Hierarchical composites by gluing of nano- and mesocrystals

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In natural organic inorganic composites such as bone or nacre, stiff and very brittle mineral crystals are joined by soft organic materials. Due to a sophisticated hierarchical structuring and a well controlled coupling at the interface between the two components, these biological structures combine both stiffness and toughness. By means of arranging inorganic crystals with the help of organic molecules, natural biocomposites also achieve remarkable optical and magnetic properties. Inspired by these concepts, we manufacture biomimetic composite structures by gluing together mineral particles with polymers and hierarchical structuring by one step self organization via liquid crystal formation.The polymers used are copolymers with cholesteryl LC side chains or helical backbones carrying amino acid (carboxyl/amino) gluing units (various LC/gluing unit ratios and chain lengths). The polymers form chiral nematic lyotropic phases on the µm length scale, and the carboxyl groups of the polymer side chains act as gluing units by binding to the nanoparticle faces via Coulomb interaction or hydrogen bonding. Two hierarchical level composite bulk samples with anisotropic nanocrystals (Laponite clay platelets and vanadium pentoxide nanoparticles) and LC polymer are produced via one step self organization: alignment of nanoparticles (first level) within a structured organic matrix (second level). Different analytical techniques (light microscopy, micro tomography, SEM, SAXS, and TEM) revealed the hierarchical structuring of Laponite and vanadium pentoxide composite materials from the mm and µm lengthscale to the nm lengthscale. Mechanical characterization by nanoindentation supported the observed structural anisotropy.This approach allows for systematic variation of structures and for optimizing the mechanical performance as well as investigating the effects of the hierarchical structuring on the mechanical properties (structure property relationship). In addition, our objective is the fabrication of multifunctional composite materials with optimized mechanical as well as optical/magnetic properties, finally aiming at investigating the influence of the hierarchical structuring on the final material properties. To this end, hierarchically structured composite materials with other technologically relevant and abundant materials like gold nanorods and magnetic nanoparticles will be synthesized by applying our structuration concepts. Furthermore, by using magnetic nanoparticles, the nanoparticle alignment can be optimized by means of an external magnetic field, potentially enabling nanoparticle orientation up to the macroscopic scale.