Preparation And Properties Of Graphene Based Bioinspired Structural Materials

Materials with excellent mechanical strength and toughness are highly desirable in multiple applications including airplanes,national defense,and automotive industries.Currently,many natural materials are highly valued by most researchers,especially the nacre.After long-term evolution,their microstructure and corresponding macroscopic properties have basically tended to be optimized.Although the compositions of the nacre are simple,its unique"brick and mortar"assembly structure gives the shell excellent mechanical properties to adapt to environmental and functional needs.At present,inspired by natural materials,a series of assembly technologies have been developed to build lightweight bionic structural materials with high-strength and high-toughness,yet realizing industrial application by using these strategies remains a long-standing challenge limited by many factors like high equipment requirements,complex molding process,and difficulty in preparing large or complex three-dimensional products through assembling.In this paper,the bionic structural nanocomposites were designed through various strategies,and different interface interactions were introduced between the nanostructure units to realize the rapid assembly of bionic materials,providing new ideas for the efficient preparation of high-performance composites.The specific research contents are as follows:1.Magnetic graphene oxide（MGO）nanosheets were synthesized by decorating magnetic Fe₃O₄ nanoparticles on the surface of graphene oxide（GO）nanosheets and then assembled with poly（vinyl alcohol）（PVA）solution to form nacre-mimetic nanocomposites via the magnetic assembly technique.After that,the fracture behavior and energy dissipation process of MGO-PVA composite were studied and the results show that the tensile strength and toughness of the MGO-PVA film can reach 248.0±6.7 MPa and 7.0±0.5MJ/m³,which are 5.0 and 4.0 times higher than the pure MGO film,respectively.After in situ reduction by hydroiodic acid,the tensile strength reached as high as 340.0±6.2 MPa.2.A class of GO based artificial nacre material with self-healing capacity and recyclability due to non-covalent bonding interactions was fabricated by functionalization of graphene oxide with ellagic acid throughπ-πstacking followed by evaporation induced self assembling process between ellagic acid modified graphene oxide（EGO）and polyurethane（PU）.The artificial nacre displays a strict“brick-and-mortar”structure,with EGO nanosheets as the brick and PU as the mortar.The results showed that ellagic acid（ELA）was successfully adsorbed on GO surface,and when the mass ratio of PU to EGO was 3:1,the tensile strength and toughness of the material reached 111.2 MPa and 81.5 MJ m^-3,respectively（9.6 times and 1.8 times higher than that of PU）attributing to the interlayer slip of GO by breaking and recombing theπ-πbond dynamically through which the energy can dissipate when PU-EGO is subjected to tensile stress.In addition,owning to the existence of non-covalent bonds,the resulting polymer composites display good recyclability and even after repeated cyclic stretching/repeated processing,the strength of PU-EGO can still reach 95 MPa,and the elongation at break remains at its initial value.3.By blending the 3-mercaptopropyltrimethoxysilane（MPTS）modified graphene oxide（GO-SH）with thioctic acid（TA）,the thiol group of GO-SH can participate in the ring-opening polymerization（ROP）of dithiolanes thus the sulfur-containing polymer chains can be introduced into the surface of GO.With the addition of a small amount of water,the nanocomposites can be assembled into a pistachio-mimetic structure via repeated kneading and by removing the water,the ionic-bond cross-linked polymeric network can be reformed via the self-assembly of carboxylate groups.Research findings indicate that dried pistachio-mimetic nanocomposite（GO/p ST）exhibits excellent strength（260.8 MPa）and toughness(11.4 MJ m^-3)due to the“mortise and tenon”interlocking structure that can reduce the sensitivity of the layered structure to crack defects,the existence of polymer that can improve the interface effect and the ionic bond that can be used as a sacrificial bond prior to the main chain of the covalent bond to break.At the same time,the dynamic nature of the polymeric backbones endows the resultant GO-based composite with full recyclability and three-dimensional shapeability,and the resulted composites can maintain the shape with the removal of the water,overcoming the shortcomings of the traditional“brick and mortar”structural materials with complex molding and three-dimensional forming process.4.The natural wood was firstly processed via chemical treatment to obtain a delignified wood template with aligned mircochannels and then the wood mircochannels were coated with polydopamine（PDA）surface-modified small graphene oxide（PGO）nanosheets via assembly.With the existence of thin wood cell walls and large voids among the cellulose mircochannels,the highly aligned porous microstructure gives a way for polymers entry,resulting in the fabrication of the wood-polymer nanocomposite with inverse nacre structure（Different from the layered structural features of high inorganic content and low organic content in the nacre shells,the organic content in the layered-structural inverse nacre is as high as 90 wt%or more）.The tensile stiffness and strength of resulting nanocomposite reaches to 8.10 GPa and 90.3 MPa,with toughness upping to 5.0MJ m^-3.The thermal conductivity of nanocomposite is improved significantly by coating a PGO layer onto the wood scaffolds.The nanocomposite exhibits not only ultrahigh thermal conductivity(in-plane about 5.5 W m^-1K^-1 and through-plane about 2.1 W m^-1K^-1)but also satisfactory electrical insulation(volume resistivity of about 10¹⁵Ωcm).