Wet spinning of 2D nanomaterial fiber

다국어 초록 (Multilingual Abstract)

The 2D crystal structures have a unique combination of mechanical properties, with high in-plane stiffness and strength but extremely low flexural rigidity. The family of 2D materials offers a full spectrum of physical properties, from conducting graphene to semiconducting MoS2 and to insulating h-BN. However, in the micro-scale, their properties are significantly inferior to the intrinsic materials, partly due to the Griffith criterion, but also the presence of mechanically inferior agglomerates, poor alignment versus the shear direction, and presence of voids. In other words, the performance of the graphene material is determined by the quality of assembly.
Fiber is a representative example of the anisotropic assembly. Graphene sheets form a lamellar structure, and thus strong attraction between sheets is expected. In addition, micro-scale deformation through shear stress is possible during fiber processing, and it is easy to control the internal structure of fibers more delicately. Since the lyotropic liquid crystal property of GO dispersion, deformation by shear stress is easily achieved.
In order to fabricate strong graphene fibers, it is important to understand the parameters that inhibit the properties of graphene fibers. These parameters is found in previous researchs about polymer fiber. The parameters that determine the properties of the polymer fibers were 1) entanglement between the polymer chains, 2) degree of orientation of the structure, 3) micro voids in fiber, and 4) defects at the polymer chain end. In graphene fibers, the parameters is presented similarly. The properties of graphene fibers are determined by 1) attraction between graphene sheets, 2) orientation of graphene sheets, 3) micro-pore between graphene stacked layers, and 4) sheet boundary at the edge of graphene. However, graphene assembled fibers have weak interaction between sheets. Also, since the weak interaction between sheets, it is difficult to align the graphene sheets using shear stress. In addition, the properties of graphene fiber were degraded by voids and sheet boundaries generated during the reduction process of GO.
According to the previous works, there are 3 remained challenges. 1)Control of orientation during wet spinning process. 2) Reinforcement of sheet attraction and minimization of structural defects without ultra-high temperature treatment. 3) Control of gas generation causing micro-pore. Corresponding to the problems, 3 strategies were studied to solve the challenges. 1) Orientation by drawing process via rheological modeling study 2) CNT reinforced graphene hybrid fiber. 3) Polyacrylonitrile/graphene carbon fiber for ultra-strong mechanical properties.
Herein, by utilizing the hybrid and coagulation-stretching processes, ultra-strong and electro-conductive graphene fibers was achieved with improved results which is higher than the previous reports without the high temperature treatment. The torsional properties of graphene fibers were reported for the first time, and the shear strength and modulus of graphene fibers were superior to conventional metals and polymers, and the density was much lighter than metals. In addition, by applying graphene wet-spinning method, the highly electro-conductive MXene fiber was demonstrated. Since most of the dispersion of 2D nanomaterials uses the mechanism of electrostatic charged surfaces like GO, it is considered that graphene oxide spinning studies would be applied universally to 2D nanomaterials systems.

목차 (Table of Contents)

• Introduction 1
• 1. Background of two-dimensional nanomaterials 1
• 2. Assembly of 2D nanomaterials 5
• 3. Wet spinning of 2D nanomaterials 5
• 4. Parameters for 2D fiber with high performances 8
• 5. Research scope and objectives 11
• Experimental 13
• 1. Materials 13
• 2. Synthesis and characterization of Graphene oxide, carbon nanotubes and MXene 14
• 3. Rheological characterization of GO, CNT/GO, Polyacrylonitrile/GO and MXene dispersion 20
• 4. Wet spinning of GO, CNT/GO, PAN/GO and MXene fiber 21
• 5. Reduction of CNT/GO and PAN/GO fiber 24
• 6. Characterization of the fibers properties 28
• Results and Discussion 40
• Part 1. Rheological modeling for wet spinning 40
• 1.1. Selection of rheological model system and equation 40
• 1.2. Calculation of stress induced by ejection rate and take-up rate using Navier-Strokes equation 45
• 1.3. Calculation of mean shear stress from take-up rate 49
• 1.4. Calculation of the yield stress using the Derjaguin-Landau-Verwey-Overbeek interaction model 49
• 1.5. Calculation of yield stress using Casson's equation 50
• 1.6. Drawing of GO fiber with rheological model system 53
• 1.7. Effect of drawing on graphene fiber 56
• Part 2. Highly oriented CNT/Graphene hybrid fiber 58
• 2.1. Effects of CNT intercalation on graphene fiber 58
• 2.2. Rheological properties of CNT/GO dispersion 59
• 2.3. Structural investigation of drawn CNT/Graphene fiber 70
• 2.4. Mechanical and electrical properties of D-HF 73
• 2.5. Torsional properties of D-HF 75
• 2.6. Torsional-electrical energy generator using D-HF 81
• 2.7. Comparison with the traditional materials 89
• Part 3. Ultra-strong PAN/GO derived Graphene fiber 95
• 3.1. Effect of PAN on graphene fiber 95
• 3.2. Rheological properties of PAN/GO dispersion 97
• 3.3. Reaction mechanism of PAN/GO fiber during thermal reduction 99
• 3.4. Effect of tension force during thermal reduction of PAN/GO fiber 101
• 3.5. Structural investigation of carbonized PAN/Graphene fiber 103
• 3.6. Mechanical and electrical properties of P/GF 105
• 3.7. Comparison with the traditional materials 108
• Part 4. Wet spinning of MXene assembled fiber for high electrical conductivity 111
• 4.1. Superiority of MXene and its Fiberization 111
• 4.2. Structural and chemical investigation of MXene 115
• 4.3. Rheological properties of MXene dispersion 122
• 4.4. Wet spinning of MXene fiber (MF) 127
• 4.5. Mechanical and electrical properties of MF 130
• 4.6. Application of MF 132
• 4.7. Comparison with the previous Graphene and MXene based fiber 134
• Conclusions 137
• References 139
• 국 문 초 록 154
• Appendix 158