Scientific publications

The controlled functionalization of surfaces is of utmost importance for many applications. Surface-initiated living anionic polymerization (SI-LAP) offers a well-adjustable, uniform functionalization without the necessity of metal catalysts for polymerization. However, this technique is rarely studied for functional monomers, such as different methacrylates. The present study investigated the SI-LAP of different methacrylate monomers on porous polystyrene microparticles. Starting with methyl methacrylate (MMA) as the model monomer, the reaction kinetics and the living character of the polymerization at the particles’ surface are discussed. The reaction conditions were transferred to more functional methacrylates, for example, 2-(trimethylsilyloxy)ethyl methacrylate (HEMA-TMS). The functionalization in the particle’s interior enables the preparation of fluorescent particles by applying post-modification protocols of the poly(hydroxyethyl methacrylate) (PHEMA) moieties with fluorescein isothiocyanate. Moreover, ferrocenylmethyl methacrylate (FMMA) polymerization leads to stimuli-responsive particles with an adjustable functional polymer content of 7 to 51%. Electrochemical studies for the latter polymer poly(ferrocenylmethyl methacrylate) (PFMMA) on the surface offered remarkable long-term stability upon addressing the redox responsiveness of the ferrocene moieties over 1000 cycles using electrochemistry. The synthesis strategy enables access to various applications, such as battery anodes, redox-flow batteries, or ion sorbents.

Hybrid dielectrics were prepared from dispersions of nanoparticles with gold cores (diameters from 2.9 nm to 8.2 nm) and covalently bound thiol-terminated polystyrene shells (5000 Da and 11 000 Da) in toluene. Their microstructure was investigated with small angle X-ray scattering and transmission electron microscopy. The particles arranged in nanodielectric layers with either face-centered cubic or random packing, depending on the ligand length and core diameter. Thin film capacitors were prepared by spin-coating inks on silicon substrates, contacted with sputtered aluminum electrodes, and characterized with impedance spectroscopy between 1 Hz and 1 MHz. The dielectric constants were dominated by polarization at the gold–polystyrene interfaces that we could precisely tune via the core diameter. There was no difference in the dielectric constant between random and supercrystalline particle packings, but the dielectric losses depended on the layer structure. A model that combines Maxwell–Wagner–Sillars theory and percolation theory described the relationship of the specific interfacial area and the dielectric constant quantitatively. The electric breakdown of the nanodielectric layers sensitively depended on particle packing. A highest breakdown field strength of 158.7 MV m−1 was found for the sample with 8.2 nm cores and short ligands that had a face-centered cubic structure. Breakdown apparently is initiated at the microscopic maxima of the electric field that depends on particle packing. The relevance of the results for industrially produced devices was demonstrated on inkjet printed thin film capacitors with an area of 0.79 mm2 on aluminum coated PET foils that retained their capacity of 1.24 ± 0.01 nF@10 kHz during 3000 bending cycles.

Self-assembled nanoparticles (NPs) in superlattices are in close contact. Their dense packing and the proximity of aligned facets can facilitate coalescence and enable crystal lattices to fuse at temperatures below the bulk melting point. This phenomenon could be applied in nanodevice manufacture. We study NP fusion in superlattices in liquid and dry environments at controlled temperatures using electron microscopy at minimized electron doses. We found that coalescence of self-assembled gold NPs (AuNPs, diameter 8.1 ± 0.4 nm) depended on their arrangement. A double layer of AuNPs in a hexagonally close packed superlattice started to coalesce within 2 min at a temperature of 70 °C in cyclohexane but remained stable for 30 min at 98 °C when it was dry. AuNPs assembled in hexagonal monolayers coalesced after 5 min at 75 °C in cyclohexane. The mobility of the ligand shells and the interfacial gold atoms and the sparse ligand coverage on (111) facets likely facilitated this AuNP coalescence at low temperatures.

An ontology for the structured storage, retrieval, and analysis of data on lithium-ion battery materials and electrode-to-cell production is presented. It provides a logical structure that is mapped onto a digital architecture and used to visualize, correlate, and make predictions in battery production, research, and development. Materials and processes are specified using a predetermined terminology; a chain of unit processes (steps) connects raw materials and products (items) of battery cell production. The ontology enables the attachment of analytical methods (characterization methods) to items. Workshops and interviews with experts in battery materials and production processes are conducted to ensure that the structure is conformable both for industrial-scale and laboratory-scale data generation and implementation. Raw materials and intermediate products are identified and defined for all steps to the final battery cell. Steps and items are defined based on current standard materials and process chains using terms that are in common use. Alternative structures and the connection of the ontology to other existing ontologies are discussed. The contribution provides a pragmatic, accessible way to unify the storage of materials-oriented lithium-ion battery production data. It aids the linkage of such data with domain knowledge and the automation of data analysis in production and research.

Lithium-ion and sodium-ion batteries (LIBs and SIBs) are crucial in our shift toward sustainable technologies. In this work, the potential of layered boride materials (MoAlB and Mo2AlB2) as novel, high-performance electrode materials for LIBs and SIBs, is explored. It is discovered that Mo2AlB2 shows a higher specific capacity than MoAlB when used as an electrode material for LIBs, with a specific capacity of 593 mAh g−1 achieved after 500 cycles at 200 mA g−1. It is also found that surface redox reactions are responsible for Li storage in Mo2AlB2, instead of intercalation or conversion. Moreover, the sodium hydroxide treatment of MoAlB leads to a porous morphology and higher specific capacities exceeding that of pristine MoAlB. When tested in SIBs, Mo2AlB2 exhibits a specific capacity of 150 mAh g−1 at 20 mA g−1. These findings suggest that layered borides have potential as electrode materials for both LIBs and SIBs, and highlight the importance of surface redox reactions in Li storage mechanisms.

In the field of carbanionic polymerization bifunctional initiators permit the synthesis of complex triblock copolymer structures. Using 1,3-bis(1-phenylethenyl)benzene (PEB), isoprene was polymerized in cyclohexane, yielding a high content of 1,4-PI units of 93%. Subsequently, 3 hydroxyl groups were introduced simultaneously both in α- and ω-position by means of end-functionalization of the living anionic di-lithiated polyisoprene (PI) chains with 1,2-isopropylidene glyceryl glycidyl ether (IGG) and subsequent acidic deprotection. The resulting hexa-hydroxy functional PI-macroinitiators were then used to initiate L-lactide (LLA) in a DBU-catalysed polymerisation, ultimately yielding super-H-shaped (PLLA)3-b-PI-b-(PLLA)3 triblock structures with molecular weights of 23–49 kg mol−1. Narrow molecular weight distributions with dispersity in the range of 1.19–1.35 were obtained, and thermal characterisation revealed two distinct glass transition temperatures (Tg), indicating phase separation. The PI-domains feature a low Tg between −55 °C and −59 °C, whereas the PLLA-domains exhibit a higher Tg of 41 °C to 49 °C. Further, the block copolymers were analyzed by TEM and SAXS, confirming clearly phase-separated cylindrical and lamellar morphologies. The reported bifunctional approach combining carbanionic polymerization with the ROP of lactones represents an efficient and general synthesis pathway for a large variety of complex polymer architectures.

In plants, the topological organization of membranes has mainly been attributed to the cell wall and the cytoskeleton. Additionally, few proteins, such as plant-specific remorins have been shown to function as protein and lipid organizers. Root nodule symbiosis requires continuous membrane re-arrangements, with bacteria being finally released from infection threads into membrane-confined symbiosomes. We found that mutations in the symbiosis-specific SYMREM1 gene result in highly disorganized perimicrobial membranes. AlphaFold modelling and biochemical analyses reveal that SYMREM1 oligomerizes into antiparallel dimers and may form a higher-order membrane scaffolding structure. This was experimentally confirmed when expressing this and other remorins in wall-less protoplasts is sufficient where they significantly alter and stabilize de novo membrane topologies ranging from membrane blebs to long membrane tubes with a central actin filament. Reciprocally, mechanically induced membrane indentations were equally stabilized by SYMREM1. Taken together we describe a plant-specific mechanism that allows the stabilization of large-scale membrane conformations independent of the cell wall. © 2023, The Author(s).

Within the present work, a thermo-responsive ultrafiltration membrane is manufactured based on a polystyrene-block-poly(diethyl acrylamide) block copolymer (BCP). The poly(diethyl acrylamide) block segment features a lower critical solution temperature (LCST) in water, similar to the well-known poly(N-isopropylacrylamide), but having increased biocompatibility and without exhibiting a hysteresis of the thermally induced switching behavior. The BCP is synthesized via sequential “living” anionic polymerization protocols and analyzed by 1H-NMR spectroscopy, size exclusion chromatography, and differential scanning calorimetry. The resulting morphology in the bulk state is investigated by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) revealing the intended hexagonal cylindrical morphology. The BCPs form micelles in a binary mixture of tetrahydrofuran and dimethylformamide, where BCP composition and solvent affinities are discussed in light of the expected structure of these micelles and the resulting BCP membrane formation. The membranes are manufactured using the non-solvent induced phase separation (NIPS) process and are characterized via scanning electron microscopy (SEM) and water permeation measurements. The latter are carried out at room temperature and at 50 °C revealing up to a 23-fold increase of the permeance, when crossing the LCST of the poly(diethyl acrylamide) block segment in water.

It is commonly observed that voids can nucleate and grow in the lithium anode of a solid state Li-ion battery at a location adjacent to the solid electrolyte during the stripping (discharge) phase of the battery; a similar phenomenon is observed in sodium-based batteries. It is hypothesised in the current literature that the formation of these voids is due to the coalescence of vacancies that have been generated at the electrode/electrolyte interface when metal atoms are oxidized and transported into the electrolyte: the slow diffusion of the vacancies away from the electrolyte interface into the adjacent electrode results in their coalescence and the consequent growth of voids. These hypotheses are challenged in the current study by using the Onsager formalism to generate a variational principle for vacancy diffusion. Our analysis reveals that no driving force exists for the diffusion of vacancies into a homogeneous metal electrode that thins by stripping. This finding is contrary to models in the literature which have mistakenly assumed that the vanishing flux at the current collector prevents rigid body motion (drift) of the electrode which in turn prevents thinning of the electrode during stripping. Based on our analysis, we conclude that vacancy diffusion within a homogeneous electrode is not responsible for the nucleation and growth of voids at the interface between a stripping metal electrode and a solid electrolyte.

Recently, carbon spherogels have been introduced as a novel monolithic aerogel composed of hollow spheres. This material is conveniently obtained via polystyrene (PS) sphere templating. In the present study, we apply a water-soluble titania precursor (titanium(IV) bis(ammonium lactate) to the aqueous sol-gel synthesis based on resorcinol-formaldehyde (RF) to effectively encapsulate titania. In this way, a very high mass loading of up to 59 mass% of titania can be confined strictly to the inside of the hollow carbon spheres. In the final synthesis step, carbonization at 800 °C has three simultaneous effects: Transformation of the RF coating on PS into microporous carbon, PS template removal by decomposition, and formation of titania due to precursor dissociation. A deliberate tuning of the microporous carbon shell, accessibility of the titania, titania amount, and titania's polymorph is further demonstrated by thermal treatment under a carbon dioxide atmosphere. In contrast to non-tuned or TiC-containing carbon spherogels, CO2 activation of the composites results in a three orders of magnitude rise of their photocatalytic activity towards hydrogen evolution reaction, which we evaluate using flow and batch reactors. We further show that this effect is related to the partial etching of the carbon shell, which renders the TiO2 surface accessible to the reactants in the solution and allows for an efficient hole scavenging. Given the simplicity of the hybrid carbon spherogel (HCS) composite fabrication, the high degree of control of their morphological characteristics, and the striking effects of CO2-activation on performance, we believe that our results will contribute to the development of similar carbon-inorganic composites.