| To meet the imperious demands in and high-tech industry, advanced functional materials with enhanced mechanical performance based on the structural optimization design becomes a hot research topic in material science area. Many natural biomaterials including bone, nacre and bamboo display excellent mechanical performance. Owing to well development of characterization, the relationship between macroscopic performance and microscopic structure of natural structural materials has attracted great attentions in recent years. As a well-known example, nacre not only displays excellent mechanical properties and interesting iridescence, but also possesses a well-defined 'brick-and-mortar' architecture, so it is considered as a popular bioinspired model for the design of high strength and toughness functional materials. In this thesis, we choose nacre and other layered structural materials in nature as templates, and select varying nanosized wires and sheets as building units. With these building blocks, we successfully fabricated a series of bioinspired layered composite films via a facile spraying mediated assembly process. In addition, the relationship between mechanical performance and microstructure of these bioinspired composite films has been further investigated. The main achievements can be summarized as follows:(1) Ag NWs and thiolate chitosan (TCS) were selected as building blocks. A series of bioinspired Ag NWs reinforced TCS composite films have been successfully constructed by spraying mediated layer-by-layer assembly process.The introduction of Ag-S covalent bonds is confirmed herein to enhance the interfacial interaction, and further significantly reinforce these composite films.The mechanical property of the final composite film with the optimal Ag NWs proportion (60%) was greatly enhanced through this strategy. The tensile strength and Young's modulus can be enhanced up to 11.7 and 3.9 times of pure TCS, which is also superior to that of 60% Ag NW-chitosan (CS) film, bulk metallic silver, typical nanocrystal-CS and other Ag NW-polymer composite films. Furthermore, this Ag NW-TCS composite film possesses excellent fatigue resistance. This Ag-S covalent bonds mediated reinforcement may help to fabricate more high-performance composites.(2) Due to excellent mechanical performance, high-temperature tolerance and chemical inertness, aramid fiber is an important high-performance composite material, which has been widely employed in aerospace, vessel and protective gear. As reported recently, aramid fibers could be successfully exfoliated into nanofibers in a large scale, which serve as a novel building block for the assembly of macroscopic structural materials. Herein, we integrate 1-D aramid nanofibers and 2-D mica sheets into a series of mica-aramid nanofiber composite films using spraying mediated layer-by-layer assembly. Both the multilayered structure and abundant hydrogen bonds at the interface between mica sheets and aramid nanofibers significantly improve mechanical properties of composite films. When the inorganic component reaches 40 wt%, the tensile strength, modulus, and toughness of the optimized composite film are enhanced 1.7, 3.2 and 1.8 times compared with that of the pure aramid nanofiber film,respectively, and this composite film exhibits well flexibility and visible transparence.(3) A series of nacre-mimic composite films had been successfully constructed based on mica nanosheets and sodium alginate (SA) via a spraying mediated self-assembly. Due to the electrostatic attraction and hydrogen bonding between mica nanosheets and SA, both the strength and modulus of the optimum mica nanosheets-SA film reach up to 205 MPa and 18.4 GPa, respectively. This optimized composite film displayed well visible transmission and fire-retardance. Furthermore, polyethylene terephthalate (PET) substrate film could be coated by this composite layer to realize the functional modification. |
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