Wissenschaftliche Artikel der BAM
Filtern
Erscheinungsjahr
Dokumenttyp
- Zeitschriftenartikel (2083)
- Beitrag zu einem Tagungsband (386)
- Forschungsbericht (19)
- Beitrag zu einem Sammelband (10)
- Sonstiges (10)
- Buchkapitel (9)
- Corrigendum (3)
- Tagungsband (Herausgeberschaft für den kompletten Band) (2)
- Dissertation (1)
- Zeitschriftenheft (Herausgeberschaft für das komplette Heft) (1)
Sprache
- Englisch (2287)
- Deutsch (233)
- Mehrsprachig (3)
- Portugiesisch (1)
Schlagworte
- Additive manufacturing (69)
- Fluorescence (56)
- Nanoparticles (48)
- Concrete (47)
- SAXS (46)
- Ultrasound (38)
- Corrosion (37)
- MALDI-TOF MS (36)
- Quantum yield (36)
- Non-destructive testing (34)
Organisationseinheit der BAM
- 8 Zerstörungsfreie Prüfung (448)
- 6 Materialchemie (442)
- 1 Analytische Chemie; Referenzmaterialien (362)
- 7 Bauwerkssicherheit (228)
- 5 Werkstofftechnik (218)
- 9 Komponentensicherheit (215)
- 4 Material und Umwelt (197)
- 6.3 Strukturanalytik (168)
- 8.5 Röntgenbildgebung (139)
- 6.1 Oberflächen- und Dünnschichtanalyse (102)
- 8.2 Zerstörungsfreie Prüfmethoden für das Bauwesen (101)
- 8.0 Abteilungsleitung und andere (100)
- 5.1 Mikrostruktur Design und Degradation (80)
- 9.3 Schweißtechnische Fertigungsverfahren (79)
- 1.2 Biophotonik (74)
- 6.6 Physik und chemische Analytik der Polymere (70)
- 9.4 Integrität von Schweißverbindungen (69)
- 8.4 Akustische und elektromagnetische Verfahren (66)
- 7.5 Technische Eigenschaften von Polymerwerkstoffen (64)
- 6.2 Material- und Oberflächentechnologien (63)
- 1.1 Anorganische Spurenanalytik (61)
- 7.4 Baustofftechnologie (61)
- 6.5 Synthese und Streuverfahren nanostrukturierter Materialien (57)
- 1.4 Prozessanalytik (56)
- 4.1 Biologische Materialschädigung und Referenzorganismen (56)
- 1.7 Organische Spuren- und Lebensmittelanalytik (55)
- 3 Gefahrgutumschließungen; Energiespeicher (54)
- 1.5 Proteinanalytik (52)
- 6.0 Abteilungsleitung und andere (51)
- 8.6 Faseroptische Sensorik (50)
- 1.8 Umweltanalytik (43)
- 4.3 Schadstofftransfer und Umwelttechnologien (42)
- 5.2 Metallische Hochtemperaturwerkstoffe (42)
- 7.2 Ingenieurbau (40)
- 1.9 Chemische und optische Sensorik (38)
- 5.4 Multimateriale Fertigungsprozesse (38)
- 9.0 Abteilungsleitung und andere (35)
- 9.2 Versuchsanlagen und Prüftechnik (32)
- 4.2 Material-Mikrobiom Wechselwirkungen (30)
- 5.3 Polymere Verbundwerkstoffe (29)
- 2 Prozess- und Anlagensicherheit (28)
- 4.0 Abteilungsleitung und andere (28)
- 4.5 Kunst- und Kulturgutanalyse (28)
- 5.5 Materialmodellierung (27)
- 5.6 Glas (27)
- S Qualitätsinfrastruktur (27)
- 7.6 Korrosion und Korrosionsschutz (26)
- 2.1 Sicherheit von Energieträgern (25)
- 4.4 Thermochemische Reststoffbehandlung und Wertstoffrückgewinnung (24)
- 9.5 Tribologie und Verschleißschutz (23)
- 9.6 Additive Fertigung metallischer Komponenten (23)
- 8.1 Sensorik, mess- und prüftechnische Verfahren (22)
- VP Vizepräsident (22)
- VP.1 eScience (22)
- 7.1 Baustoffe (21)
- 1.3 Instrumentelle Analytik (19)
- 3.1 Sicherheit von Gefahrgutverpackungen und Batterien (17)
- 5.0 Abteilungsleitung und andere (17)
- 1.6 Anorganische Referenzmaterialien (16)
- S.2 Digitalisierung der Qualitätsinfrastruktur (16)
- 7.7 Modellierung und Simulation (15)
- 1.0 Abteilungsleitung und andere (13)
- 7.0 Abteilungsleitung und andere (13)
- P Präsident (11)
- 3.2 Gefahrguttanks und Unfallmechanik (10)
- 3.5 Sicherheit von Gasspeichern (10)
- P.0 Präsident und andere (10)
- 6.7 Materialsynthese und Design (9)
- 7.3 Brandingenieurwesen (9)
- 6.4 Materialinformatik (8)
- 3.4 Sicherheit von Lagerbehältern (7)
- S.3 Ökodesign und Energieverbrauchskennzeichnung (7)
- 3.6 Elektrochemische Energiematerialien (6)
- S.1 Qualität im Prüfwesen (5)
- 3.0 Abteilungsleitung und andere (4)
- 8.3 Thermografische Verfahren (4)
- 4.6 Molekulare und angewandte Entomologie (3)
- 2.0 Abteilungsleitung und andere (2)
- 2.2 Prozesssimulation (2)
- 2.3 Einstufung von Gefahrstoffen und -gütern (1)
- 2.5 Konformitätsbewertung Explosivstoffe/Pyrotechnik (1)
- 3.3 Sicherheit von Transportbehältern (1)
- KM Kommunikation, Marketing (1)
- PST Präsidiale Stabsstelle (1)
- VP.2 Informationstechnik (1)
Paper des Monats
- ja (68)
Classical film radiography is a well-established NDT technique and it is most commonly used for testing weld seams and corroded pipes e.g. in oil and gas industry or in nuclear power plants. In the course of digitization, digital detector arrays (DDA) are finding their way into industrial applications and are replacing film radiography step by step. This study deals with the latest generation of DDAs, the photon counting and energy resolving detectors (PCD), and their characteristics compared to charge integrating detectors (CID). No matter which technology to use, radiography still lacks a general issue: A three-dimensional object is projected onto a two dimensional image. Of course, advanced computed tomography (CT) algorithms exist since many years, but if the object to investigate is too large to fit into the manipulation system or its shape is not appropriate, CT is not feasible or sensible to be applied. To overcome this limitation, numerous laminographic algorithms have been developed in the past. In this study, photon counting detectors are used in combination with co-planar translational laminography to gain reconstructed three-dimensional volumes. Both laminographic testing and PCDs require a serious knowledge of many parameters that can influence the image quality in the resulting datasets. These are e.g. the detector efficiency and calibration procedure, setting of energy thresholds, exposure data, number of projections, beam length correction and spatial resolution. The use of PCDs yields more variables to be considered compared to CIDs. The most important parameters in laminographic testing and in the use of PCDs are described in this study and limits are discussed.
Non-destructive testing (NDT) helps to find material defects without having an influence on the material itself. It is applied as a method of quality control, for online structural health monitoring, and for inspection of safety related components. Due to the ability of automation and a simple test setup ultrasonic testing is one major NDT technique next to several existing options. Whereas contact technique allows the use of higher frequencies of some MHz and phased array focusing, air-coupled ultrasonic testing (ACUT) shows different advantages. Most significant for ACUT is the absence of any coupling fluid and an economical test procedure respective time and costs. Both contact technique and ACUT have been improved and enhanced during the past years. One important enhancement is the development of airborne transducers based on ferroelectrets, like charged cellular polypropylene (cpp), which makes the application of any matching layers being mandatory in conventional piezoelectric transducers unnecessary. In this contribution we show ultrasonic inspection results of specimens made of carbon- and glass-fibre-reinforced plastic. These specimens include defects represented by drill holes and artificial delaminations of various size and depth. We compare inspection results achieved by using contact technique to those achieved by ACUT. For ACUT, conventional piezoelectric transducers and transducers based on cpp were used, both focused as well as non-focused types. Contact inspections were performed with a multi-channel matrix array probe. Once the inspection data is recorded it can be analysed in order to detect and evaluate defects in the specimen. We present different analysing strategies and compare these regarding detection rate and sizing of defects.
A simple batch test leaching procedure is used in many countries, as a compliance test, to evaluate the leaching of mainly inorganic substances from soil. However, agitating certain types of soil and then passing the solution through a membrane filter with 0.45-µm pores yields filtrates that have been colored by the colloidal particles. These colloids might affect the results of the inorganic substances obtained in the batch tests. In this study, we evaluated the effects of colloidal particles on the results and the reproducibility of batch tests on contaminated soil using different agitation methods and membrane filters with different pore sizes. The leaching behaviors of As, Pb, Se, F and Cl from three types of soil were studied. The As and Pb concentrations in the leachates of some types of soil were clearly affected by the amount of colloidal particles with a diameter of 0.10–0.45 µm and by the agitation method used. This was probably because As and Pb were present mainly in the particulate form in the leachate that had been passed through a membrane filter with 0.45-µm pores. This is not the case for every type of soil. The results of batch leaching tests showed that not only dissolved but also colloidal forms with a diameter of 0.10–0.45 µm might be included and that the existence of colloidal particles in the leachate decreases the batch leaching test reproducibility.
Two novel species of the fungal genus Ochroconis, O. lascauxensis and O. anomala have been isolated from the walls of the Lascaux Cave, France. The interest in these fungi and their melanins lies in the formation of black stains on the walls and rock art which threatens the integrity of the paintings. Here we report solid-state cross polarization magic-angle spinning 13C and 15N nuclear magnetic resonance (NMR) spectroscopy and surface-enhanced Raman spectroscopy (SERS) of the melanins extracted from the mycelia of O. lascauxensis and O. anomala in order to known their chemical structure. The melanins from these two species were compared with those from other fungi. The melanins from the Ochroconis species have similar SERS and 13C and 15N NMR spectra. Their chemical structures as suggested by the data are not related to 3,4-dihydroxyphenylalanine, 5,6-dihydroxyindole or 1,8-dihydroxynaphthalene precursors and likely the building blocks from the melanins have to be based on other phenols that react with the N-terminal amino acid of proteins. The analytical pyrolysis of the acid hydrolysed melanin from O. lascauxensis supports this assumption.
As part of the Qumran project conducted at the Federal Institute for Materials Research and Testing (BAM) in Berlin between 2007 and 2010, my colleagues and I developed a new, integrated methodology for determining the original and acquired properties of highly heterogeneous Dead Sea Scrolls. The purpose of this methodology is to help scholars determine the provenance of fragments of the scrolls and sort and compare them more easily than in the past. Since our measurements allowed us to differentiate between the minerals originating from the production processes and the sediments accrued during storage in the caves in Qumran, we were able to reconstruct the treatment of hides and discovered that at least two distinct parchmentproduction techniques co-existed at the beginning of the common era.
The reconstruction of workmanship on animal hides in Antiquity raised doubts about the validity of the current definition of parchment, which is based on a production technique known from the Middle Ages. We hope that our current work will also help researchers understand the characteristic properties of gewil, qelaf and dukhsustos better.¹
The evolution and socio-geographic distribution of writing inks in late Antiquity and the early Middle Ages are the second focus of our investigative work at BAM.
We use X-ray fluorescence analysis (XRF) to determine the chemical composition of inks and NIR reflectography for their typology. We are amply assisted in our ambitious enterprise by codicologists and palaeographers who have adopted our methodology and conduct field studies of their own.
Our current projects focus on the material analysis of the writing materials
kept in the Taylor-Schechter Collection at Cambridge University Library,
which houses the largest collection of Cairo Geniza fragments, about 190,000.
Although Geniza manuscripts have attracted a great deal of scholarly attention,
the material aspects of these documents seem to have been largely neglected.
The current study aims to obtain information on the composition of the writing
supports and the inks that were used, the production of the original manuscripts
and the history of their degradation. The collected data should supplement the
description based on Hebrew palaeography and codicology. Moreover, a characterisation
of the writing materials would provide insights on trade, local production
techniques and social structures. The tabulated results have the potential to
be used as geo-chronological markers if sufficient data is collected.
For our study, we chose Hebrew legal documents and letters from three communities
that co-existed in Fustat (today Cairo) in the 11th century: the Jerusalemite
(or ‘Palestinian’) community, the Babylonian community and the Karaites, three
different communities with different scribal traditions. In addition to this, we
studied non-biblical scrolls attributed to the Palestinian and Babylonian communities.
The question we addressed was whether we can correlate the use of a
specific type of ink to an objective criterion.
For our analysis at Cambridge University Library, we used a number of protocols
developed at BAM (Bundesanstalt für Materialforschung und -prüfung) in
Berlin and at the Centre for Study of Manuscript Cultures, University of Hamburg
(CSMC). These include reflectographic examination followed by non-destructive
X-ray fluorescence (XRF) analysis using transportable instruments so that the
analysis can be carried out in situ.
We have illustrated our approach here by providing two examples. The first one
describes our investigation of the leather fragment containing a portion of the
Babylonian Talmud on its hair side (TS Misc.26.53.17). The second example illustrates
our ability to compare iron-gall inks using the XRF method. In this case,
we explored the question of the codicological attribution of three fragments (TS
F17.4, TS 12.755 and TS 12.756) to the same Talmud manuscript.
The development of alkali‐activated materials (AAMs) as an alternative to Portland cement (PC) has seen significant progress in the past decades. However, there still remains significant uncertainty regarding their long term performance when used in steel‐reinforced structures. The durability of AAMs in such applications depends strongly on the corrosion behaviour of the embedded steel reinforcement, and the experimental data in the literature are limited and in some cases inconsistent. This letter elucidates the role of the chemistry of AAMs on the mechanisms governing passivation and chloride‐induced corrosion of the steel reinforcement, to bring a better understanding of the durability of AAM structures exposed to chloride. The corrosion of the steel reinforcement in AAMs differs significantly from observations in PC; the onset of pitting (or the chloride ‘threshold’ value) depends strongly on the alkalinity, and the redox environment, of these binders. Classifications or standards used to assess the severity of steel corrosion in PC appear not to be directly applicable to AAMs due to important differences in pore solution chemistry and phase assemblage.
Proben mit einer Mittelkerbe aus Polyamid 66 mit 35% Gewichtsan-teil an Kurzglasfaser (PA-GF35) wurden im Spritzgießverfahren hergestellt und in einem ungeschädigten und durch Schwingbeanspruch geschädigten Zustand mittels Röntgenverfahren charakterisiert. Sowohl die Faserorientierungsverteilung als auch die Riss-/Mikrorissbildung wurden mit der Röntgenrefraktionstopographie in einem SAXS-Aufbau und dem Diffraction-Enhanced-Imaging am Synchrotron (BESSY II) analysiert. Beide Verfahren spiegeln in guter Übereinstimmung die Charakteristiken dieser Werkstoffklasse in Bezug auf die Fertigungsqualität und die Schädigungsme-chanismen wider.
Detection of the electronic structure of iron-(III)-oxo oligomers forming in aqueous solutions
(2017)
The nature of the small iron-oxo oligomers in iron-(III) aqueous solutions has a determining effect on the chemical processes that govern the formation of nanoparticles in aqueous phase. Here we report on a liquid-Jet photoelectron-spectroscopy experiment for the investigation of the electronic structure of the occurring iron-oxo oligomers in FeCl3 aqueous solutions. The only iron species in the as-prepared 0.75 M solution are Fe3+ monomers. Addition of NaOH initiates Fe3+ hydrolysis which is followed by the formation of iron-oxo oligomers. At small enough NaOH concentrations, corresponding to approximately [OH]/[Fe] = 0.2–0.25 ratio, the iron oligomers can be stabilized for several hours without engaging in further aggregation. Here, we apply a combination of non-resonant as well as iron 2p and Oxygen 1s resonant photoelectron spectroscopy from a liquid microjet to detect the electronic structure of the occurring species. Specifically, the oxygen 1s partial electron yield X-ray absorption (PEY-XA) spectra are found to exhibit a peak well below the onset of liquid water and OH (aq) absorption. The iron 2p absorption gives rise to signal centered between the main absorption bands typical for aqueous Fe3+. Absorption bands in both PEY-XA spectra are found to correlate with an enhanced photoelectron Peak near 20 eV binding energy, which demonstrates the sensitivity of resonant photoelectron (RPE) spectroscopy to mixing between iron and ligand orbitals. These various signals from the iron-oxo oligomers exhibit Maximum intensity at [OH]/[Fe] = 0.25 ratio. For the same ratio, we observe changes in the pH as well as in complementary Raman spectra, which can be assigned to the Transition from monomeric to oligomeric species. At approximately [OH]/[Fe] = 0.3 we begin to observe particles larger than 1 nm in radius, detected by small-angle X-ray scattering.
Health monitoring von größeren Strukturen erfordert die Betrachtung der gesamten Struktur, indem sowohl jener Bereich, der experimentell behandelt wird, als auch derjenige, der einer analytischen mechanischen Untersuchung unterzogen wird, in einem Gesamtzusammenhang erfasst wird. Die umfassende Behandlung des Problems gelingt dann in einer Gesamtmatrix, die im Beitrag vorgestellt wird. Auf eine Erweiterung der Methode zur Detektierung anwachsender Schädigungen wird hingewiesen.
Efficiency Evaluation of Extraction Methods for Analysis of OCPs and PCBs in Soils of Varying TOC
(2017)
Organochlorine pesticides and polychlorinated biphenyls are toxic, carcinogenic, and have a high potential for bioaccumulation. Due to their stability, they are still considered an environmental problem even though the use of most of them has been phased out several decades ago. Soil is a matrix which can retain these contaminants to a great extent. This ability is often associated with the total organic carbon content (TOC). In order to judge the pollution status of soil and to make monitoring data more easily comparable a simple, yet robust extraction method is needed. Agitation solid-liquid-extraction is well suited for this purpose. However, the influence of TOC on the analyte recovery has to be known. For the presented study, 12 organochlorine pesticides and 7 polychlorinated biphenyls were spiked into four model soils with organic carbon contents between 1.6% - 13.3%. The matrices were extracted using solid-liquid extraction between 45 minutes and 16 hours. For comparison, all soils were also extracted using pressurised liquid extraction and Soxhlet extraction. After clean-up the extracts were measured using a gas chromatography-mass spectrometry (GC-MS) system. Statistical analysis of the results implied that the TOC content of the soils did not have significant influence on the extraction efficiency. A longer solid-liquid extraction time did not necessarily increase analyte recovery: Extraction for one hour resulted in 88% recovery while 16 hour extraction led to 89%. Thus, the efficiency of all the methods was comparable for all model soils. Additional investigations regarding GC liner performance highlighted the need for isotopically labelled standards during the analysis of thermolabile pesticides.
Although the concept of structural water that is bound inside hydrophobic pockets and helps to stabilize protein structures is well established, water has rarely found a similar role in supramolecular polymers. Water is often used as a solvent for supramolecular polymerization, however without taking the role of a comonomer for the supramolecular polymer structure. We report a low–molecular weight monomer whose supramolecular polymerization is triggered by the incorporation of water. The presence of water molecules as comonomers is essential to the polymerization process. The supramolecular polymeric material exhibits strong adhesion to surfaces, such as glass and paper. It can be used as a water-activated glue, which can be released at higher temperatures and reused many times without losing its performance.
Fracture mechanics based component design requires appropriate fracture mechanics toughness data with respect to both, loading rate as well as test temperature. Taking high-rate loading into account such as with accidental scenarios, different standards such as ASTM E 1820 or BS 7448-3 provide some information on dynamic fracture mechanics testing. Nevertheless, the designations differ so that a validation of the own material specific test method used for dynamic R-curve determination is mandatory. In order to address this for ductile cast iron materials an experimental method for the reliable determination of dynamic J-integral crack resistance curves at -40 °C following the multiple specimen approach has been established and validated. The experimental concept offers some additional valuable features. Single values of dynamic crack initiation toughness can be determined using a single specimen technique based on crack sensors. Furthermore, an experimentally independent method is provided according to which CTOD δ5 R-curves can be established. The focus of the present paper is on the validation of the experimental low blow technique using a drop tower test system.
A drop tower test system was developed and set up to perform low blow tests at temperatures down to -40 °C. The system allows for a variation of the impact mass and height and was optimized for testing of ductile cast iron at stress intensity rates from approximately 5∙10⁴ to 3∙10⁵ MPa√ms⁻¹. This range of loading rate is characteristic for instance with crash scenarios of heavy sectioned DCI casks for radioactive materials. In order to address characteristic challenges of impact tests (test duration of microseconds up to milliseconds, inertial effects, signal oscillations), an appropriate full bridge strain gage method for the measurement of force directly on the specimen as well as a non-contact measurement of load line displacement using an optical extensometer have been developed and validated.
The low blow test requires either to prevent bouncing strikes of the hammer by using the stop block technique or to catch the hammer after its first strike. Both options are not part of the experimental concept and setup which have been realized here. The paper describes investigations which have been performed in order to make sure that bouncing strikes of the hammer do not cause additional crack extension in the specimen. This is necessary to ensure a unique relation between the work done and the achieved crack extension. The investigations covered the analysis of limit loads of the specimen with respect to the measured force. The measured stiffness of the specimen was assessed and signals of crack sensors were analyzed. Furthermore, an analysis of the mechanical behavior of the loading system and the specimen by optical observation was performed. Corresponding results are discussed in the paper. It had finally been proven that additional crack extension in the specimen due to bouncing strikes of the hammer is not to be expected under the given conditions of test setup, material and loading. It can be seen as a major experimental advantage that the striker does not have to be catched after the low blow test.
Quantification of nanoparticle (NP) uptake in cells or tissues is very important for safety assessment. Often, electron microscopy based approaches are used for this purpose, which allow imaging at very high resolution. However, precise quantification of NP numbers in cells and tissues remains challenging. The aim of this study was to present a novel approach, that combines precise quantification of NPs in individual cells together with high resolution imaging of their intracellular distribution based on focused ion beam/ scanning electron microscopy (FIB/SEM) slice and view approaches.
The structural and magnetic properties of magnetic multi-core particles were determined by numerical inversion of small angle scattering and isothermal magnetisation data. The investigated particles consist of iron oxide nanoparticle cores (9 nm) embedded in poly(styrene) spheres (160 nm). A thorough physical characterisation of the particles included transmission electron microscopy, X-ray diffraction and asymmetrical flow field-flow fractionation. Their structure was ultimately disclosed by an indirect Fourier transform of static light scattering, small angle X-ray scattering and small angle neutron scattering data of the colloidal dispersion. The extracted pair distance distribution functions clearly indicated that the cores were mostly accumulated in the outer surface layers of the poly(styrene) spheres. To investigate the magnetic properties, the isothermal magnetisation curves of the multi-core particles (immobilised and dispersed in water) were analysed. The study stands out by applying the same numerical approach to extract the apparent moment distributions of the particles as for the indirect Fourier transform. It could be shown that the main peak of the apparent moment distributions correlated to the expected intrinsic moment distribution of the cores. Additional peaks were observed which signaled deviations of the isothermal magnetisation behavior from the non-interacting case, indicating weak dipolar interactions.
The paper presents a new method for the determination and evaluation of tafel factors using gel-type electrolytes and electrochemical frequency modulation technique (EFM). This relatively new electrochemical method offers the possibility to determine both polarization resistances and tafel factors within one measurement and in short measuring intervals. Starting from a comprehensive parameter study it is shown that a direct relationship between the two values exists that can be described mathematically. This contribution presents the determined tafel factors for the system gel-type electrolyte/zinc and discusses their applicability and their limits.
Water and aqueous reagents are essential in any biological process or system. But apart from a few special low vapor-pressure cases, liquids have not been accessible to any technique requiring UHV conditions. EnviroESCA opens up this exciting field of applications.
In this paper first results from water based samples are presented as a proof of concept to demonstrate the special capabilities of EnviroESCA analyzing liquid samples. The following solutions were investigated under near ambient pressure conditions: i.) water, ii.) brine, iii.) an oil in water dispersion, iv.) aqueous iron(II) sulfate heptahydrate, and v.) a suspension of nano silver particles in water.
An UCST-type copolymer of acrylamide (AAm) and acrylonitrile (AN) (poly(AAm-co-AN)) was prepared by reversible addition fragmentation chain transfer (RAFT) polymerization and its temperature-induced phase transition and aggregation behaviour studied by turbidimetry, static and dynamic light scattering, small angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM) measurements. The phase transition temperature was found to increase with increasing AN content in the copolymer, concentration of the solutions and copolymer chain length. A significant effect was observed onto the phase transition temperature by addition of different electrolytes into the copolymer solution. The copolymer chains were aggregated below the phase transition temperature and disaggregated above it. The size of the aggregates increases with increasing AN contents and concentration of the copolymer solutions below the phase transition temperature. The copolymer chains were expanded and weekly associated in solution above the phase transition temperature. A model is proposed to explain such association–aggregation behaviour of poly(AAm-co-AN) copolymers depending on AN contents and concentration of the copolymer solutions as a function of temperature.
A controlled, reproducible, gram-scale method is reported for the covalent functionalization of graphene Sheets by a one-pot nitrene [2+1] cycloaddition reaction under mild conditions. The reaction between commercially available 2,4,6-trichloro-1,3,5-triazine and sodium azide with thermally reduced graphene oxide (TRGO) results in defined dichlorotriazine-functionalized sheets. The different reactivities of the chlorine substituents on the functionalized graphene allow stepwise post-modification by manipulating the temperature.
This new method provides unique access to defined bifunctional 2D nanomaterials, as exemplified by chiral surfaces and multifunctional hybrid architectures.
Recently, there has been a rise in freshwater harmful algal blooms (HABs) globally, as well as increasing aquaculture practices. HABs can produce cyanotoxins, many of which are hepatotoxins. An ultra-performance liquid chromatography tandem mass spectrometry method was developed and validated for nine cyanotoxins across three classes including six microcystins, nodularin, cylindrospermopsin and anatoxin-a. The method was used to analyse free cyanotoxin(s) in muscle (n = 34), liver (n = 17) and egg (n = 9) tissue samples of 34 fish sourced from aquaculture farms in Southeast Asia. Conjugated microcystin was analysed by Lemieux oxidation to ascertain the total amount of microcystin present in muscle. Some tilapia accumulated free microcystin-LR in the muscle tissue at a mean of 15.45 μg/kg dry weight (dw), with total microcystin levels detected at a mean level of 110.1 μg/kg dw, indicating that the amount of conjugated or masked microcystin present in the fish muscle accounted for 85% of the total. Higher levels of cyanotoxin were detected in the livers, with approximately 60% of those tested being positive for microcystin-LR and microcystin-LF, along with cylindrospermopsin. Two fish from one of the aquaculture farms contained cylindrospermopsin in the eggs; the first time this has been reported. The estimated daily intake for free and total microcystins in fish muscle tissue was 2 and 14 times higher, respectively, than the tolerable daily intake value. This survey presents the requirement for further monitoring of cyanotoxins, including masked microcystins, in aquaculture farming in these regions and beyond, along with the implementation of guidelines to safeguard human health.