Vortrag  |  Kolloquien  |  Physik  |  Chemie

Playing with Order and Disorder in Hydrogen-Bonded Supramolecular Materials

Wann
Donnerstag, 05. Dezember 2019
17:00 – 18:00 Uhr

Wo
A704

Veranstalter
Stefan Mecking

ReferentIn:
Holger Frauenrath, EPF Lausanne, CH

Abstract:

Nature does not only accept the inevitable presence of disorder in structural materials but even plays with it. Biological systems use specific supramolecular interactions to control the placement of disorder on some length scales, use disorder to create structures on others, and implements structural gradients between ordered and disordered domains to fine-tune mechanical properties. We attempt to implement similar concepts in in order to tailor electronic, dynamic, or thermomechanical properties across different classes of supramolecular materials.

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 observed the reversible photogeneration of 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 fundamental concepts, we 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 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.

Co-assembling oligopeptide-modified thermoplastic polymers with low-molecular weight additives based on the same self-assembling segment has allowed us to tailor the oligopeptide aggregation independently of the polymer molecular weight. This approach therefore gives rise to thermoplastic materials comprising a network of one-dimensional supramolecular aggregates even at molecular weights well above the entanglement molecular weight. Independent of the employed type of polymer, the resulting materials show remarkable combinations of stiffness, strength, ductility and toughness at room temperature, a novel rubbery plateau and an unusual melt elasticity above the polymer melting point, and therefore offer new processing options.