Structure and spatially resolved mechanics as well as rheology of near-surface regions of adaptive polymer networks

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The aim is to design reactive coatings of amphiphilic co-networks (ACN) that are sensitive to external stimuli such as solvent composition (hydrophilic/hydrophobic balance), pH, temperature and light. To this end, a deep understanding and thus rational control of the relationship between structure, swellability and mechanics/rheology in the near-surface region of ACN will be achieved at nanoscopic and microscopic levels. Both covalently and ionically-reversibly linked ACNs will continue to be used, whose building blocks are 4-armed stars and which will be synthesised in TP1 and TP2, respectively. In addition, the variety of compounds will be expanded in the second funding period with regard to hybrid networks. On the one hand, covalent-reversible networks will be investigated, and on the other hand, covalent-electrostatic networks will be constructed in which one part of the tetra-stars is linked covalently and the other part ionically-reversibly (TP2). In addition, the tetra-armed stars are to partially contain thermosensitive polymer components (TP2) that reversibly collapse or swell in response to temperature variation in the solvent. In addition, rapid switching by external fields such as light should be possible. For this purpose, gold nanoparticles (AuNP) are to be added to the gel, which rapidly collapse or swell temperature-sensitive areas in the gel by plasmonic heating. A suitable preparation technique must be found for each system. For structural investigations in the near-surface area, atomic force microscopy is still the main method. Here, both the surface topography is determined with high spatial resolution and the mechanical and rheological properties are investigated by indentation experiments with variation of the external stimuli. In addition to atomic force microscopy, GISAXS and GISANS measurements will also help to elucidate the structure in the near-surface region. The structural information obtained in the near-surface regions will be compared with that of the bulk phase (SAXS) from TP3. In TP6, pattern formation by phase separation is simulated. From this, correlation lengths of the pattern formation can be determined and compared with the AFM experiments. TP 5 will clarify how the mechanics/rheology on macroscopic length scales (TP4) is composed of the mechanical properties on small length scales (10 nm to 10 micrometer). With TP 7, experimentally determined and theoretically predicted E-moduli are to be compared. In collaboration with TP8, it will be investigated whether quasi-2D networks can be produced that are suitable as cell-compatible and possibly reactive coatings for biomedical applications.