Zhejiang University’s Gaochao and Xu Zhen team "AFM": The intercalation plasticizing spinning method is used in the preparation of high crystallinity graphene fibers.

Graphene fiber is a continuous phase assembly material composed of graphene sheets stacked in an orderly manner along the axial direction.
It was first proposed and prepared by the team of Professor Gao Chao from the Department of Polymer Science of Zhejiang University in 2011 and was the first to prepare a new high-performance, multi-functional carbon-based fiber.
With the characteristics of high electrical conductivity, high thermal conductivity, low density, etc.
, it has shown attractive prospects in flexible wires, supercapacitors, solar cells, lithium batteries, sensors, etc.
, and has become a new academic research hotspot
.
Different from the previous carbon fiber, the building element of graphene fiber is a two-dimensional crystalline graphene with good electrical conductivity, thermal conductivity, mechanical strength, etc.
The internal structure of the fiber is three-dimensionally ordered, dense and uniform, and has the potential to convert carbon The performance of the fiber is pushed to a new stage
.
The main raw material for the preparation of graphene fibers is graphene oxide, and its assembly methods are diverse.
The current mainstream technical method is liquid crystal wet spinning
.
In the wet spinning process, the graphene oxide liquid crystal undergoes some processes such as shear flow, solidification forming, and drawing orientation to obtain densely structured graphene oxide fibers, and then after reduction and graphitization treatments, graphene can be obtained Fiber
.
The microstructure of the macroscopic graphene fiber assembly strongly depends on the conformation of the graphene sheet.
In particular, the random wrinkle conformation of graphene inevitably leads to loose stacking and irregular arrangement, resulting in low crystallinity of graphene fibers
.
Therefore, how to finely control the conformation of graphene sheets to eliminate random wrinkles is an important challenge to further advance the comprehensive performance of graphene fibers
.
[Work Highlights] "In response to this problem, the team of Professor Gaochao and Xu Zhen of Zhejiang University and the team of Professor Ma Weigang of Tsinghua University have recently carried out systematic and in-depth research based on the structure regulation of graphene fibers and the relationship between structure and performance
.
The "solvent intercalation plasticizing and stretching crystallization" method has developed a cascade plasticizing spinning technology, which effectively eliminates the wrinkles of the graphene sheets, promotes the effective arrangement of the approximate crystals of the graphene sheets, and further advances The comprehensive performance of graphene fiber
.
The fiber has high mechanical strength (3.
4? GPa), electrical conductivity (1.
19×106?? S/m) and thermal conductivity (1480 W/mK), and initially has the integration of structure and function.
Performance advantages, showing great prospects for industrial applications
.
Related work was published in Advanced Functional Materials with the title "Highly Crystalline Graphene Fibers with Superior Strength and Conductivities by Plasticization Spinning"
.
Figure 1 Plasticizing spinning method to prepare highly crystalline graphene fibers, and plasticizer stretching induces crystallization of graphene fibers? [Graphic analysis] Thermoplasticization is an important feature of preparing high-performance polymer fibers.
Inspired by this, this article Various plasticizers are intercalated between GO sheets to cause elastoplastic transformation and significantly increase the shape
.
The tensile strain of the graphene fiber before plasticization is only 5% (2% in the elastic region and 3% in the plastic region); after inserting a plasticizer (such as 80% acetic acid), the tensile strain reaches 34%, and the elastic region is almost not Change, and the plastic zone reaches 32%
.
XRD analysis showed that the interlayer spacing increased significantly, and the correlation between interlayer spacing and tensile strain was obtained.
Through structural analysis, the interlayer-controlled graphene interlayer spacing induction was obtained from the perspective of graphene interlayer spacing and wrinkle conformation.
The plastic transformation of graphene fibers
.
In the plastic state, the sliding of adjacent GO sheets is activated and rearranged into a flat conformation under tension, which can be proved by optical microscopy and small-angle X-ray scattering
.
Figure 2 Graphene fiber stress-strain curve, XRD interlayer spacing of different plasticizers, van der Waals effect, interlayer spacing and strain relationship curve, small-angle scattering and GO sliding and fold flattening schematic diagram.
Through the above mechanism analysis, the team established A cascade plasticizing spinning process for preparing graphene fibers with high crystallinity is developed, and the cascade stretching maintains the continuity of fiber spinning
.
It can be observed by SEM that the diameter of the graphene fiber is reduced from 14 μm to 6 μm, and the radial wrinkles on the surface gradually disappear along the fiber direction; the orientation degree of the graphene 002 plane is significantly improved by wide-angle X-ray scattering calculation
.
? Figure 3 Continuous cascade plasticizing spinning process, graphene fiber SEM, WAXS analysis and its orientation and density? GO fiber is further graphitized, and the azimuth scan and radial scan integral plots show that: with the increase of SR , The orientation degree of graphene fibers has been improved, indicating that the structure is more closely arranged; in WAXS, the half-value widths of the 100 and 002 peaks obtained by radial scanning in the qy and qx directions represent the lateral length and thickness of the graphite crystallites.
The crystal length of the graphene fiber with a SR of 32% is increased to 174.
3 nm, which is 220% more than that of the unplasticized graphene fiber; compared with the graphene fiber prepared before, the crystal size of the graphene fiber prepared by plasticized spinning is increased.
Due to the dense and neatly arranged microstructure induced by plasticized spinning, the same result was observed by high-resolution transmission electron microscopy
.
Figure 4 Crystal structure and electron microscope image of graphene fiber.
Plasticized spun graphene fiber has a multi-scale crystalline ordered structure and larger crystal size, which gives it excellent Young's modulus and tensile strength, and it varies with SR Increase and increase significantly: When SR is 32%, its tensile strength and Young's modulus are 3.
4 GPa and 341.
7 GPa, respectively, which are 200% stronger than unplasticized graphene fibers and 54% higher than previously reported graphene fibers.
%
.
The improvement in performance is mainly due to its dense and regular arrangement of graphene sheet structure, which reduces grain boundary defects and stress localization.
It is different from the size mixing strategy reported by Professor Lian Jie to prepare graphene fibers.
This time, it uses The plasticized spinning method prepares graphene fibers with a higher density, making full use of the advantages of large-size graphene units.
The close-packed structure and large sheet size enable graphene fibers to obtain higher electrical and thermal conductivity.
As the grain size increases, the thermal conductivity and electrical conductivity increase more obviously
.
Figure 5? Graphene fiber tensile properties, electrical conductivity and thermal conductivity? [Summary] This article developed a new type of cascade plasticized spinning to prepare graphene fibers with high mechanical properties, high crystallinity and high electrical thermal conductivity.
Method, this method innovatively transforms the random wrinkled conformation of graphene sheets into a flat structure, which is conducive to its close packing and orderly arrangement.
This strategy is a macroscopic carbon fiber towards a structure with high mechanical properties and strong functional characteristics.
Functional integration of single crystal graphite whiskers has opened the way
.