Structure Formation
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Spectroscopic characterization of laser-induced luminescence for remote environmental thermometry
(2025)
Lanthanide-doped upconversion microparticles (UCMP) enable composites for luminescence thermometry with long luminescence lifetime and narrowband absorption and emission spectra. Being non-toxic, easily synthesizable, and having a bright, stable emission makes them an attractive candidate for in-vivo monitoring of key environmental parameters such as temperature. We use them to create soft, biodegradable, miniaturized seed-like robots endowed with fluorescence tags for the sustainable environmental monitoring of topsoil and air above soil environments. Our aim is an airborne platform with a sufficient signal-to-noise ratio to identify the concentration of targeted soil parameters. Here, we study the photoluminescence of Er, Yb: NaYF4 UCMPs embedded in polylactic acid (PLA) polymeric matrix to assess their suitability for remote read-out. We assessed the signal-to-noise ratio in terms of excitation intensity, UCMP concentration, working distance, and sample orientation. We evaluated the signal stability over long exposure time as well as for amplitude-modulated excitation. Finally, we carried out ratiometric and lifetime measurements of luminescence emission in order to demonstrate the feasibility of such sensors in measuring the variation of temperature. Overall, the rare-earth doped UCMPs embedded in biodegradable polymer can be used for remote thermometry, displaying a significant signal-to-noise ratio for luminescence emission detection and subsequent derivation of temperature.
Materials science research faces challenges due to diverse and evolving measurements, materials, and methods. Managing research data in a way that is understandable, comparable, and reproducible is essential for high data quality, particularly for data science and machine learning applications. In Li-ion batteries research data storage concepts and structures vary widely between institutions and researchers, leading to difficulties in data comparison and understanding. To address the issue of data structuring, battery production and characterization ontology (BPCO) is developed. The ontology builds on existing ontologies like the Platform MaterialDigital core ontology and quantities, units, dimensions, and types ontology to model standard battery production processes, characterization methods, and materials. The BPCO is based on a workflow structure to be accessible to nonexperts and, unlike highly specialized existing ontologies, models the whole production process removing the need for separate data structures and enabling the identification of dependencies between parameters. This work builds upon a previously published paper in which the taxonomy and fundamental strategies for ontology development are established. The article presents the developed ontology and its use for structuring research data in three key use cases, that is, different experiments performed to validate the ontology's capabilities, provide feedback, and ensure its applicability.
Batteries contain combinations of materials that undergo electrochemical reactions to convert chemical into electrical energy. Battery research relies on experience and know-how. Important materials and processing data can get overlooked, remain undocumented, or even lost. To bridge the gap between fundamental materials research and battery process engineering, it is essential to generate, analyze, and, most importantly, link intermediate knowledge for future use. Here, it is shown how to combine domain knowledge and a data-driven approach to understanding material–property relationships in the case of conductivity networks of carbon black. The Battery Production and Characterisation Ontology (BPCO) is employed to identify hypotheses that connect battery processing to material domain knowledge. The material's interactions between carbon black, polyvinylidene flouride, and solvents in the BPCO are characterized. These materials combine to form the classical microstructure in battery electrodes for the electrical conductivity. It is demonstrated how new links to the BPCO, verified via materials-processing relationships, and the interim results are identified as intermediate data.
Flexible transparent electrodes (FTEs) were prepared from gold nanospheres and ultra-thin gold nanowires with oleylamine ligand shell and characterised. Their colloidal inks were patterned using direct nanoimprint lithography at different particle concentrations in cyclohexane on polyethylene terephthalate substrates with a patterned polydimethylsiloxane stamp. The wire inks agglomerated upon dilution, while sphere inks did not undergo this entropy-driven mechanism. At the highest printed concentration they were still well dispersed. Plasma sintering converted the imprinted grids into conductive electrodes, but only partially removed the ligands. The sintered lines consisted of a hybrid core and a thin conductive metal shell. Wire-based shells had a coarse surface microstructure and pronounced porosity. This rendered the wire-based FTEs instable. Spheres formed smooth shells with little or no porosity, enabling a beneficial ageing process. Immediately after plasma sintering, the ratio of optical transmittance to electrical resistance for wire-based FTEs exceeded that of sphere-based FTEs. Ageing reversed this order. The instability of wire-based FTEs was overcome by PEDOT:PSS coatings.
Low-temperature printed electronics allow for the manufacturing of high-throughput, sustainable, cheap, and flexible electronics. Silver microparticles are commonly used as conductive fillers in printing pastes, owing to silver’s high conductivity and good oxidation resistance. They can be sintered at low tempera tures to achieve highly conductive prints, but a mechanistic understanding is lacking. The ecological and financial impacts of using silver are high and need to be reduced. In this thesis, I studied the low-temperature sintering of silver microflakes and spheres to screen-print recyclable and sustainable conductors. A mechanism is proposed that explains the low-temperature sin tering of silver microparticles. Mechanically weak sinter necks could be created that increased the con ductivity and could be broken up through probe sonication, allowing for recycling and reusing of the particles. Flakes led to more porous prints than spheres, which resulted in higher recycling yields. The last chapters focus on the sintering of copper microparticles. We found that polymer-capped particles required high-temperature treatments in a vacuum to have a comparable conductivity to silver-based conductors. Silver-coated copper particles reached high conductivities at low temperatures in air by forming silver necks bridging the copper cores. The particles could also be recycled and reused in a new generation of prints.
Recyclability-by-design of Printed Electronics by Low-Temperature Sintering of Silver Microparticles
(2025)
A low-temperature sintering mechanism of silver microparticles is established and used to enable the design-for-recycling of printed electronics. The formation of necks during the initial phase sintering of precipitated and atomized silver microparticles is studied. Temperature- and time-dependent in-situ analyses indicate the existence of a mobile silver species that provides efficient mass transport. The activation energy of neck formation identifies silver ion formation as the rate-limiting step of low-temperature silver sintering. It is demonstrated that resistivities of 271 times that of bulk silver can be attained after 40 minutes at 150°C. Low-temperature sintering not only reduces the energy required during thermal treatment but it yields layers that are suitable for recycling, too. The resulting layers have conductive necks that are mechanically weak enough to be broken during recycling. Printed layers are redispersed and the recycled silver powder is reused without loss of the electrical performance in new prints. Their conductivities are industrially relevant, which makes this recyclability-by-design approach promising for manufacturing more sustainable printed electronics.
This report is about the chemical formation of gels from ultrathin gold nanowires (AuNWs) and the gels’ properties. An excess of triphenylphosphine (PPh3) initiated the gelation of AuNWs with core diameters below 2 nm and an oleylamine (OAm) ligand shell dispersed in cyclohexane. The ligand exchange of OAm by PPh3 changes the AuNW-solvent interactions and leads to phase separation of the solvent to form a macroscopic gel. Small angle X-ray scattering and transmission electron microscopy indicate that hexagonal bundles in the original dispersion are dispersed, and the released nanowires entangle. Rheological analyses indicate that the resulting gel is stabilized both by physical entanglement and crosslinking of AuNWs by Van der Waals and π–π interactions. Chemically formed AuNW gels have solid-like properties and crosslinks that distinguish them from highly concentrated non-crosslinked AuNW dispersions. The AuNW gel properties can be tuned via the Au:PPh3 ratio, where smaller ratios led to stiffer gels with higher storage moduli.
The importance of shape: flakes and spheres in recyclable conductive pastes for printed electronics
(2025)
Silver microflakes and -spheres are common fillers for electrically conductive screen-printing pastes. Here, we report on the effects of filler shapes and sizes on conductivity, sintering, and recyclability. We printed pastes based on flakes and spheres, treated them at 110 °C to 300 °C, and evaluated the electrical conductivity of the resulting layers. The electrical conductivity of the layers treated at 110 °C was dominated by particle–particle contact resistances; flakes yielded layers that were five times more conductive than sphere-based layers due to differences in the particle–particle contact area. Increasing temperature led to a reduction of the resistivity of all layers through sintering. At 300 °C, prints based on spheres were 4 times more conductive than those from flakes. Tomography of the sintered structures showed that the difference was caused by a lower tortuosity factor for spheres. In a final study, we showed that silver flakes and spheres could be recycled after sintering and reused for a new generation of prints without losing electrical performance. The more porous structure of sintered flakes allowed for higher recycling yields compared to spheres. At 140 °C, 91.6% of the flakes and 69.7% of the spheres were recovered as reusable dispersions.
The water dynamics in a nanocomposite film that consists of the electrically conductive poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and cellulose nanofibrils (CNFs) have been investigated during three cycles of exposure to low and high relative humidity (RH = 5% and 85%, respectively) using quasi-elastic neutron scattering (QENS). The obtained dynamical structure factors are transformed into the imaginary part of the dynamic susceptibility to better differentiate between the individual relaxation processes. In a humid environment, two different water species are present inside the films: fast-moving bulk water and slow-moving hydration water. During the first cycle, a large amount of hydration water enhances the polymer chain mobility, eventually leading to irreversible structural rearrangements within the film. In the subsequent cycles, we observed a release of all bulk water and portions of hydration water upon drying, along with an uptake of both water species in a humid environment. The relaxation times of hydration water diffusion as a function of momentum transfer can be described by a jump-diffusion model. The obtained jump lengths, residence times, and diffusion coefficients of hydration water suggest a change in the hydration layer upon drying: water molecules around hydrophobic groups are released from the film, while the hydrogen bonds between water and hydrophilic groups are sufficiently strong to keep these molecules inside the films, even in a dry state. The QENS results can be correlated to the structural and conductive properties. In the dry state, the low hydration water content and the absence of bulk water allow for improved wetting of the CNFs by PEDOT:PSS, which eventually increases the electrical conductivity of the films.
The significant demand for energy storage systems has spurred innovative designs and extensive research on lithium-ion batteries (LIBs). To that end, an in-depth examination of utilized materials and relevant methods in conjunction with comparing electrochemical mechanisms is required. Lithium titanate (LTO) anode materials have received substantial interest in high-performance LIBs for numerous applications. Nevertheless, LTO is limited due to capacity fading at high rates, especially in the extended potential range of 0.01–3.00 V versus Li+/Li, while delivering the theoretical capacity of 293 mAh g−1. This study demonstrates how the performance of the LTO anode can be improved by modifying the manufacturing process. Altering the dry and wet mixing duration and speeds throughout the manufacturing process leads to differences in particle sizes and homogeneity of dispersion and structure. The optimized anode at 5 A g−1 (≈17C) and 10 A g−1 (≈34C) yielded 188 and 153 mAh g−1 and retained 73% and 68% of their initial capacity after 1000 cycles, respectively. The following findings offer valuable information regarding the empirical modifications required during electrode fabrication. Additionally, it sheds light on the potential to produce efficient anodes using commercial LTO powder.
