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Photoelectron spectroscopy
(2018)
During the past few years significantly increasing research activities in the field of laser-induced periodic surface structures (LIPSS, ripples) have been reported since the generation of LIPSS in a single-step process provides a simple way of surface nanostructuring towards a control of optical, mechanical or chemical surface properties. In this contribution the current research state in this field is reviewed. The formation of LIPSS upon irradiation of metals, semiconductors and dielectrics by multiple linearly polarized Ti:sapphire fs-laser pulses (30-150 fs) is studied experimentally and theoretically. Different types of LIPSS with periods even below 100 nm can be generated. Their dynamics and formation mechanisms are analyzed and identified in ultrafast optical experiments. Complementing theoretical calculations of the laser-induced carrier dynamics address transient changes of the optical properties of the irradiated materials and reveal the importance of surface plasmon polaritons in the early stage of LIPSS formation. Various applications of these nanostructures are outlined.
One of the holy grails in chemistry is to reconstruct some of life’s functions with synthetic materials. In this contribution, we demonstrate that “simple” macromolecular architectures such as dendritic amphiphiles, Janus dendrimers, thermoresponsive and hybrid organic-inorganic (co)polymers enable to mimic some of the functions of proteins for biomineralization, natural bactericides, biological membranes or the stimuli-responsive cytoskeleton.
UCST-type thermoresponsive polymers (i.e. that phase separate from solution upon cooling) present a tremendous potential not only in aqueous media where they can be used in drug delivery, diagnostic and microfluidic applications, but also in water/alcohol mixtures, where they can be used for instance in sensing systems for alcohol-soluble drugs. However, only a few thermoresponsive polymers have been reported that present an UCST in a relevant temperature range and “green” solvents such as water or ethanol.
In this context, acrylamide-based monomers can be very useful building blocks for designing novel non-ionic UCST-type polymers because of their hydrophilic nature (with the appropriate side chain) and propensity to form hydrogen bonds. We will present our latest results on the UCST-type thermoresponsive behaviour of acrylamide- and 2,6-diaminopyridine-based homopolymers and copolymers in water or water/alcohol mixtures, and give some insights about the rational design of UCST polymers relying on H-bonding.
The paper addresses “WHITE LIGHT INTERFERENCE MICROSCOPY, ELLIPSOMETRY, AND INSTRUMENTED INDENTATION TESTING AS REFERENCE PROCEDURES“ and is subdivided in the following sections: 1. Measurement vs. testing vs. reference procedures, 2. White light interference microscopy (WLIM) for determination of step height h, 3. Spectroscopic ellipsometry (SE) for determination of layer thickness d and 4. Instrumented indentation testing (IIT) for determination of indentation hardness HIT. The following points are discussed in more detail: methodology of measurement and testing, uncertainty budgets for direct (WLIM), model-based (SE) and formula-based (IIT) reference procedures by means of specific examples. It is shown that standardization efforts are connected to reference procedures.
The wear rates of self-amted alumina couples show that friction as well as wear is largely determined by the above mentioned hydro-thermal conditions. The presence of water and ist amount available in the surrounding system either in liquid or in gaseous from plays a key role for friction and wear behavior and cabe benefical for the tribological profile of steam degradation resistant materials. Hot steam enhances the tribo-chemical formations of oxides and hydroxides on MgO-ZrO2, alumina and antimony impregnated carbon.
We will report on a new kind of ring-expansion polymerization (REP) of cyclic esters based of three classes of catalysts.
In contrast to REP described previously these new polymerizations are characterized by a self-extrusion of the catalysts resulting in cyclic homopolyesters as the only reaction product. These REP of L-lactide were performed in bulk at temperatures between 100 and 180°C without racemization. A simplified scheme of a REP catalyzed by BuCa or SnBi is presented below. With meso-lactide temperatures down to 60°C were realized. Depending on catalyst, time and temperature with equal quantities of even and odd-numbered cycles a strong predominance of either even or odd-numbered cycles was found.
The EC Recommendation on the definition of nanomaterial1, based solely on size of the constituent particles, foresees development of harmonised measurement methods ensuring ‘consistent results across materials and over time’. The EU/FP7 large research project NanoDefine (http://www.nanodefine.eu) has been exclusively dedicated to support the implementation of this EC Recommendation for the European Union’s legislation. For the first time, measurement techniques able to determine the size of nanoparticles have been evaluated systematically on a well-defined set of quality control materials (spherical, monodisperse) as well as industrial materials of complex shapes and considerable polydispersity. Particularly based on the analytical performance of the measurement techniques as tested on the challenging real-world particulate materials, it was possible to formulate recommendations for use of a new tiered approach consisting of screening and confirmatory techniques. Thus, a consistent framework of guidance for nanomaterial identification according to the EC Definition has been issued in form of the NanoDefiner e-tool (https://labs.inf.fh-dortmund.de/NanoDefiner), with a transparent decision flow scheme and an extensive user manual. Selected examples of analysis and classification as nano-/non-nanomaterials will be given, highlighting the limits of applicability of the available measurement techniques in dependence on sample properties. On some recent relevant developments in sample preparation – as a crucial part for an accurate analysis - will be also reported.
Universität Berlin Radiation damage to biomolecules such as DNA, is the reason to treat cancer via radiation therapy. The understanding of the molecular processes and the quantification of the underlying damaging mechanisms is necessary to develope more efficient irradiation protocols for cancer therapy. Thereby damage to DNA is of key interest due to its central role in reproduction and mutation. Due to the high amount of water in biological tissue, most of the damage is caused by the secondary particles which are produced by the interaction of ionizing radiation with water. Thereby a multitude of species are produced, e.g. kinetic low energy electrons, prehydrated electrons, OH-radicals and ions. The quantification of the contribution to DNA damage by the various species is of interest. Here we present an experimental approach to disentangle their relative DNA strand break yields. Plasmid DNA (pUC19 ) is irradiated in water with electrons under the presence of different scavengers. The presented preliminary results reveal the relative contributions of OH-radicals, low energy electrons and prehydrated electrons and their DNA single and double strand break yields.
The XPS information depth of approximately 10 nm is in the same size range as the outer membrane of the gram-negative bacteria, which makes XPS a suitable tool for determining the elemental composition of the bacterial surface and monitor changes caused by outer stress like dehydration or exposure to antimicrobials. However, bacteria are inherently in a hydrated state, and therefore only compatible to ultra-high vacuum after extensive sample preparation, which may degrade the sample constituents. This issue is addressed by the development of near-ambient pressure (NAP)-XPS, which enables bacteria and biofilms to be characterised in their native wet state. Artificial biofilms, bacteria and biofilms of Escherichia coli have been characterised with the laboratory NAP-XPS instrument EnviroESCA from SPECS GmbH, at pressures ranging from high vacuum to 12 mbar, and in both humid and dry environment. By studying biological samples in their native wet state, new insight about composition and transport of drugs through cell membranes and the extracellular polymeric substance (EPS) of biofilms can be obtained. In this contribution, the latest progress on biofilm characterisation by NAP-XPS will be presented, and measurement capabilities and limitations will be discussed.
For the first time, the molecular mobility of two linear-shaped tetramethylated guanidinium triflates ionic liquid crystals (ILCs) having different length of alkyl chains was investigated by a combination of broadband dielectric spectroscopy (BDS) and specific heat spectroscopy (SHS). SHS was carried out by differential AC-chip calorimetry at higher frequencies and temperature modulated DSC at lower frequencies. These ILCs can form a hexagonal ordered columnar mesophase. Two relaxation processes were found by BDS for both samples. At low temperatures, a γ-processes is observed which is assigned to specific localized fluctuations. At higher temperatures, α1-processes take place. α2 processes were also detected by SHS but with a completely different temperature dependence of the relaxation times. Different molecular assignments of α1- and α2-processes are suggested. At even higher temperatures, conductivity was detected by BDS.
Hyperbranched PAMAM/ Kaolinite Nanocomposites: Decoupling phenomenon and conductivity mechanism
(2018)
Increasing demands of the daily life requires a continuous discovering of new and tailored properties of materials that can be utilized in covering the requirements in several fields. Hyperbranched polymers (HBPs) are macromolecules that are characterized by a highly branched structure and multiplicity of reactive end groups, which could be promising for numerous applications. Here, hyperbranched poly(amidoamine) (HPAMAM)/ Ka nanocomposites was prepared via an in-situ polymerization and an ex-situ method. The latter approach leads to a partly intercalated structure of the nanocomposites, while the former method results in an exfoliated morphology. Α combination of different techniques such as broadband dielectric spectroscopy (DBS), SXAS, FTIR, TEM, and DSC are employed to study the prepared samples. For the HPAMAM/ Ka-DCA nanocomposites (an ex-situ samples), the results indicated that the dc conductivity is increased by 4 orders of magnitude, with increasing concentration of the Ka-DCA. As an interesting result is that a significant decoupling between the characteristic time for conductivity relaxation and the segmental dynamics was observed, which depends on the concentration of the nanofiller. For the HPAMAM/ EDA nanocomposites (an in-situ polymerization), the dc conductivity is also increased with increasing the concentration of the Ka-EDA. The decoupling phenomenon and conductivity mechanism are discussed in detail.
UCST-type thermoresponsive polymers (i.e. that phase separate from solution upon cooling) present a tremendous potential not only in aqueous media where they can be used in drug delivery, diagnostic and microfluidic applications, but also in water/alcohol mixtures, where they can be used for instance in sensing systems for alcohol-soluble drugs. However, only a few thermoresponsive polymers have been reported that present an UCST in a relevant temperature range and “green” solvents such as water or ethanol.
In this context, acrylamide-based monomers can be very useful building blocks for designing novel non-ionic UCST-type polymers because of their hydrophilic nature (with the appropriate side chain) and propensity to form hydrogen bonds. We will present our latest results on the UCST-type thermoresponsive behaviour of acrylamide- and 2,6-diaminopyridine-based homopolymers and copolymers in water or water/alcohol mixtures, and give some insights about the rational design of UCST polymers relying on H-bonding.
Imaging of surfaces regarding topographical, morphological, micro-structural, and chemical features is a key requirement for quality control for the identification of contaminated, degraded, damaged or deliberately modified surface areas vs. clean, virgin, undamaged or unmodified regions. As optical functions may represent any of these changes on the micro- and nano-scale, imaging ellipsometry (IE) is the technique of choice using either intensity, phase, or/and amplitude contrast for visualization of low-contrast surface modifications [1, 2]. Defects or surface and film features whether native or artificial, intended or unintended, avoidable or unavoidable as well as surface pattern are of interest for quality control. In contrast to microscopic techniques operated at normal incidence, ellipsometry as oblique-incidence technique provides improved contrast for vertically nano-scaled add-on or sub-off features such as ultra-thin transparent films, metallic island films, carbon-based thin films, laser modification or laser induced damage, dried stain, cleaning agent or polymeric residue. Two-sample reference techniques, i.e. referenced spectroscopic ellipsometry (RSE) may further increase sensitivity and decrease measurement time. In case of particulate accumulations depolarization contrast imaging (DCI) may improve the lateral resolution beyond the Abbe limit. This has been proven for silica spheres as reference in terms of single particles, particulate accumulations or particulate monolayers and layer stacks. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used for reference measurements of particle diameter, particle height, or particulate layer/accumulation thickness. It has been shown that single silica particles of 250 nm in diameter, i.e. at least a factor of 4 better than the lateral resolution limit as of now, can be visualized on even substrates. However, the ellipsometric measurement of particle diameters of this size needs further efforts interpretation.
Ultrashort laser pulse micromachining features a high precision. By increasing the repetition rate of the applied laser to several 100 kHz, laser processing becomes quick and cost-effective and make this method attractive for industrial applications. Upon exceeding a critical laser intensity, hard X-ray radiation is generated as a side effect. Even if the emitted X-ray dose per pulse is low, the accumulated X-ray dose becomes significant for high-repetition-rate laser systems so that radiation safety must be considered. The X-ray emission during ultrashort laser processing was investigated for an intensity range up to 2.6*10^14 W/cm2. The investigations were performed with a laser emitting pulses with 925 fs pulse duration, at 1030 nm wavelength and 400 kHz repetition rate. Steel, tungsten, and glass were studied in ambient air. Corresponding X-ray spectra and X-ray dose measurements were presented. Suitable radiation protection strategies were shown.
The molecular dynamics and ionic conductivity of ionic liquid crystals (ILCs) forming a columnar mesophase, two linear-shaped tetramethylated guanidinium triflates ILCs having different lengths of alkyl chains, were investigated by a combination of Broadband Dielectric Spectroscopy (BDS) and Specific Heat Spectroscopy (SHS). Three processes were detected by BDS; at low temperature γ-process, at higher temperatures α-process and at even higher temperatures conductivity. The γ-process indicates localized fluctuations, and the α-process designates cooperative fluctuations. Slightly different restrictions were found for conductivity processes of LC536 and LC537 due to the slightly different lengths of alky chains. The conductivity mechanisms in the plastic crystalline and the columnar mesophase have been revealed by BDS and different charge carriers were assigned for the different phases. Furthermore, the cooperative dynamics were also probed by SHS. The cooperative dynamics probed by the different techniques (BDS and SHS) compared, and assigned to the different restrictions on the cooperativity due to the difference in the sensitivity of the techniques.
Ultrashort laser pulse micromachining features a high precision. By increasing the repetition rate of the applied laser to several 100 kHz, laser processing becomes quick and cost-effective and make this method attractive for industrial applications. Upon exceeding a critical laser intensity, hard X-ray radiation is generated as a side effect. Even if the emitted X-ray dose per pulse is low, the accumulated X-ray dose becomes significant for high-repetition-rate laser systems so that radiation safety must be considered.
UCST-type thermoresponsive polymers (i.e. that phase separate from solution upon cooling) present a tremendous potential not only in aqueous media where they can be used in drug delivery, diagnostic and microfluidic applications, but also in water/alcohol mixtures, where they can be used for instance in sensing systems for alcohol-soluble drugs. However, only a few thermoresponsive polymers have been reported that present an UCST in a relevant temperature range and “green” solvents such as water or ethanol.
In this context, acrylamide-based monomers can be very useful building blocks for designing novel non-ionic UCST-type polymers because of their hydrophilic nature (with the appropriate side chain) and propensity to form hydrogen bonds. We will present our latest results on the UCST-type thermoresponsive behaviour of acrylamide- and/or 2,6-diaminopyridine-based homopolymers and copolymers in water or water/alcohol mixtures, and give some insights about the rational design of UCST polymers relying on H-bonding.
A presentation held for the seminar "Ausgewählte analytische Methoden der Physik" hosted by Prof. Birgit Kanngießer at TU Berlin. The first part focus on depth-dependent XPS-measurements (XPS, synchrotron HAXPES) to obtain a concentration profile of iodine in an artificial biofilm. In the second part, NAP-XPS measurements of various bacterial samples are presented.
The application of PVD-coatings ranges from mechanical engineering, i.e. thicker tribological coatings, to precision optics, i.e. thinner optical coatings. For physical vapor deposition (PVD) technologies such as evaporation, sputtering, ion beam assisted/driven deposition, vacuum is a prerequisite for two reasons: at first process-related ones (evaporation source, plasma discharge, and mean free path) and at second coating-related ones (pure, perfect, and dense films). Usually, the goal is a homogenous coating of defined stoichiometry and micro-structure without any imperfection.
However, the implementation of micro- or nano-particles may occur accidentally or delibe-rately. Independent of the particle origin, there are two fundamental rules regarding coating functionality: at first, the larger the particle diameter to coating thickness ratio the more affected the functionality of the coating, and at second, the larger the material contrast in terms of the functional feature of interest the more affected the coating performance. Hence, embedded particles have to be avoided for the majority of thin films by all means. The unintended implementation of particles usually results in a malfunction of the coating from the beginning or is at least considered as a weak point of the coating creating a time-dependent defect under service conditions. The intended implementation of particles on surfaces and in coatings may create add-on features, topographic ones and functional ones, however, the facts mentioned hold true.
Examples of particle-initiated coating defects are demonstrated in dependence on the origin and the field of application. Strategies for deliberate attachment/embedding of particles on surfaces/in coatings are discussed regarding process compatibility and coating integrity. For industrial applications, both the validation of process compatibility of particle injection and the plasma resistance of particles under vacuum and plasma conditions have to be confirmed. Further points of interest are the homogeneity of particle distribution and the avoidance of particle agglomeration which is still a crucial point for dry dispersed particles. So far, technical applications are limited to PVD hybrid coatings, plasma dispersion coatings are still a challenge except for applications where homogeneity is not required as in case of product authentication.
Multi-functional coatings are a key requirement for surface engineering. General demands are adhesion and long-term stability under service conditions. The modification of surfaces by means of PVD-, ECD- or hybrid processes allows an add-on functionalization of surfaces by a huge diversity of materials with both lateral and vertical micro-/nano-designs. This fact is a prerequisite for micro- and sensor-systems in lab-on-chip and sensor-on-chip technology. Two layer-based sensor principles are presented, i.e. surface plasmon resonance enhanced spectroscopic ellipsometry (SPREE) for detection of hazardous gases and magneto-optical sensors on smart-coated fiber Bragg gratings (FBG) for structural health monitoring (SHM).
The interdependence of substrate features, coating properties, and layer design is discussed firstly for gas sensitivity and selectivity of SPREE-sensors and secondly for sensitivity and selectivity of magneto-strictive coatings to mechanical strain or external magnetic fields resulting in an optical displacement of the Bragg wavelength of FBG-sensors. Moreover, generic features such long-term stability, crucial process-related fabrication conditions, and effects of operational and environmental parameters are discussed with respect to the sensor performance. It has been shown that appropriate layer design and adapted selection of layer materials (SnOx/Au, Fe/Ni:SnOx/Au; Ni/NiFe-Cu-Cr) result in improved sensor parameters and may enable new sensor applications.
Extraction of true, 3D shape (and size) of non-spherical nanoparticles (NPs) is associated with errors by conventional 2D electron microscopy using projection images. Significant efforts within the ISO technical committee TC 229 ‘Nanotechnologies’ are aimed at establishing accurate TEM and SEM measurement of NP size and shape as robust, standard procedures. Study groups have been organizing inter-laboratory comparisons on well-selected NP systems according to the market needs, such as aggregated titania nano-powder for which size and shape distribution of primary crystallites of irregular shape must be measured accurately. To be noticed is e. g. the fact that the measurement procedure allows only manual selection of the particles clearly distinguishable for analysis as well as manual definition of the contour of the imaged NPs.
An inter-laboratory exercise on titania NPs (pure anatase, grown by hydrothermal synthesis) of well-defined non-spherical shape, i.e. bipyramidal has been recently started within ISO/TC 229 under similar conditions as for the irregular shaped titania. Overlapped particles were allowed to be considered, as long as they are clearly distinguishable. One decisive NP selection criterion was to analyze only those NPs with a roundness value below 0.7, i.e. the NPs laying on the support foil and, hence, with projection areas clearly deviating from perfect circles (R=1). The overall evaluation (for 15 labs) of the size descriptors (area, Feret, minFeret, perimeter) and shape descriptors (aspect ratio, roundness, compactness, extent) by analysis of variance is just to be finished and included in ISO/WD 21363 Nanotechnologies -- Protocol for particle size distribution by transmission electron microscopy.
Following the 2017 meeting, progress with the Key Comparison CCQM-K153 related to the BET specific surface lead by UNIIM and the Pilot Study P-190 “Thickness Measurement of nm HfO2 Films” lead by KRISS will be discussed.
The 16th meeting of SAWG will focus on
•survey on CMC claims submitted with reference to K-129 and K-136.
•the overall and SAWG specific aspects of the CCQM Strategy process,
•a consideration of comparisons on convention methods as recommended by the CCQM Plenary Meeting 2017,
•the 2019 CCQM Workshop and paper(s) for Metrologia’s Special Issue,
•discussion of future comparisons.
Dielectric spectroscopy (BDS) was employed to investigate the dynamics of thin films (7 – 200 nm) of a Poly (vinyl methyl ether) (PVME) / Polystyrene (PS) blend (50:50 wt%). For the BDS measurements Nano-Structured Capacitors (NSC) were employed, where films have a free surface. This method was applied for film thicknesses up to 36 nm. Thicker films were prepared between Crossed Electrodes Capacitors (CEC). The spectra of the films showed multiple processes. The first process was assigned to the -relaxation of a bulk-like layer. For films measured by NSC, its rates were higher compared to that of the bulk blend. This behavior was related to a PVME-rich free-surface layer. A second process was observed for films measured by CEC (process X) and the 36 nm film measured by NSC (process X2). This process was assigned to fluctuations of PVME constraint by PS. Its activation energy was found to be thickness dependent, due to the evidenced thickness dependency of the compositional heterogeneity. Finally, a third process with an activated temperature-dependence was observed for all films measured by NSC (process X1). It resembled the molecular fluctuations in an adsorbed layer found for films of pure PVME.
Vesicles self-assembled in water from natural and synthetic phospholipids (liposomes), amphiphilic block copolymers (polymersomes), and more recently amphiphilic Janus dendrimers (dendrimersomes) -5 as hollow soft structures in the nano size regime have attracted increasing interest as they can mimic primitive and contemporary biological membranes, and can be configured into biomimetic nanocapsules with application in nanomedicine such as gene, proteins and drug carriers or theranostics.
Compared to other amphiphilic structures, the molecular structure of Janus dendrimers can be precisely controlled: by using the vast range of tools from organic chemistry their size, architecture, density, generation as well as the number of end groups of the individual dendrons can be modified as desired.
Unfortunately, the controlled production of supramolecular aggregates made thereof is still a challenging task. Conventional batch-based techniques such as the solvent injection method or the film hydration method typically go along with a lack of control over self assembly/mixing and thus over size, morphology and size distribution of the vesicles.
The micromixer technology is a promising method for the controlled preparation of supramolecular assemblies as it allows control of mixing at microscale level. In addition, such microfluidic systems benefit from a high mixing efficiency, a low mixing time as well as from a reproducible and continuous production of soft nanoparticles. Herein, we report on the microfluidic-controlled self-assembly of Janus dendrimers as dendrimersomes and the impact of the mixing parameters on the self-assembly process.
One of the holy grails in chemistry is to reconstitute some of life’s functions with or within synthetic materials. In this contribution, we demonstrate that “simple” macromolecular architectures such as dendritic amphiphiles, Janus dendrimers, thermoresponsive and hybrid organic-inorganic (co)polymers enable to mimic some of the functions of proteins for biomineralization, natural bactericides, biological membranes or the stimuli-responsive cytoskeleton.
In well-annealed thin polymer films, with non-repulsive polymer/substrate interactions, an irreversibly adsorbed layer is expected to form. These adsorbed layers have shown great potential for technological applications. However, their growth kinetics and molecular dynamics are still not fully understood. This is partially due to the hard accessibility of these layers in thin films. Here, the irreversibly adsorbed layers of homopolymer thin films are revealed by solvent-leaching experiments. First, the growth kinetics of these layers is investigated as a function of annealing times and original film thickness. The thickness, topography and quality of the adsorbed layer is controlled with Atomic Force Microscopy (AFM). Secondly, the molecular mobility of the adsorbed layer is investigated with Broadband Dielectric Spectroscopy (BDS). A recently developed nanostructured capacitor is employed to measure the adsorbed layers with a free surface layer. The results are quantitatively compared and discussed with respect to recently published work.
The structure and molecular dynamics of thin polymer films are of topical interest of soft matter-physics. Commonly, spatial structural heterogeneities of 1D confined thin films (surface, bulk-like and adsorbed layer), are expected to alter the glassy dynamics, compared to the bulk. Here, Specific Heat Spectroscopy (SHS) was used, to investigate the glassy dynamics of thin films of an asymmetric miscible PVME/PS 25/75 wt% blend. SHS measurements showed a non-monotonous thickness dependence of the dynamic Tg, on the contrary to the previously investigated PVME/PS 50/50 wt%. For PVME/PS 25/75 wt% thin films (> 30 nm), due to the presence of PVME-rich adsorbed and surface layers, the bulk-like layer experienced a thickness dependent increase of PS concentration. This led to a systematic increase of dynamic Tg. Further decrease of the film thickness (< 30 nm), resulted in a decrease of dynamic Tg, ascribed to the influence of the surface layer, which has a high molecular mobility. This is the first study, which shows deviations of dynamic Tg of thin films, compared to the bulk, resulting from the counterbalance of the free surface and adsorbed layer.
Mixing and curing of geopolymers and related alkali-activated materials without storage and handling of highly alkaline solutions possesses advantages regarding safety and economic viability; one possible approach is to produce these materials from solid silica feedstocks and solid sodium aluminate, and subsequent mixing with water. We present a comparison between geopolymers and geopolymer-zeolite composites synthesized by this route from different silica feedstocks (by-product silica from chlorosilane production, microsilica, rice husk ash) and with different SiO2/Al2O3 ratios, using results from XRD, NMR, SEM, thermal analysis, mechanical and acid resistance testing. The use of rice husk ash favors formation of a fully amorphous geopolymer with high strength. Utilization of the other silica feedstocks leads to formation of geopolymer-zeolite composites, the amount and kind of zeolites depending on the feedstock and the SiO2/Al2O3 ratio. These composites show beneficial dehydration behavior, viz. no distinct dehydration step of thermal strain, with the phase assemblage after heating to 1000 °C controlled by the starting composition. Mortars produced from both, the geopolymers as well as the compo¬sites, exhibit high resistance to sulfuric acid attack, making them promising materials for the construction and the repair of industrial and sewer structures.
One of the holy grails in chemistry is to reconstruct some of life’s functions within synthetic materials. In this contribution, we demonstrate that “simple” macromolecular architectures such as dendritic amphiphiles, Janus dendrimers, thermoresponsive and hybrid organic-inorganic (co)polymers enable to mimic some of the functions of proteins for biomineralization, natural bactericides, biological membranes or the stimuli-responsive cytoskeleton.
From simple molar mass disperse homopolymers over copolymers to functionalized, 3-dimensional structures containing various distributions, the complexity of polymeric materials has become more and more sophisticated in recent years. With applications in medicine, pharmacy, smart materials or for the semiconductor industry the requirements for the characterization have risen with the complexity of the used polymers. For each additional distribution, an additional dimension in analysis is needed. Small, often isobaric heterogeneities in topology or microstructure can usually not be simply separated chromatographically or distinguished by any common detector. Instead of a complicated, time consuming and/or expensive 2d-chromatography or ion mobility spectrometry (IMS) method, that also has its limitations, here a simple approach using size exclusion chromatography (SEC) coupled with electrospray ionization mass spectrometry (ESI) is proposed. We used SEC for the separation because unlike other separation modes the separation in this mode solely should occur due to the hydrodynamic volume with no interference of other interactions. This simplifies the interpretation and the above mentioned heterogeneities should show a slight difference in hydrodynamic volume. ESI mass spectrometry can offer more than an access to mass dependent information like MMD, end group masses or CCD in polymer analysis. The online coupling to SEC allows the analysis of reconstructed ion chromatograms (RIC) of each degree of polymerization. While a complete separation often cannot be achieved, the derived retention times and peak widths lead to information on the existence and dispersity of heterogeneities in microstructure or topology, that are otherwise inaccessible or accessible only by time consuming or expensive methods. Because these heterogeneities might vary with the molar mass, analysis of the whole MMD-Peak (here the total ion current (TIC)) would not lead to the desired information. The broadening of the chromatographic peaks in this case does not origin from the already well known band broadening factors in chromatography from diffusion. This band broadening is attributed to the nature and composition of the analyte itself. Surprisingly there is very little investigation into the peak width or peak shape due to analyte structure itself found in literature. It is also shown, that with proper calibration even quantitative information could be obtained. This method is suitable to detect small differences in e. g. branching, topology, monomer sequence or tacticity and could potentially be used in production control of oligomeric products or other routinely done analyses to quickly indicate deviations from set parameters. Based on a variety of examples we demonstrate the possibilities and limitations of this approach.
The common characterization and identification of pollen is a time-consuming task that mainly relies on microscopic determination of the genus-specific pollen morphology. A variety of spectroscopic and spectrometric approaches have been proposed to develop a fast and reliable pollen identification using specific molecular information. Amongst them, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) shows a high potential for the successful investigation of such complex biological samples. Based on optimized MALDI sample preparation using conductive carbon tape, the application of multivariate statistics (e.g. principal components analysis, PCA) yields an enormous improvement concerning taxonomic classification of pollen species compared to common microscopic techniques.
Since multivariate evaluation of the recorded mass spectra is of vital importance for classification, it’s helpful to implement the applied sequence of standard Matlab functions into a graphical user interface (GUI). In this presentation, a stand-alone application (GUI) is shown, which provides multiple functions to perform fast multivariate analysis on multiple datasets. The use of a GUI enables a first overview on the measured dataset, conducts spectral pretreatment and can give classification information based on HCA and PCA evaluation. Moreover, it can be used to improve fast spectral classification and supports the development of a simple routine method to identify pollen based on mass spectrometry.
Investigation of core-shell nanoparticles using scanning transmission x-ray microscopy (STXM)
(2018)
A scanning transmission x-ray microscopy (STXM) based methodology is introduced for determining the dimensions (shell thickness, core and total diameter) of core-shell nanoparticles which exhibit a strong x-ray absorption contrast and a well-defined interface between core and shell material. A low radiation dosage during data acquisition and, therefore, less x-ray beam induced damage of the sample is achieved by recording STXM images only at two predetermined energies of maximum absorption contrast, instead of recording a stack of images across the whole absorption edge. A model core-shell nanoparticle, polytetrafluoroethylene (PTFE) cores with polystyrene (PS) shell, is used for demonstration. Near edge x-ray absorption fine structure (NEXAFS) spectroscopy confirms the significant difference in x-ray absorption behavior between PTFE and PS. Additionally, due to the insolubility of styrene in PTFE a well-defined interface between particle core and shell is expected. In order to validate the STXM results, both the naked PTFE cores as well as the complete core-shell nanoparticles are examined by scanning electron microscopy (SEM). The introduced STXM based methodology yields particle dimensions in good agreement with the SEM results (deviation equal or less than 10%) and provides additional information such as the position of the particle core which cannot be extracted from a SEM micrograph.
In this presentation, we report on the Determination of the glass transition temperature of thin layers of Polyvinylmethylether (PVME) depending on the thickness of the polymer layer. The glass Transition of thin polymer layers is currently under much investigation due to the nano-confinement effects proposed to appear in dependence on the layer thicknesses in the nm range. The properties of the polymer, the temperature range, as well as the thicknesses range of the polymer layers pose a serious challenge to the investigation by means of
spectroscopic ellipsometry. By careful choice of experimental parameters, we were able to investigate the thickness change by temperature of PVME layers in the range between 2 and 300 nm and in the temperature range between 200 K and 340 K. By optimizing the analysis process, we were able to determine Tg values within this parameter range with sufficient accuracy to investigate the Tg change due to confinement effects.
Alongside the change of position of the glass transition with thickness, we discuss the details of the ellipsometric analysis and its implications for the resulting thermal properties of the thin polymer layers as well as the accuracy of the Tg value with respect to the method used in the analysis process.
Polymers with intrinsic microporosity are promising candidates for the active separation layer in gas separation membranes. Here, by means of inelastic neutron scattering, the vibrational density of states (VDOS) and the molecular mobility were investigated for PIM-1, the prototypical polymer with intrinsic microporosity. The results are compared to data measured for a more conventional high-performance polyimide used in gas separation membranes (Matrimid).
The measured data show the characteristic low frequency excess contribution to the VDOS above the Debye sound wave level, generally known as the Boson peak in glass-forming materials. In comparison to the Boson peak of Matrimid, that of PIM-1 is shifted to lower frequencies. This shift is discussed considering the microporous, sponge-like structure of PIM-1 as providing a higher compressibility at the molecular scale than for conventional polymers.
Elastic fixed window scans were measured on a neutron backscattering spectrometer to have an overview about the molecular dynamics at a time scale of ca. 1 ns. The temperature dependence of the estimated mean squared displacement shows a step-like increase in the temperature range from 100 K to 250 K indicating the onset of some molecular mobility. The nature of this motional process was analyzed in detail by quasielastic neutron scattering where the data are discussed with regard to both the q- and the temperature dependence.
A scanning transmission x-ray microscopy (STXM) based methodology is introduced for determining the dimensions (shell thickness, core and total diameter) of core-shell nanoparticles which exhibit a strong x-ray absorption contrast and a well-defined interface between core and shell material. A low radiation dosage during data acquisition and, therefore, less x-ray beam induced damage of the sample is achieved by recording STXM images only at two predetermined energies of maximum absorption contrast, instead of recording a stack of images across the whole absorption edge. A model core-shell nanoparticle, polytetrafluoroethylene (PTFE) cores with polystyrene (PS) shell, is used for demonstration. Near edge x-ray absorption fine structure (NEXAFS) spectroscopy confirms the significant difference in x-ray absorption behavior between PTFE and PS. Additionally, due to the insolubility of styrene in PTFE a well-defined interface between particle core and shell is expected. In order to validate the STXM results, both the naked PTFE cores as well as the complete core-shell nanoparticles are examined by scanning electron microscopy (SEM). The introduced STXM based methodology yields particle dimensions in agreement with the SEM results and provides additional information such as the position of the particle core which cannot be extracted from a SEM micrograph.
Solution doping of off-the-shelf plastic optical fibers (POFs) represents rather simple and cheap way for preparing custom cladding-doped POFs (CD-POFs) with short to medium lengths. CD-POFs are especially attractive for environmental sensing applications, but might be of interest for illumination task as well. In this work, the proposed doping technique is tested with three different commercial low-cost polymethyl methacrylate (PMMA) POFs; Eska CK-40 and Eska GK-40 from Mitsubishi Rayon and Raytela PGU-FB1000 from Toray. The aim of the work is to aid the selection of the most suitable fiber yielding highest optical quality of prepared CD-POFs. Firstly, the optimal doping times are determined for the individual fiber types using short fiber samples. Secondly, longer 10 m CD-POFs are prepared from all tested fibers using the optimized doping procedure. Finally, attenuation of pristine POFs and prepared CD-POFs is measured using optical time domain reflectometry in order to characterize the impacts of the doping on fiber optical properties. In addition, the importance of post-doping drying procedure for CD-POF optical performance is investigated as well. The results suggest that, although doping of all tested fibers is generally feasible, Eska CK-40 is the most suitable candidate with regard to the doping efficiency and fiber post-doping performance.
Interfaces provide the structural basis for function as, for example, encountered in nature in the membrane-embedded photosystem or in technology in solar cells. Synthetic functional multilayers of molecules cooperating in a coupled manner can be fabricated on surfaces through layer-by-layer self-assembly. Ordered arrays of stimuli-responsive rotaxanes undergoing well-controlled axle shuttling are excellent candidates for coupled mechanical motion. Such stimuli-responsive surfaces may help integrating synthetic molecular machines in larger systems exhibiting even macroscopic effects or generating mechanical work from chemical energy through cooperative action. The present work demonstrates the successful deposition of ordered mono- and multilayers of chemically and photochemically switchable rotaxanes on gold surfaces. Two substrates are investigated – silicon and gold. Of these materials, only gold showed to be suitable for the development of highly preferential oriented rotaxane layers. XPS indicates for both substrates that our layer-by-layer approach worked and a layer growth with every deposition step is present. NEXAFS showed that both stimuli cause an increase of the multilayer's preferential orientation and that the switching is reversible. However, these effects are only observed for the multilayers on gold surfaces.
The damage caused by ionizing radiation to DNA and proteins is the reason to treat cancer by radiation therapy. A better understanding of the molecular processes and quantification of the different damaging mechanisms is the prerequisite to develop more efficient therapies. Hereby the understanding of the processes involved in the damage to DNA are of key interest due to its central role in reproduction and mutation.
For radiation with low linear energy transfer (LET), most of the damage is caused by the secondary particles produced by scattering of the ionizing radiation with water. Thereby a multitude of species are produced, whereby especially kinetic low energy electrons, prehydrated electrons, OH-radicals and ions are of importance. With higher LET the relative amount of the direct damaging effects increases. This is especially important considering the increased usage of high LET nucleons in radiation therapy. Therefore, the quantification of the contribution to DNA damage of direct and indirect effects and the different secondary species is of high interest due to the increase of radio biological efficiency when applying high LET radiation.
Here we present an approach to investigate the relative contributions to DNA strand break yield for radiation of different LET within a single electron microscope in combination with electron scattering simulations.
The electrochemical behavior of UNS N08031 was investigated as a function of electrode potential in Green-Death solution at 40 °C. The UNS N08031 surface is in a stable passive state during cyclic potentiodynamic polarization without an initiation and/or propagation of localized corrosion. In potentiostatic polarization of UNS N08031 for 3600 s, passive current density increases with an increase in the passivation potential from 0.7 to 1.0 VSSE (silver/silver chloride reference electrode in saturated potassium chloride) Electrochemical impedance spectroscopy (EIS) and Mott-Schottky (M-S) analysis showed that a more defective n-type semiconductive passive film forms as the potential increases. X-ray photoelectron spectroscopy (XPS) revealed that passive film consists of mainly chromium and minor iron and nickel oxides. The mechanism of the defective passive film formation is discussed. The increase of the applied potential is considered to be a reason for the change in passive film stability.