Study On The Effect Of Cross-linked Molecular Structure On The Properties Of Macroscopic Graphene Fibers

Graphene is a planar thin-layer material composed of sp²-hybridized C atoms with unique atomic thickness and strict honeycomb lattice network,which endow graphene with various excellent physical and chemical properties.It is of great theoretical and practical significance to fully transfer the excellent properties at the molecular level of graphene into macroscopic materials.Therefore,macroscopic graphene fibers（GF）composed of graphene sheets stacked and assembled in a one-dimensional confined space have caused a new research upsurge,showing great application prospects in healthcare,flexible devices,energy storage,conversion and other fields.Graphene oxide（GO）has abundant surface oxygen-containing groups and is highly dispersible in various common solvents including water,it facilitates the assembly of GO into macroscopic fibers via interfacial interactions and the conversion to GF via chemical/thermal reduction.Although the current technology for preparing GO macrofibers by wet spinning has become increasingly mature.However,the interfacial interaction between graphene units in the assembly and its influence mechanism on fiber properties are still unclear,which limits the improvement of the overall performance of macroscopic fibers to a certain extent.Accordingly,this dissertation the interfacial interaction with GO was regulated by selecting molecules with different structures as cross-linking agents,and the effect of cross-linking molecular structure on fiber properties was studied.The main contents are as follows:1.GO sheets with larger lateral dimensions were synthesized.The natural expanded graphite was oxidized by Hummers method and the shear exfoliation process was optimized to obtain GO with abundant oxygen-containing functional groups on the surface.Its monolayer nature was confirmed by atomic force microscopy（AFM）,and the lateral dimensions were mainly distributed in the range of 30-60μm.This large aspect ratio enables GO to form a long-range ordered liquid crystal phase even at concentrations as low as 0.5 mg m L^-1.2.The interfacial interaction mechanism of GO was determined when aliphatic amines were used as cross-linking molecules.Fibers were prepared using large-sized GO as the precursor and aliphatic diamines as the cross-linking molecules.The ionic interaction between amino group and GO was confirmed by infrared spectroscopy（IR）,X-ray photoelectron spectroscopy（XPS）and other characterization methods.By changing the chain length of aliphatic diamines,the fiber properties were regulated,and it was found that molecules with shorter chain lengths resulted in denser,more ordered,and stronger GO stacking.Thus,the obtained optimal fibers have a strength of 1.2GPa and a conductivity of 1.69×10⁴ S m^-1.3.The influence of the structure of aromatic amines on the properties of fibers was revealed when they were used as cross-linking molecules.Using aromatic diamines with different structures as cross-linking agents,the fibers were cross-linked by covalent andπ-πstacking,and GFs with optimized properties were obtained.The tightly packed and ordered structure of graphene sheets in fibers was characterized by means of X-ray diffraction（XRD）and scanning electron microscopy（SEM）.After tensile and electrical tests,it is found that the strength of the fiber with the highest mechanical properties can reach 2.1 GPa,while the electrical conductivity of the fiber with the best electrical conductivity can reach 4.96×10⁴ S m^-1,both of which are better than the reported GF under the same conditions.To sum up,this thesis aims to improve the overall performance of the fiber.By selecting cross-linked molecules with different structures to modulate the interfacial interaction and microstructure of GO,a performance-optimized GF is obtained.This not only confirms the correlation between macroscopic fiber properties and cross-linked molecular structure,but also provides a way to explore the preparation of high-performance GFs.