The Study On Preparation And Properties Of Three Dimensional Graphene And Graphene-based Composites

Three-dimensional?3D?graphene is a new kind of carbon nanomaterials of graphene at macroscopic scale,which retains the intrinsic properties of graphene,such as high electrical conductivity,large specific area,superior mechanical properties and chemical stabiliy.The special porous microstructure of 3D graphene results in larger specific surface area,higher porosity,excellent compressibility,inter-connected conductive network and special microscopic surroundings,which indicates the possible application of 3D graphene in sensor,flexible electronics,thermal power engineering,loaded catalyst,and energy storage.However,the 3D graphene by typical methods are built by two-dimensional?2D?graphene at random,which causes poor control of structure and repeatability as well as imposes constrain to the excellent properties of graphene.3D printing is a new kind of additive manufacturing technology with advantages,including simplicity,speediness and ability to design.Unlike typical synthetic methods with assistance of template,3D printing can make the various 3D graphene with large size and controlled structure based on designable model,providing the technical support for the preparation of 3D graphene and its composite.In this thesis,3D printing are adopted for the controlled preparation of 3D graphene and tailorability of structure and property,in hope of providing reference for future work based on 3D graphene.At first,the graphene inks,including surfactant,thickening agent and low-boiling solvent,are prepared with different graphene contents.The rheological properties of inks show that apparent viscosity decreases from 10³ Pa?s to 0.1 Pa s at the range of shear rate 10^-110³ s^-1,indicating shear-thinning of inks required for 3D printing.The storage modulus of ink increases by an order of magnitude when the graphene content rises up from 25 wt%to 50 wt%,which strengthens the self-support of inks.The micromorphology of printed 3D graphene demonstrates alignment of graphene due to the uneven shear force when flowing through nozzle,leading to anisotropy that the transversal electrical conductivity is twice as higher as longitudinal electrical conductivity.The designable structure and properties are achieved by 3D printing with the adjustment of filament diameter,interlayer space and the like.At besides,3D graphene/SiC composites are obtained by introducing the SiC into3D graphene using chemical vapor infiltration?CVI?.Micromorphology of fracture surface suggests the uniform distribution of SiC and pull-out of graphene.Densification and morphology of 3D graphene/SiC are improved by increasing the gas pressure during CVI,enhancing compressive strength by two times.Prolonging the CVI time makes for the higher performance of composites.The compressive strength and electrical conductivity of sample after 50h CVI,180MPa and 2500 S/m,are superior to similar composites reported in previous literatures,demonstrating the advantages of 3D graphene/SiC by combining 3D printing and CVI.3D graphene/PDMS composites for strain sensor with high sensitivity and stretchability are also prepared by 3D printing.Printed 3D graphene/PDMS filament demonstrates high electrical conductivity 30 S/m and stretchable strain 170%,which can be used to detect the motion of joints and muscle in real time when attached to body parts,such as fingers,throat.The deformation is less 5%and maximal stress retention is nearly 100%after 90 compressive cycles,proving the excellent elasticity.Strain-electrical resistance curves demonstrate the great stability and real-time response under different compressive frequencies,strains and repeated compression.