Fabrication Of Bio-Inspired Structured Functional Composites Via Hierarchical Assembly Of Micro-/Nano-Building Blocks

In the past decades, various nanostructured materials have been synthesized via mature techniques. However, the currently emerging challenge is that how to efficiently utilize these novel functional nanomaterials in practical fields. The assembly of functional nano-building blocks into macroscale bulk materials within hierarchical micro-/nano- structures via advantaged fabrication techniques is a feasile route to broaden the practical applications of nanostructured materials. By hierarchical assembly of nano-building blocks, the obtained bulk materials not only own the properties of nano-building blocks but also behave the synergetic properties and multifunctionalities due to the hierarchical organizations. One the other hand, the research on bio-inspired hierarchical structures indicates that mimicking the?biological hierarchical structure in artificial material can enhance and optimize the property and functionality. For the design and fabrication of hierarchical structures, nature offers us much inspiration and many models. For example, the“brick and mortar”structured nacre, the bone’s“nanofiber consisted plate”structure, wood’s“cellular”structure, the“nanobelt assembled plate”structure of pistachio’s shell and cactus’s spicule, sponges’s“three dimensional network”structure, and so on.The present dissertation will focus on the fabrication of bio-inspired hierarchical structured functional composite materials based on the models of biomaterials and ordered assembly of artificially synthesized functional micro-/nano- building blocks. According to the components and structures analysis of biomaterials, we firstly searched and designed proper artificial building blocks. Then, we synthesized these artificial building blocks on large scale, such as one dimensional nano fibrious materials and two dimensional platelet-like or sheet-like nanomaterials. Finally, we assembled these artificial inorganic building blocks together with polymers to fabricate bio-inspired structural functional composite materials. The excellent mechanical propeties, special optical and electric properties, and their multifunctionalities have been studied. The main results can be summarized as follows:1. Biologically inspired, strong, transparent, and functional layered double hydroxides (LDHs) or zeolites micro-bricks reinforced composite films have been successfully fabricated. In this work, according to the model of layered structure of nacre, we firstly synthesized the platelet-like LDHs or zeolites microcrystals on large scale. Then, by using these LDHs or zeoites platelet-like microcrystals as inorganic building blocks, a series of strong, transparent, functional nacre-like layered hybrid films were fabricated via interfacial assembly and layer by layer spin coating technique. The obtained hybrid films displayed nacre-like layered microstructures and behaved excellent tensile strength which is comparable to that of natural nacre. Interestingly, these hybrid films are transparent and their optical properties can be tuned by using different inorganic functional building blocks.2. Artificial nacre-like chitosan-Montmorillonite (MTM) bionanocomposite films with amazing‘brick and mortar’microstructures have been fabricated based on using chitosan-MTM hybrid nanosheets as building blocks. In the designed fabrication procedure, we assembled hybrid building blocks with thin layer of chitosan coating on the MTM nanosheets to form chitosan-MTM bionanocomposite film via vacuum filtration or water evaporation. The obtained nacre-like films displayed higher performance in mechanical properties (Young’s modulus: 10 GPa, tensile strength: 100 MPa) compared with the film made by conventional method. Moreover, these hybrid films are transparent and fire-retardant. Addtionally, gold nanoparticles (Au NPs) can be modified on the surfaces of chitosan-MTM hybrid nanosheets via in situ growth method. The obtained chitosan-MTM-Au NPs hybrid building blocks can also been assembled to form nacre-like layer structured films with good tensile strength and novle optical properties expanding the applications of nacre-like chitosan-MTM hybrid films.3. Based on the ultrafine two dimensional structure of graphene oxide, we designed and fabricated a series of nacre-like layer structured reduced graphene oxide-ceramic nanocomposite films and bulk bricks: (1) By using graphene oxide (GO) and titania oxide (TiO) nanosheets as functional building blocks, high quality (PDDA/GO/PDDA/TiO)20 hybrid films were fabricated on the glass substrate through alternatively LBL self-assembly with GO, TiO nanosheets, and PDDA. Then, the photoconductive pattern was fabricated by illuminating the hybrid film equipped with a pre-designed aluminum foil as the shadow mask through the photothermal and photocatalyic reduction; (2) The graphene oxide nanosheets were firstly coated with mesoporous silicon precursor to form the GO-mesoporous silicon precursor hybrid nanosheets. Then, these obtained GO-mesoporous silicon precursor hybrid nanosheets were hot pressed together to yield a bulk brick which consisted of lamellar RGO connected by mesoporous silicon. The bulk brick is light weight, robust, and conductive due to its hierarchial structures.4. Elastomeric conductors composed of sponge-like three dimensional silver-carbon hybrid nanocable/carbon nanotube networks have been fabricated by using hydrothermal synthesized Ag@PVA nanocables networks as templates. Sponge-like materials, composed of interconnected one dimensional nanostructures, have attracted intensive attention of researchers due to their high porosity, high surface area, light-weight, and excellent mechanical strength. By carefully controlling the conditions of hydrothermal reaction, we firstly demonstrated that the silver@PVA nanocables can grow and interconnect each other to form the cylinder-shaped three dimensional networks. Through carbonization of silver@PVA nanocable networks, the conductive silver-carbon hybrid nanocable/nanotube sponges can be fabricated as elastomeric conductors, which show good compressive properties and high conductivties (1.28 S·m-1), and good reversibility. Moreover, these artificial sponges can also be used to fabricate the conductive nanocomposites due to their percolating three-dimensional network nanostrucutres.5. As a feasible route to synthesize various nanostructured materials, the small organic amine templating synthesis of organic-inorganic hybrid nanostructured materials has been further developed. The obtained hybrid nanostructured materials can be also used as efficient precursors to synthesize functional inorganic nanomaterials. We synthesized a new kind of blue light emitting ultralong Cd(L)(TeO3) (L = ethylenediamine, diethylenetriamine) nanofibre bundles and studies their thermal and acidic stabilities; prepared uniform, well-defined, and platelet-like hydrazine-cadmium tellurite hybrid microcrystals and used them as precursors to yield porous cadmium telluride and tellurium architectures; synthesized the Cd2Se2(pa) hybrid materials and used them as a precursor to explore the“top-down”fabrication process of structural evolution from two dimensional layered structures to zero- or one- dimensional nanocrystals. These functional nanostructured materials are also promising to be used as building blocks in the fabrication of bio-inspired hierarchical structured materials.