6 Materialchemie
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The 2-methoxyphenol units (G-units) in lignin are modified by demethylation and oxidation to provide the activated lignin as one part of an advanced biobased two-component (2K) adhesive system, which exhibits promising shear strengths in dry and underwater applications. The activation of lignin is straightforward and generates quinones via demethylation and periodate oxidation. These act as Michael acceptors and react smoothly with multi-thiol-star polymers to yield thiol-catechol connectivities (TCCs). The mussel-inspired material platform acts as a very robust and versatile adhesive, combining low-cost and readily available lignin with multi-thiols to achieve outstanding adhesion strengths of up to 15 MPa in dry application. In particular, the 2K system is compatible with the marine biological environment and shows no acute toxicity to sensitive organisms such as fish eggs. Thus, one possible application of this material could be an adhesive for setting temperature-resistant corals in damaged reefs.
ABX3 metal halide perovskites revolutionized the research and development of new optoelectronics, including solar cells and light-emitting diodes. Processing polycrystalline thin films from precursor solutions is one of the core advantages of these materials since it enables versatile and cost-effective manufacturing. The perovskite film morphology, that is, continuous substrate coverage and low surface roughness, is of paramount importance for highly efficient solar cells and optoelectronic devices in general. Controlling the chemistry of precursor solutions is one of the most effective strategies to manage the perovskite film morphology. Herein, we show the fundamental influence of the A-site cation composition on the perovskite precursor arrangement and the consequent film formation. Extended X-ray absorption fine structure spectroscopy and small-angle X-ray scattering give unprecedented insights into the complex structural chemistry of the perovskite precursors and, in particular, their repulsive interactions as a crucial parameter for colloidal stability. Combining these techniques with in situ grazing incidence wide-angle X-ray scattering during thin-film formation allows us to identify the mechanism for using alkali metals as a decisive criterion to control the colloidal stability of the perovskite precursor and thus the thin-film morphology. We illustrate the fundamental principle behind the systematic use of alkali metals regardless of whether they are incorporated in the lattice or not. Hence, this work provides tools to selectively control the morphology and crystal growth in present and future systems