Playing with Order and Disorder in Hydrogen-Bonded Supramolecular Materials

Prof. Dr. Holger Frauenrath , Ecole Polytechnique Federale de Lausanne (EPFL)
Nature does not only accept the inevitable presence of disorder in structural materials but even plays with it: it uses highly specific supramolecular interactions to control the placement of disorder on some length scales, uses it to create structures on others, and implements structural gradients between ordered and disordered domains to guide external fields. We attempt to implement similar concepts in in order to tailor electronic, dynamic, or thermomechanical properties across different classes of supramolecular materials. For example, we obtained well-defined helical supramolecular polymers from oligopeptide-substituted organic semiconductors. Synergistic hydrogen-bonding of the oligopeptide substituents and π–π stacking, and the formation of isolated stacks of the chromophores resulted in strong electronic coupling and charge transport properties not observed in related materials with higher degree of order. We bserved reversible photogeneration of polaron charge carriers at high concentrations and with unusual lifetimes of several hours in these supramolecular polymers, without the addition of any redox-active reagent. Using the same basic concepts, we also prepared novel supramolecular elastomers based on oligopeptide-modified polymers. Self-assembly of the oligopeptides into one- dimensional aggregates gives rise to a network of nanofibrils that serve to reinforce the resulting elastomers, which show excellent elastic properties, high stiffness, and sharp melting transitions at high melting temperatures. Blending different oligopeptide- modified polymers, on the other hand, results in “interpenetrating supramolecular networks” by self-sorting self-assembly. In such hierarchically structured materials, the various topologically independent supramolecular networks undergo distinct frequency- dependent rheological solid-fluid transitions, which results in high performance damping materials with high stiffness. Finally, we also used oligopeptide-modified polymers to obtain thermoplastic materials comprising a network of one-dimensional supramolecular aggregates. The resulting materials show remarkable combinations of stiffness, strength, ductility and toughness at room temperature, as well as a greater selection of processing options.
Colloquium on Advanced Materials
9 May 2019, 17:00
Centre for Advanced Materials, INF 225, 01.413

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