@article{EckertRudolphGuoetal.2018, author = {Eckert, Alexander and Rudolph, Tobias and Guo, Jiaqi and Mang, Thomas and Walther, Andreas}, title = {Exceptionally Ductile and Tough Biomimetic Artificial Nacre with Gas Barrier Function}, series = {Advanced Materials}, volume = {30}, journal = {Advanced Materials}, number = {32}, publisher = {Wiley-VCH}, doi = {10.1002/adma.201802477}, pages = {Article number 1802477}, year = {2018}, abstract = {Synthetic mimics of natural high-performance structural materials have shown great and partly unforeseen opportunities for the design of multifunctional materials. For nacre-mimetic nanocomposites, it has remained extraordinarily challenging to make ductile materials with high stretchability at high fractions of reinforcements, which is however of crucial importance for flexible barrier materials. Here, highly ductile and tough nacre-mimetic nanocomposites are presented, by implementing weak, but many hydrogen bonds in a ternary nacre-mimetic system consisting of two polymers (poly(vinyl amine) and poly(vinyl alcohol)) and natural nanoclay (montmorillonite) to provide efficient energy dissipation and slippage at high nanoclay content (50 wt\%). Tailored interactions enable exceptional combinations of ductility (close to 50\% strain) and toughness (up to 27.5 MJ m⁻³). Extensive stress whitening, a clear sign of high internal dynamics at high internal cohesion, can be observed during mechanical deformation, and the materials can be folded like paper into origami planes without fracture. Overall, the new levels of ductility and toughness are unprecedented in highly reinforced bioinspired nanocomposites and are of critical importance to future applications, e.g., as barrier materials needed for encapsulation and as a printing substrate for flexible organic electronics.}, language = {en} } @article{EckertAbbasiMangetal.2020, author = {Eckert, Alexander and Abbasi, Mozhdeh and Mang, Thomas and Saalw{\"a}chter, Kay and Walther, Andreas}, title = {Structure, Mechanical Properties, and Dynamics of Polyethylenoxide/Nanoclay Nacre-Mimetic Nanocomposites}, series = {Macromolecules}, volume = {53}, journal = {Macromolecules}, number = {5}, publisher = {ACS Publications}, address = {Washington, DC}, issn = {1520-5835}, doi = {10.1021/acs.macromol.9b01931}, pages = {1716 -- 1725}, year = {2020}, abstract = {Nacre-mimetic nanocomposites based on high fractions of synthetic high-aspect-ratio nanoclays in combination with polymers are continuously pushing boundaries for advanced material properties, such as high barrier against oxygen, extraordinary mechanical behavior, fire shielding, and glass-like transparency. Additionally, they provide interesting model systems to study polymers under nanoconfinement due to the well-defined layered nanocomposite arrangement. Although the general behavior in terms of forming such layered nanocomposite materials using evaporative self-assembly and controlling the nanoclay gallery spacing by the nanoclay/polymer ratio is understood, some combinations of polymer matrices and nanoclay reinforcement do not comply with the established models. Here, we demonstrate a thorough characterization and analysis of such an unusual polymer/nanoclay pair that falls outside of the general behavior. Poly(ethylene oxide) (PEO) and sodium fluorohectorite form nacre-mimetic, lamellar nanocomposites that are completely transparent and show high mechanical stiffness and high gas barrier, but there is only limited expansion of the nanoclay gallery spacing when adding increasing amounts of polymer. This behavior is maintained for molecular weights of PEO varied over four orders of magnitude and can be traced back to depletion forces. By careful investigation via X-ray diffraction and proton low-resolution solid-state NMR, we are able to quantify the amount of mobile and immobilized polymer species in between the nanoclay galleries and around proposed tactoid stacks embedded in a PEO matrix. We further elucidate the unusual confined polymer dynamics, indicating a relevant role of specific surface interactions.}, language = {en} }