Bio-inspired Assembly Of Nanoscale Building Blocks For Preparation Of Layered Nanocomposites And Their Properties

Materials scientists have been devoting their efforts to fabricate various high-performance functional materials to meet the demands of society. In contrast to synthetic materials, evolutionary developments in biology have resulted in strong materials with remarkable structural properties, made out of relatively weak constituents, arranged in complex hierarchical patterns. These biological materials are typically multifunctional. Therefore, rigid biological systems are increasingly becoming a source of inspiration for the fabrication of next generation advanced functional materials due to their diverse hierarchical structures and remarkable engineering properties. Among these rigid biomaterials, nacre, as the main constituent of the armor system of seashells, exhibiting a well-defined ’brick-and-mortar’ architecture, excellent mechanical properties, and interesting iridescence, has become one of the most attractive models for novel artificial materials design.In this dissertation, we focus our research interest on this interesting model. Firstly, we overviewed the relationship between the hierarchical structures and the properties of nacre, and summarized the principles of fabrication of artificial nacre based on this model. Then, we used proper nanoscale building blocks and systems, designed and adopted suitable assembly techniques, successfully fabricated several well-ordered hybrid nanocomposites. Their properties have been well investigated as well. The main achievements can be summarized as follows:1. Ultrathin hybrid films have been fabricated from nanometer scale ionic clusters and proteins using layer-by-layer (LBL) assembly method. The cluster-protein hybrid films exhibited structural homogeneity, relative transparency, and bright blue fluorescence. More importantly, these hybrid films displayed up to a 70% increase in hardness and up to a 100% increase in reduced Young’s modulus compared to the pure BSA film. Interestingly, the reinforcement effects of clusters are related to their inherent structures and interactions with proteins. These hybrid cluster-protein films could be potentially used as biomedical coatings in future because of their good transparency and excellent mechanical properties.2. Strong, colorful, and fire retardant coatings can be constructed based on nacre-inspired layered structures by using graphene oxide (GO) nanosheets and layered double hydroxides (LDHs) nanoplatelets as building blocks via layer-by-layer assembly. Such all-inorganic GO-LDH hybrid coatings show uniform nacre-like layered structures that endow them good mechanic properties with Young’s modulus of～18 GPa and hardness of-0.68 GPa. In addition, the GO-LDH hybrid coatings exhibit nacre-like iridescence and attractive flame retardancy as well due to their well-defined two dimensional microstructures. This kind of nacre-inspired all inorganic GO-LDH hybrid coatings will be alternatives for functional coatings in future due to their low cost, high strength, and multi-functionalities.3. Artificial nacre-like organic-inorganic hybrid films with’brick and mortar’ microstructures have been fabricated based on clay, chitosan and cellulose nanofibers. The hybrid films show high mechanical performances and reproduce the architectures of nacre. Based on the previous investigation of clay and chitosan nanocomposites, we successfully introduced one-dimension cellulose nanofibers into the previous binary hybrid system and carefully studied the effect of cellulose nanofibers on the mechanical performances of the resulting ternary artificial nacres. The results show that with a right amount of content of cellulose nanofibers, the films exhibit enhanced mechanical properties including strength, toughness and hardness compared with the binary hybrid films.4. CoGe03(en)o.s hybrid nanowires have been synthesized in a binary ethylenediamine/H2O solvent system via a solvothermal process and used as templates to prepare CoGeO3 nanowires. The optical and magnetic properties of CoGe03(en)o.5 hybrid nanowire are totally different from pure inorganic CoGe03 due to intercalation of en molecules. The as-obtained CoGe03(en)o.5 hybrid nanowires were used as efficient precursors for CoGeO3 nanowires with a simple thermal decomposition process. Furthermore, the electrochemical and electrocatalytic properties for the oxygen reduction reaction (ORR) of the obtained CoGeO3 nanowires have been studied and show attractive electrochemical supercapacitance and electrocatalytic activities, indicating their potential applications as supercapacitors and electrochemcial catalysts.