6.1 Oberflächen- und Dünnschichtanalyse
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- 6.6 Physik und chemische Analytik der Polymere (43) (entfernen)
Determining thermal transitions in thin polymer layers by means of spectroscopic ellipsometry
(2023)
Thin polymer layers have enormous technical significance as polymer coatings on materials are very cost-effective for tailoring properties of surfaces. Apart from technical aspects in their use, thin polymer layers can be used to determine dimensional aspects in properties of material, such as confinement effects.
In this work, we investigated several different polymer layer materials and determined their glass transition region by means of temperature-dependent spectroscopic ellipsometry. We have optimised our fitting procedure of the ellipsometric data produced in temperature ramp experiments. By this, we could measure the dependence of Tg on the layer thickness in a wide variety of thickness values, proving the existence of confinement effects in the investigated systems. We compare numerical methods for determining the location of the glass transition and discuss the possibilities of different analysis methods when determining thermal transitions. We also discuss the simultaneous existence of these transitions and annealing effects and the implications on the accuracy of the determined data.
Ionizing radiation damage to DNA plays a fundamental role in cancer therapy. X-ray photoelectron-spectroscopy (XPS) allows simultaneous irradiation and damage monitoring. Although water radiolysis is essential for radiation damage, all previous XPS studies were performed in vacuum. Here we present near-ambient-pressure XPS experiments to directly measure DNA damage under water atmosphere. They permit in-situ monitoring of the effects of radicals on fully hydrated double-stranded DNA. The results allow us to distinguish direct damage, by photons and secondary low-energy electrons (LEE), from damage by hydroxyl radicals or hydration induced modifications of damage pathways. The exposure of dry DNA to x-rays leads to strand-breaks at the sugar-phosphate backbone, while deoxyribose and nucleobases are less affected. In contrast, a strong increase of DNA damage is observed in water, where OH-radicals are produced. In consequence, base damage and base release become predominant, even though the number of strand-breaks increases further.
The glass transition behavior of thin films of poly(bisphenol A carbonate) (PBAC) was studied employing ellipsometry. The glass transition temperature increases with the reduction of the film thickness. This result is attributed to the formation of an adsorbed layer with a reduced mobility compared to bulk PBAC. Therefore, for the first time, the growth kinetics of the adsorbed layer of PBAC was investigated, prepared by leaching samples from a 200 nm thin film which were annealed for several times at three different temperatures. The thickness of each prepared adsorbed layer was measured by multiple scans using atomic force microscopy (AFM). Additionally, an unannealed sample was measured. Comparison of the measurements of the unannealed and the annealed samples provides proof of a pre-growth regime for all annealing temperatures which was not observed for other polymers. For the lowest annealing temperature after the pre-growth stage only a growth regime with a linear time dependence is observed. For higher annealing temperatures the growth kinetics changes from a linear to a logarithmic growth regime at a critical time. At the longest annealing times the films showed signs of dewetting where segments of the adsorbed film were removed from the substrate (dewetting by desorption). The dependence of the surface roughness of the PBAC surface on annealing time also confirmed that the films annealed at highest temperatures for the longest times desorbed from the substrate.
In-situ monitoring of water dependent DNA and protein radiation damage by near-ambient-pressure XPS
(2023)
X-ray photoelectron-spectroscopy (XPS) allows simultaneous irradiation and damage monitoring. Although water radiolysis is essential for radiation damage, all previous XPS studies were performed in vacuum. Here we present near-ambient-pressure XPS experiments to directly measure DNA damage under water atmosphere. They permit in-situ monitoring of the effects of radicals on fully hydrated double-stranded DNA. Our results allow us to distinguish direct damage, by photons and secondary low-energy electrons (LEE), from damage by hydroxyl radicals or hydration induced modifications of damage pathways. The exposure of dry DNA to x-rays leads to strand-breaks at the sugar-phosphate backbone, while deoxyribose and nucleobases are less affected. In contrast, a strong increase of DNA damage is observed in water, where OH-radicals are produced. In consequence, base damage and base release become predominant, even though the number of strand-breaks increases further.
The VAMAS/TWA 45 Project 2 “Development of standardized methodologies for characterisation of microplastics with microscopy and spectroscopy methods” involving 85 participants around the world is primarily discussed with respect to the results received and a first data evaluation. Status of the Project "Guidelines for defining reference materials for plastic degradation in marine environment" is reported and two new project proposals are presented: "Development of standardized methodologies for characterisation of nanoplastics (starting soon, BAM as leader?) and "Development of analytical protocols for the identification and quantification of microplastics of fibrous shape (still in negotiation)".
Preliminary results of an interlaboratory comparison on microplastics organised by plasticsfate
(2023)
Microplastics are everywhere in the environment, but analytics is challenging. Since harmonisation is missing as well es suitable reference materials, BAM did under th umbrella of VAMAS funded by the EU Horizon 2020 project PlasticsFate a ILC for microplastic detection methods. Methods adressed were IR, Raman, Py-GC/MS and TED-GC/MS. The talk gives a first presentation and evaluation on the results.
Interactions between a polymer and a substrate interface play a vital role in understanding the improvement in thin film material properties as well as serving as a model for nanocomposites. For any non-repulsive polymer-substrate interactions, polymer segments form an irreversibly adsorbed layer and show a slowdown in the glassy dynamics and thus an increase in the thermal glass transition temperature compared to the bulk-like values. The growth kinetics of the adsorbed layer showed a deviation for both poly (bisphenol-A carbonate) (PBAC) and polysulfone (PSU), two bulky polymers containing a functional group (phenyl ring) in the backbone, compared to conventional polymers previously studied like poly-2-vinyl pyridine (P2VP). This deviation was attributed to the bulkiness of the phenyl rings. . Further investigations into the influence of the adsorbed layer on glassy dynamics were conducted. The molecular mobility and glass transition for thin films of PBAC and PSU were compared to bulk samples of each polymer. Broadband dielectric spectroscopy, atomic force microscopy, and ellipsometry were primarily used and additionally supported by sum frequency generation spectroscopy.
Since microplastics (MPs) can be found everywhere and are becoming a problem of high concern, it is necessary to understand their physico-chemical properties. To obtain reliable analytical data a set of validated methods for sampling, sample preparation, detection, and data evaluation are needed.
To meet these needs an interlaboratory comparison (ILC) with 84 participants worldwide has been organized under the international pre-standardisation platform VAMAS (www.vamas.org/twa45/) as Project 2 “Development of standardized methodologies for characterisation of microplastics with microscopy and spectroscopy methods” within the Technical Working Area TWA 45 “Micro and Nano Plastics in the Environment”. In this ILC thermo-analytical methods (Py-GC/MS and TED-GC/MS) and vibrational methods (µ-Raman and µ-FTIR) have been tested and compared by providing a set of microplastic representative test materials and measurement protocols developed at BAM. The defined measurands were: particle number concentration, particle size distribution (PSD), and polymer identity and mass content. To increase the statistical quality, 6 samples were shipped together with blank samples. Hence, the ILC provides information on precision and accuracy of the results obtained with different methods as well as strengths and limitations of the proposed protocols.
Since microplastics (MPs) can be found everywhere and are becoming a problem of high concern, it is necessary to understand their occurrence and fate in the environment. However, to obtain data of high quality is very challenging, since measurement operating procedures differ from laboratory to laboratory. Currently, there are no standardized methods to analyze microplastics. One promissing possibility to adress standardization of the methodology and operating procedures are interlaboratory comparisons (ILCs). In this contribution we report the first results of an ILC on microplastic detection methods organized under the pre-stantdardisation plattform of VAMAS (www.vamas.org/twa45/) as Project 2 “Development of standardized methodologies for characterisation of microplastics with microscopy and spectroscopy methods”, within the Technical Working Area TWA 45 “Micro and Nano Plastics in the Environment”. The ILC has gathered 84 participants all over the world representing all continents. BAM, as the project leader, produced a set of reference microplastic materials, which have been distributed to all the participants together with the measurement protocols and reporting data templates.