Structurally important biological materials generically show hierarchical structures to allow functional properties. They exploit self-assemblies over the length scales by competing interactions and combining tailored supramolecular interactions. Examples are provided by spider silk, nacre, and bone, which show extraordinary mechanical properties, regardless of the weak individual building blocks. In these materials, the strength and toughness arise from nanoscale toughening mechanisms, where hard and soft domains are connected covalently and by weak interactions. They work in synergy to transfer stress from bulk to the reinforcing parts via sacrificial bonds and hidden lengths through hierarchical design. In this thesis, an overview of the important aspects in biomimetic material design, such as supramolecular chemistry, self-assembly, hierarchical structures, and sacrificial bonding is first given. In the later chapters, four articles and their important findings towards novel biomimetic materials are highlighted. In the publications I and II, self-assemblies of asymmetric bile acid -based amphiphilic polymers were studied. The results suggest designing complex amphiphilic self-assembling systems to create hierarchical materials from nanoscale to bulk upon "switching-on" supramolecular interactions. In the publication III, a nanocomposite between multi-walled carbon nanotubes and a polymer was synthesized. The adhesion between the polymer and the carbon nanotubes was supramolecularly enhanced to control their relative slipping. Due to supramolecular reinforcements and hierarchical structure, the resulting nanocomposite showed slow crack propagation upon fracturing, reminiscent of natural materials. In the publication IV, well-defined oligomeric oligosaccharide-based molecules with end-groups capable of supramolecular hydrogen bonds were studied. Polarized optical microscopy suggested columnar liquid crystallinity in a specific hydrogen bonding solvent medium and upon complete solvent removal hydrogen bonds between the oligosaccharides were formed allowing supramolecular polymers and fiber spinning. This work paves ways to understand switching-on of hydrogen bonds "on-demand" in the processing, mimicking silk-spinning. In summary, the present work shows ways to incorporate supramolecular interactions of different strengths for functional materials, inspired by biological materials.
|Translated title of the contribution||Biomimeettiset supramolekulaariset rakenteet|
|Publication status||Published - 2018|
|MoE publication type||G5 Doctoral dissertation (article)|
- supramolecular chemistry