuterium concentration was observed around deformed regions such as cracks, confirming that they originate from the presence of deuterium [4]. The formation of parallel cracks was obtained only in the austenite within the standard duplex whereas in the lean duplex the highest intensity of deuterium was obtained in the austenite along the ferrite-austenite interphase.
In comparison, application of the novel in-situ permeation technique enabled to register and record the deuterium permeation through the material and the respective saturation sequence of the two phases as well as the interfaces. Faster diffusion of the deuterium was observed in the ferrite and a direct proof for deuterium enrichment at the austenite-ferrite interface has been given [1]. The integration of the specified techniques gives a better insight into the processes leading to hydrogen induced failure. These two experimental techniques provide very valuable tools for elucidation of respective metallurgical failure mechanisms that can be used for the validation of respective numerical models for hydrogen assisted cracking (HAC).
The chemical industry has expressed great interest in using polyethylene terephthalate (PET) as material for packagings for the transport of dangerous goods. Due to the high strength and stiffness of PET, the wall thickness and weight of packagings can be reduced. This is a relevant cost factor. PET is a semi-crystalline thermoplast which is produced by polycondensation of terephthalic acid and ethylene glycol.
According to the European dangerous goods regulations RID and ADR, samples of PET design types of packagings for dangerous goods must be pre-stored with the original filling good for six months at 23°C, before the design type tests can be carried out. For packagings made of polyethylene (PE) tests to prove the stress cracking resistance by using laboratory methods are possible to reduce time and costs. Therefore, standard liquids, simulating the different types of damaging effects on PE are defined in RID and ADR. However, there is no information and research available about the damaging mechanisms on PET in comparison to PE, especially regarding to stress cracking resistance and test methods.
The aim of this work is to compare the stress cracking resistance of PE and PET with the Full Notch Creep Test (FNCT), which was developed by chemical industry and is described in the standards EN ISO 16101 and EN 15507. It was investigated whether testing specimens made of PE and PET with a full coplanar notch around the middle of the specimens show weakening after the impact of a tensile force in a wetting solution (Lutensol® FSA 10) at 50°C in a test device on the basis of the FNCT.
The test results confirmed the suitability of the method for eight PE grades. Unfortunately, this method couldn’t be used for PET because the specimens broke during notching. In addition the molding of the sheets and the following temper process for twelve hours are very time-consuming, and the specimens broke during notching due to the high brittleness of PET.
Another possibility to provide evidence of stress cracking resistance of PE packagings is laid down in BAM’s Dangerous Goods Rule BAM-GGR 015. This test was carried out with PE and PET bottles to compare both materials. Therefore 1l test bottles were filled with a 5% wetting solution and mounted with a clamping tool for 28 days at 40°C. Tensile test specimens were cut out afterwards from the middle of the bottles in the deformed areas. Tensile strength and breaking elongation of PE specimens were determined in comparison to the PET specimens. The tensile properties of the PET specimens couldn’t be determined due to the strength and the stiffness of the material.
In conclusion the only way to provide information about the stress cracking resistance of PET was to perform stacking tests. 1l bottles made of PE and PET were filled with a 5% wetting solution and stored with a stacking load for 28 days at 40°C according to EN ISO 16495. Design types of PE and PET both passed the stacking tests.
Hydrogen-assisted cracking (HAC) represents a significant failure risk for (high strength) creep resistant low-alloyed steel components in fossil-fired power plant applications at temperatures of up to and above 200 °C. This particularly applies to respective start-up and shut-down processes associated with alternating service-conditions in terms of load flexible power plants. For quantitative determination of localized crack critical hydrogen concentrations, the temperature dependent hydrogen diffusion coefficients have to be determined as exactly as possible.
However, available literature provides a wide range of hydrogen diffusion coefficients for low alloyed steels with similar microstructures. Additionally, the available diffusion data seem not to be very reliable and their scatter increases with decreasing temperature. One reason is that the experimental boundary conditions can have a major impact on the determination of respective effective diffusion coefficients. Hence, the scope of this study is to evaluate the influence of the experimental boundary conditions on the derived diffusion coefficients. In addition, different methods for calculating diffusion coefficients are discussed. To elucidate such influences and to draw a line to practical application, the diffusion and trapping behavior in the creep resistant steel 7CrMoVTiB10 10 has been studied.
For such purpose, hydrogen charged specimens were isothermally degassed at different temperatures using carrier gas hot extraction (CGHE). Based on experimental data, a numerical model has been developed by which the hydrogen transport behavior and the respective hydrogen distribution during CGHE can be assessed.
It is demonstrated that the specimen heating rate has a large influence on the calculated diffusion coefficients under assumption of isothermal degassing which elsewhere has been underestimated in the assessment of diffusion data in creep-resistant steels. The numerical results suggest that calculation methods for diffusion coefficients are limited if compared to experimental results. It also turned out that the sample preparation time before CGHE can enormously influence determined diffusion coefficients. Consequently, non-homogeneous hydrogen concentration profiles have to be anticipated in the simulations to arrive at characteristic effusion curves consistent to respective CGHE experiments. In turn, validated diffusion coefficients are now available for the low-alloyed Cr-Mo-V steel, which can be helpful to calculate appropriate hydrogen removal heat treatment procedures.
A test campaign was launched to determine the mechanical properties of the HL-LHC 11 T Nb3Sn magnet components in order to accurately model the mechanical properties in Finite Element simulations that predict the stress and strain distribution in These magnets. Static and dynamic test methods have been applied for determining elastic materials behavior, and highly accurate Young’s moduli are obtained with the dynamic methods resonance and impulse excitation. These non-destructive methods also enable temperature dependent modulus measurements during in situ heat cycles.
Hydrogen-assisted cracking (HAC) represents a significant failure risk for (high strength) creep resistant low-alloyed steel components in fossil-fired power plant applications at temperatures of up to and above 200 °C. This particularly applies to respective start-up and shut-down processes associated with alternating service-conditions in terms of load flexible power plants. For quantitative determination of localized crack critical hydrogen concentrations, the temperature dependent hydrogen diffusion coefficients have to be determined as exactly as possible.
However, available literature provides a wide range of hydrogen diffusion coefficients for low alloyed steels with similar microstructures. Additionally, the available diffusion data seem not to be very reliable and their scatter increases with decreasing temperature. One reason is that the experimental boundary conditions can have a major impact on the determination of respective effective diffusion coefficients. Hence, the scope of this study is to evaluate the influence of the experimental boundary conditions on the derived diffusion coefficients. In addition, different methods for calculating diffusion coefficients are discussed. To elucidate such influences and to draw a line to practical application, the diffusion and trapping behavior in the creep resistant steel 7CrMoVTiB10 10 has been studied.
For such purpose, hydrogen charged specimens were isothermally degassed at different temperatures using carrier gas hot extraction (CGHE). Based on experimental data, a numerical model has been developed by which the hydrogen transport behavior and the respective hydrogen distribution during CGHE can be assessed.
It is demonstrated that the specimen heating rate has a large influence on the calculated diffusion coefficients under assumption of isothermal degassing which elsewhere has been underestimated in the assessment of diffusion data in creep-resistant steels. The numerical results suggest that calculation methods for diffusion coefficients are limited if compared to experimental results. It also turned out that the sample preparation time before CGHE can enormously influence determined diffusion coefficients. Consequently, non-homogeneous hydrogen concentration profiles have to be anticipated in the simulations to arrive at characteristic effusion curves consistent to respective CGHE experiments. In turn, validated diffusion coefficients are now available for the low-alloyed Cr-Mo-V steel which might be helpful to calculate appropriate hydrogen removal heat treatment procedures, for instance.
Modeling of Hydrogen-Assisted Cracking (HAC) in Duplex Stainless Steels (DSS):
- Hydrogen causes significant degradation in DSS and consequently HAC
- Mechanisms of HAC have not been fully understood in two-phase microstructures
- Mesoscale numerical modeling for HAC in DSS was created, coupled to the macroscale, enabling simulation of HAC in both phases independent from predefined crack paths
Renewable resources become more and more relevant to maintain energy demands for an increasing global population. Biosynthetic fuels like biodiesel might replace conventional petrochemical fuels, such as diesel. However, more research is needed to characterize the interaction between the different fuels and the polymeric material, especially with respect to ageing and degradation.
The poster will present several interaction and degradation phenomena of high density polyethylene (PE-HD) induced by diesel and biodiesel 1-3. Also the possible influence of microbial growth (fungi and bacteria) is considered. The chosen PE-HDs are typical thermoplastic resins for container and storage tank applications. Degradation of PE-HD will be investigated by changes of the mechanical properties – with main emphasis on the Charpy impact strength 2. Furthermore, with alternating sorption and desorption cycles in combination with oven ageing the co-oxidation 3 of PE-HD in contact with biodiesel will be addressed.
The widespread use of antibiotics in livestock farming leads to trace residues in food products and wastewater, potentially entailing antimicrobial resistance in food-borne pathogens. The determination of antibiotics in aqueous environments and foodstuff is thus of major concern.
Analytical assays based on molecularly imprinted polymers (MIPs) have emerged as a valuable tool in this field due to the low production costs, stability, format adaptability and the possibility to imprint and thus their ability to recognize a wide variety of target analytes. With regard to optical sensing technologies, however, MIPs have only been used in considerably few applications, especially in fluorescence sensors. This limitation is basically due to the fact that the incorporation of a fluorescently responding moiety into a polymer matrix is challenging. One way to overcome this limitation is to use tailor-made fluorescent indicator monomers for direct transfer of the binding event into an optical signal. If such a monomer is integrated into a thin MIP-shell on microspheres such core/shell particles can be readily used in advanced multiplexing sensory fiber-optic microarrays.
Here, we propose such a fiber-optic microarray based on fluorescent MIP microspheres for antibiotics. The binding behavior and the selectivity of a microarray using these MIP were examined and compared with a non-imprinted polymer (NIP) control, employing the target molecules and other structurally closely related antibiotics.
Metal reducing bacteria (MRB) are able to utilize various materials such as iron, uranium and manganese as well as many organic compounds as electron acceptors. This process leads to the conversion of Fe(III) containing passive film species to soluble Fe(II) oxides and hydroxides. The reduction process triggers the acceleration of general and local corrosion processes. Electron transfer mechanisms are not yet fully understood. In literature it has been controversially discussed to which extend secreted electron shuttles contribute to the extracellular electron transfer (EET).
To understand the chemical and electrochemical interaction mechanisms of MRB with steel surfaces this project combines a variety of in-situ techniques. The changes in oxide chemistry on Fe/steel surfaces in the presence of biomolecules and MRB are under investigation using a newly designed electrochemical cell for in situ XANES (x-ray absorption near edge structure) spectroscopy. Electrochemical quartz crystal microbalance (eQCM) studies support the spectroscopic investigations to gain information about the kinetics of attachment processes and changes in biofilm viscosity. The biofilm structure and composition as well as cell viability are investigated by complementary ex situ spectroscopic and microscopic analysis.
Combining spectroscopic techniques and eQCM data with electrochemical measurements, biological processes and the resulting degradation of steel surfaces can be observed in a non-destructive manner. Selecting model systems and a defined biological medium allows the determination of individual effects of diverse surface and environmental parameters. The fundamental understanding of bacterial attachment mechanisms and initial steps of biofilm formation will contribute to the development of new antifouling strategies.
In recent years, upconversion nanocrystals (UCNC) have shown great promise for biological and medical applications, mainly because of their excitation in the NIR region, which provides minimum fluorescence background and a rather deep penetration into biological samples, as opposed to excitation in the visible or UV region. Moreover, they show a multitude of characteristic narrow emission bands as basis for ratiometric measurements. Commonly, Yb is the sensitizer of choice, because of a comparatively high absorption cross section, simple energy scheme, and rather efficient energy transfer to the activator, mostly Er, Tm or Ho. A main disadvantage of the use of Yb as sensitizer for biological and medical applications is its absorption band at 976 nm and hence the use of an excitation wavelength at which water has a non-negligible absorption. This can lead to significant sample heating, especially at long illumination times or high excitation power densities, and thus, tissue damage or even cell death. A possible solution is the tri-doping of UCNC with Nd as sensitizer, which can be excited efficiently at around 800 nm, where water absorption is at minimum.
The use of Nd as a sensitizer and Yb as a bridge between Nd and the activator Er in NaYF₄ nanocrystals is a relatively new way to overcome the problems of heating of samples in an aqueous environment. Disadvantages can arise from the tri-doping, which can favor non-radiative relaxation due to the more complicated excitation process compared to e.g., simple Yb,Er-doped UCNC, which might lower the upconversion quantum yields in these tri-doped systems. In order to quantify clear advantages, NaYF₄:Yb,Er,Nd nanoparticles were synthesized and spectroscopically studied using an 8 W 804 nm laser diode and a custom-designed Edinburgh instruments FSP980 spectrometer. Wavelength-dependent studies of the emission intensities and the decay kinetics of these tri-doped UCNC at different excitation power densities and excitation pulse widths revealed the clear advantages of preventing water absorption on measurable luminescence signals.
We were able to show the influence of pulse width and excitation power density on the luminescence intensities and decay kinetics lifetimes at different emission wavelengths. Additionally, we can clearly discern power density-dependent and independent peaks in the emission spectra. In summary, we demonstrate that the tri-doping of NaYF₄:Yb,Er,Nd nanoparticles is a very promising approach to render UCNC more efficient and to make them better suitable for biological and medical applications requiring measurements in aqueous environment.