Study On The Fabrications And Properties Of The Artificial Nacre-mimic Composite Films With Hierarchical Structure

This dissertation focuses on the fabrications and mechanical properties of the nacre-like hierarchical structured composite films for discovering the inner relationships between the hierarchical structures and excellent performances.Combination of the recent fabrication methods, study progresses and developmental tendencies about the assembled hierarchical layer structured materials, we assembled the unary, binary and ternary nacre-like hierarchical structured composite films based on the affinity recognition interactions between the organic matrixes and the building blocks, and the synergistic toughening among building blocks. Different building blocks such as Graphene oxide, Clay nanosheets, Aragonite planets, and Nanofibrillar xonotlite were used for constructing the nacre-like hierarchical structured composite films. Further, we investigated the fabrication mechanisms of the nacre-like hierarchical structured composite films and their mechanical performances. The main results of this study can be summarized as follows:1. A facile and novel method is reported for large-scale preparation of highly dispersed and dense Ag NPs on flexible rGO paper. Through the self-polymerization of dopamine, the free-standing GO paper is simultaneously reduced and modified with following in-situ growth of monolayer Ag NPs on the substrate. The surfaced spherical Ag NPs with an average diameter of 80 nm present a narrow size distribution and a high cover dense. The cover dense of Ag NPs on the rGO paper decreased with reducing the concentration of Ag+ ions. Importantly, the flexible rGO/Ag hybrid paper presents a high active/sensitive SERS response toward R6G molecules, the detection signals can be obtained while the R6G concentration is as low as to 10-8M. This work provides a simple strategy for large-scale fabrication of monolayer Ag NPs as SERS platform with broad potential applications.2. Nacre-like hierarchical structured composite films were successfully assembled by using sticky rice soup-Montmorillonite ?SRS/MTM? hybrid nanosheets as building blocks via vacuum filtration or water evaporation, in which the organic matrix in SRS act as "mortar" and MTM nanosheets play the role of "brick". The obtained binary nacre-like composite films display higher performances in mechanical properties through water evaporation (tensile strength: 126.6±5.1 MPa,Young's modulus: 9.0 ±0.3 GPa,toughness: 1.81 ± 0.1 MJ m^-3) compared with the film made by vacuum filtration (tensile strength: 103.9 ± 3.5 MPa,Young's modulus: 5.9 ±0.15 GPa,toughness: 1.17 ± 0.08 MJ m^-3). Denser layer structure and higher matrix fraction might arouse the difference of mechanical performances of the binary composite films.Moreover, the mechanical properties of the binary composite film made by water evaporation are similar to that of nature nacre (tensile strength: 80^-135 MPa, and toughness: 1.8 MJ m^-3 ). However, the artificial composite films show more excellent flexible characters. Such fabrication protocols provide a simple, facile and inexpensive method to large-scale fabricate nacre-like hierarchical structured composite films for potential applications.3. Montmorillonite/poly?vinyl alcohol?/nanofibrillar xonotlite ?MTM/PVA/NFX?ternary composite films with nacre-like architecture are assembled by simple vacuum filtration technique. The lamellar architecture is alternately stacked by one-dimensional ?1D? NFX network layer and two-dimensional ?2D? MTM nanosheet layer with an adjustable interlayer distance. Importantly, the typical artificial MTM/PVA/NFX ternary composite film shows a perfect combination of high strength?241.8 ±10.2 MPa? and toughness (5.85 ± 0.46 MJ m^-3),many times higher than that of the unitary NFX network film and the binary MTM/PVA composite film, and superior to nature nacre and most conventional MTM/polymer binary composite films.Such excellent mechanical properties of the artificial MTM/PVA/NFX ternary composite films are aroused by the synergistic toughening from their building blocks.This synergistic fabrication protocol provides a facile approach to design and construct novel integrated nacre-like composite materials with potential applications in tissue engineering, and functional barrier coatings.4. Inspired by the aragonite microplatelets/chitin nanofibers-protein ternary layered structure of natural nacre, robust artificial Montmorillonite ?MTM?/starch/aragonite ternary composite films with nacre-like architecture are assembled based on the building blocks with different sizes and thickness by simple vacuum filtration technique. The lamellar architecture is alternately stacked by MTM nanosheet layer and aragonite platelets, and glued by starch. The typical nacre-like Montmorillonite/starch/aragonite ternary composite film shows a perfect combination of high strength ?228.1±14.8 MPa? and toughness (3.2 ± 0.2 MJ m^-3),higher than that of the binary MTM/starch composite film (148.4 ± 10.7 MPa,1.6 ± 0.1 MJ m^-3),and the binary aragonite/starch composite film (80.7 ± 8.1 MPa, 0.89 ± 0.05 MJ m^-3),and superior to nature nacre (80^-135 MPa, 1.8 MJ m^-3). The synergistic toughening effect is originating from high mechanical properties of aragonite platelets and lubrication of MTM nanosheets. This approach for constructing robust artificial nacre by synergistic effect from MTM nanosheets and aragonite platelets provides a creative opportunity for designing and fabricating integrated artificial nacre in the near future,and this kind of ternary artificial nacre has great potential applications in aerospace,tissue engineering, and biomedical fields.