Hierarchical composites by gluing of nano- and mesocrystals

在天然有机无机复合材料中，如骨或珍珠层，坚硬和非常脆的矿物晶体被软的有机材料连接在一起。由于复杂的层次结构和在两个组件之间的界面处良好控制的耦合，这些生物结构结合了刚性和韧性。通过在有机分子的帮助下排列无机晶体，天然生物复合材料也具有显著的光学和磁学性能。在这些概念的启发下，我们通过将矿物颗粒与聚合物粘合在一起，并通过液晶形成一步自组织形成层次化结构来制造仿生复合材料结构。所使用的聚合物是带有胆固醇基LC侧链的共聚物或带有氨基酸(羧基/氨基)胶合单元(不同LC/胶合单元比和链长)的螺旋骨架的共聚物。聚合物在微米尺度上形成手性向列型溶致变性相，聚合物侧链上的羧基通过库仑相互作用或氢键与纳米粒子表面结合，作为胶合单元。通过一步自组织：纳米颗粒(第一层)在结构有机基质(第二层)中的排列，制备了两个具有各向异性纳米晶(滑石粉、粘土小片和五氧化二钒纳米颗粒)和液晶聚合物的分级级复合块体样品。不同的分析技术(光学显微镜、显微断层扫描、扫描电子显微镜、小角X射线衍射仪和透射电子显微镜)揭示了从毫米和微米尺度到纳米尺度的层次化结构。纳米压痕的力学表征支持观察到的结构各向异性。这种方法允许系统地改变结构，优化机械性能，以及研究分级结构对力学性能(结构性能关系)的影响。此外，我们的目标是制备具有优化的力学和光学/磁学性能的多功能复合材料，最终目的是研究层次化结构对最终材料性能的影响。为此，我们将应用我们的结构化概念，与其他技术相关和丰富的材料，如金纳米棒和磁性纳米颗粒，合成具有层次结构的复合材料。此外，通过使用磁性纳米颗粒，可以通过外部磁场来优化纳米颗粒的排列，潜在地使纳米颗粒的取向达到宏观范围。

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.