ADVANCED FABRICATION AND MULTIFUNCTIONAL PROPERTIES OF MORPHOLOGY-CONTROLLED GRAPHENE AEROGELS AND THEIR COMPOSITES FAN ZENG (B. Eng, Harbin Institute of Technology) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF MECHANICAL ENGINEEING NATIONAL UNIVERSITY OF SINGAPORE 2015 ACKNOWLEDGEMENTS I would like to convey my deepest and sincerest appreciation to my supervisors, Asst. Prof. Duong Hai Minh and Assoc. Prof. Christina Lim Y. H., for their invaluable guidance and constant support during my whole PhD candidature. The energy and enthusiasm that they have for research never fail to inspire me. I extend my sincere thanks to Assoc. Prof. Brian L. Wardle and all group members at Massachusetts Institute of Technology (MIT) for their warm hospitality and valuable suggestions for my research during my visit to NECSTlab. I am extremely grateful to my fellow group members, Dr. Nguyen Truong Son, Mr. Gong Feng, Ms. Feng Jingduo, Mr. Cheng Hanlin, Ms. Liu Peng, Mr. Tran Quyet Tran, Mr. Daniel Tng Z. Y., Ms. Clarisse Lim X. T., and Mr. Daryl Lim, for their devoted help and cooperation in my research work. I am also thankful to Asst. Prof. Chua Kian Jon, Dr. Zhao Xing, Mr. Sun Bo, and Asst. Prof. Amy Marconnet at Purdue University for their support regarding thermal conductivity measurements. I also thank the technical staff in Materials Laboratory, Mr. Thomas Tan, Mr. Ng Hongwei, Mr. Abdul Khalim Bin Abdul, and Mr. Juraimi B. Madon, and the technical staff in the Energy Conversion Laboratory, Mr. Tan Tiong Thiam, for their superior and professional technical support. i Finally, I gratefully acknowledge the Start-up Grant R-265-000-361-133, SERC 2011 Public Sector Research Funding (PSF) Grant R-265-000-424-305, and the China Scholarship Council (CSC) for providing financial support. ii TABLE OF CONTENTS ACKNOWLEDGEMENTS . i TABLE OF CONTENTS iii SUMMARY vii LIST OF TABLES ix LIST OF FIGURES . x CHAPTER 1: Introduction 1.1 Aerogels 1.1.1 Background 1.1.2 Carbon-based aerogels . 1.1.3 Drying techniques of aerogels . 1.1.4 General properties and applications of aerogels 1.2 Carbon-based nanocomposites 1.3 Objectives of thesis . 1.4 Organization of thesis . 11 CHAPTER 2: Literature Review 13 2.1 Graphene . 13 2.1.1 Introduction 13 2.1.2 Structure of graphene . 14 2.1.3 Synthesis methods of graphene 15 2.1.4 Properties of graphene . 24 2.1.5 Potential applications of graphene . 28 2.2 Graphene aerogels (GAs) 29 iii 2.2.1 Introduction 29 2.2.2 Graphene oxide (GO) . 31 2.2.3 Structure of GAs 34 2.2.4 Synthesis methods of GAs . 35 2.2.5 Properties of GAs . 39 2.2.6 Potential applications of GAs 42 2.3 Graphene–carbon nanotube (CNT) hybrid aerogels . 44 2.3.1 Introduction 44 2.3.2 Structure of graphene–CNT hybrid aerogels . 44 2.3.3 Synthesis methods of graphene–CNT hybrid aerogels 45 2.3.4 Properties and potential applications of graphene–CNT hybrid aerogels . 46 2.4 Graphene–polymer nanocomposites . 47 2.4.1 Introduction 47 2.4.2 Structure of graphene–polymer nanocomposites . 48 2.4.3 Synthesis methods of graphene–polymer nanocomposites 49 2.4.4 Properties of graphene–polymer nanocomposites . 50 2.4.5 Potential applications of graphene–polymer nanocomposites 54 CHAPTER 3: Experimental Section . 56 3.1 Materials . 56 3.2 Experimental techniques . 57 3.2.1 Synthesis of graphene oxide (GO) . 57 3.2.2 Synthesis of graphene aerogels (GAs) . 58 iv 3.2.3 Synthesis of graphene–CNT hybrid aerogels 59 3.2.4 Synthesis of GA–poly (methyl methacrylate) (PMMA) nanocomposites 59 3.3 Characterization 60 3.3.1 X-ray diffraction (XRD) 60 3.3.2 Scanning electron microscopy (SEM) . 60 3.3.3 Physical adsorption/desorption of nitrogen (BET) 61 3.3.4 Electrical conductivity measurement . 63 3.3.5 Thermal conductivity measurement . 64 3.3.6 Thermogravimetric analysis (TGA) . 67 3.3.7 Vickers microhardness measurement 67 CHAPTER 4: Morphology Control of Graphene Aerogels 69 4.1 Introduction . 69 4.2 Nanostructured control of graphene aerogels (GAs) 70 4.2.1 Effects of chemical compositions and synthesis conditions 72 4.2.2 Effects of reducing agents 76 4.2.3 Effects of CNTs . 77 4.3 Conclusions . 79 CHAPTER 5: Multifunctional Properties of Graphene Aerogels 80 5.1 Introduction . 80 5.2 Electrical property of graphene aerogels (GAs) . 81 5.2.1 Effects of chemical compositions and synthesis conditions 81 5.2.2 Effects of reducing agents 83 5.2.3 Effects of CNTs . 85 v 5.3 Thermal stability of graphene aerogels (GAs) 86 5.3.1 Effects of chemical compositions and synthesis conditions 86 5.3.2 Effects of reducing agent and CNTs 87 5.4 Thermal conductivity of graphene aerogels (GAs) . 88 5.4.1 Effects of chemical compositions 88 5.4.2 Effects of thermal annealing 93 5.4.3 Prediction of thermal boundary resistance and thermal conductivity of graphene nanosheets within GAs . 94 5.5 Conclusions . 96 CHAPTER 6: Advanced Multifunctional Graphene Aerogel–Poly (methyl methacrylate) Composites: Experiments and Modelling . 98 6.1 Introduction . 98 6.2 Structure of GA–PMMA nanocomposites 99 6.3 Electrical property of GA–PMMA nanocomposites . 101 6.4 Thermal stability of GA–PMMA nanocomposites . 103 6.5 Thermal property of GA–PMMA nanocomposites 104 6.6 Microhardness of GA–PMMA nanocomposites . 106 6.7 Conclusions . 109 CHAPTER 7: Conclusions and Recommendations . 111 7.1 Conclusions 111 7.2 Recommendations 114 REFERENCES . 116 LIST OF PUBLICATIONS 160 vi SUMMARY Graphene aerogels (GAs) having large surface area property of aerogels and excellent multifunctional properties of graphene nanosheets, can be promising candidates for energy storage devices and light-weight nanocomposites. For this research, a cost-effective method has been developed to synthesize self-assembled GAs from graphite at a low temperature range (45–95 oC) through modified Hummers’ and chemical reduction methods using various reducing agents (L-ascorbic acid, NaHSO3 and HI). The effects of synthesis conditions, reducing agents, thermal annealing processes and carbon nanotubes (CNTs) on the morphology, electrical and thermal properties of the as-prepared GAs are quantified comprehensively. The GA nanostructures are well controlled and have a large surface area of up to 577 m2/g. The CNT inclusions and annealing processes can enhance the electrical conductivity of the as-prepared GAs by up to five times, as measured via a two-probe method. For the first time, a comparative infrared microscopy technique has been successfully developed to measure the thermal conductivity of GAs, and the GAs having 0.67–2.50 vol. % graphene are measured to be 0.12–0.36 W/m·K accordingly. For light-weight but strong material development, GA–poly (methyl methacrylate) (PMMA) nanocomposites are further developed by backfilling PMMA into the pores of the GAs. Due to uniform distribution of the graphene nanosheets in the PMMA matrix, the GA–PMMA nanocomposites exhibit significant enhancements of electrical conductivity (0.16–0.86 S/m), vii microhardness (303.6–462.5 MPa), and thermal conductivity (0.35–0.70 W/m·K) over pure PMMA and the graphene–PMMA nanocomposites prepared by traditional powdery dispersion methods. The developed GAs and GA–PMMA nanocomposites in this thesis can be applied in aerospace, composite electrodes, biosensors, and energy harvest and storage devices. viii behavior and thermal, electrical, and electronic properties, Macromol. Chem. Phys., 2011, 212, 1951-1959. [226] J. Yu, P. Jiang, C. Wu, L. Wang, X. Wu, Graphene nanocomposites based on poly(vinylidene fluoride): Structure and properties, Polym. Compos., 2011, 32, 1483-1491. [227] T. 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Pandey, PMMA–CNT matrices for vacuum electronic, biosensing and energy applications, Department of Physics, Michigan Technological University, 2010. 159 LIST OF PUBLICATIONS 1. BOOK CHAPTER (1) Hai M. Duong, Zeng Fan, Son T. Nguyen, Carbon Nanotube/Graphene Aerogels, The Carbon Nanomaterials Sourcebook, Taylor & Francis (CRC Press), 2015. 2. JOURNAL PAPERS (1) Zeng Fan, Feng Gong, Son T. Nguyen, Hai M. Duong, Advanced multifunctional graphene aerogel–poly (methyl methacrylate) composites: Experiments and modeling, Carbon, 2015, 81, 396-404. (2) Zeng Fan, Amy Marconnet, Son T. Nguyen, Christina Y. H. Lim, Hai M. Duong, Effects of heat treatment on the thermal properties of highly nanoporous graphene aerogels using the infrared microscopy technique, International Journal of Heat and Mass Transfer, 2014, 76, 122-127. (3) Zeng Fan, Daniel Z. Y. Tng, Clarisse X. T. Lim, Peng Liu, Son T. Nguyen, Pengfei Xiao, Amy Marconnet, Christina Y. H. Lim, Hai M. Duong, Thermal and electrical properties of graphene/carbon nanotube aerogels, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2014, 445, 48-53. (4) Zeng Fan, Daniel Z. Y. Tng, Son T. Nguyen, Chunfu Lin, Pengfei Xiao, Li Lu, Hai M. Duong, Morphology effects on electrical and thermal properties of binderless graphene aerogels, Chemical Physics Letters, 2013, 561–562, 92-96. 160 (5) Son T. Nguyen, Hoa T. Nguyen, Ali Rinaldi, Nam P. V. Nguyen, Zeng Fan, Hai M. Duong, Morphology control and thermal stability of binderless-graphene aerogels from graphite for energy storage applications, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2012, 414, 352-358. (6) Jingduo Feng, Son T. Nguyen, Zeng Fan, Hai M. Duong, Advanced fabrication and oil absorption properties of superhydrophobic recycled cellulose aerogels, Chemical Engineering Journal, 2015, revised. 3. CONFERENCE PROCEEDINGS (1) Zeng Fan, Peng Liu, Thang Q. Tran, Hai M. Duong, Advanced fabrication of carbon nanotube aerogels by chemical vapor deposition. NT15, 29th June-3rd July 2015, Nagoya, Japan. (2) Thang Q. Tran, Peng Liu, Zeng Fan, Nigel H.H. Ngern, Hai M. Duong, Advanced multifunctional properties of aligned carbon nanotube–epoxy composites from carbon nanotube aerogel method, 2015 MRS Spring Meeting & Exhibit, 6th-10th April 2015, San Francisco, California, USA. (3) Peng Liu, Thang Q. Tran, Zeng Fan, Nigel H. H. Ngern, Hai M. Duong, Advanced multifunctional properties of aligned carbon nanotube–epoxy composites from carbon nanotube aerogel method, APS March Meeting 2015, 2nd-6th March 2015, San Antonio, Texas, USA. (4) Peng Liu, Zeng Fan, Abhik Damani, Thang Q. Tran, Hanlin Cheng, Son T. Nguyen, Vincent Tan, Hai M. Duong, Synthesis of carbon nanotube/graphene aerogel hybrid material by chemical vapor deposition 161 for energy storage devices, International Meeting on the Chemistry of Graphene and Carbon Nanotubes, 30th March-3rd April 2014, Riva del Garda, Italy. (5) Zeng Fan, Daniel Z. Y. Tng, Clarisse X. T. Lim, Son T. Nguyen, Amy Marconnet, Christina Y. H. Lim, Hai M. Duong, Electrical and thermal properties of morphology–controlled carbon nanotube/graphene aerogels, International Meeting on the Chemistry of Graphene and Carbon Nanotubes, 30th March-3rd April 2014, Riva del Garda, Italy. (6) Peng Liu, Zeng Fan, Thang Q. Tran, Hanlin Cheng, Son T. Nguyen, Hai M. Duong, Vertically aligned carbon nanotubes/graphene aerogels for energy storage devices, 22nd International Conference on Processing and Fabrication of Advanced Materials (PFAM XXII), 18th-20th December 2013, Kent Ridge Guild House, Singapore. (7) Hanlin Cheng, Stephanie C. P. Neo, Lilian Medina, Son T. Nguyen, Zeng Fan, Hai M. Duong, Carbon/MWNTs and PEDOT/MWNTs aerogel composites for supercapacitor application, International Conference on Materials for Advanced Technologies (ICMAT). 30th June-5th July 2013, Singapore. (8) Zeng Fan, Daniel Z. Y. Tng, Clarisse X. T. Lim, Chunfu Lin, Son T. Nguyen, Amy Marconnet, Hai M. Duong, Electrical and thermal properties of morphology–controlled graphene/carbon nanotube aerogels for energy storage devices, NT13 : Fourteen International Conference on the Science and Applications of Nanotubes, 24th-28th June 2013, Espoo, Finland. 162 (9) Zeng Fan, Daniel Z. Y. Tng, Son T. Nguyen, Jingduo Feng, Hai M. Duong. Morphology effects on electrical properties of advanced graphene aerogels, 2013 MRS Spring Meeting & Exhibit, 1st-5th April 2013, San Francisco, California, USA. (10) Shao Kai Ng, Jia Cheng Oh, Janet P. W. Wong, Son T. Nguyen, Zeng Fan, Hai M. Duong, Green recycled cellulose aerogels from waste paper for oil spill cleaning, 2013 MRS Spring Meeting & Exhibit, 1st-5th April 2013, San Francisco, California, USA. (11) Zeng Fan, Son T. Nguyen, Daniel Z. Y. Tng, Clarisse X. T. Lim, Jingduo Feng, Stephanie C. P. Neo, Hai M. Duong, Simple but effective method of morphology control of graphene aerogels for energy applications, Annual International Conference on Chemistry, Chemical Engineering and Chemical Process (CCECP 2013), 25th-26th February 2013, Singapore. 163 [...]... motivations of this thesis and provides some background on aerogels, in particular carbon-based aerogels Chapter 2 presents a specific literature review of the GAs and graphene- based nanocomposites, including their structure, synthesis methods, and multifunctional properties Chapter 3 provides a description of the materials, synthesis approach, and characterization of the developed GAs and GA–PMMA nanocomposites... types of aerogels, graphene aerogels, which are a novel type of carbon-based aerogels, are of particular interest for this study The utilization of graphene aerogels to prepare graphene aerogel-based nanocomposites could effectively solve the agglomeration problem of carbon fillers in carbon-filled nanocomposites, and further provides a promising application for graphene aerogels 1.1 Aerogels 1.1.1 Background... common type of carbon aerogels, CNT aerogels are developed based on the interesting properties of CNTs [21-23] They are essentially CNTs randomly accumulated in space and connected by some specific organic binder [11, 12] It has been indicated that CNT aerogels can offer high power density as the electrode materials of supercapacitors However, the high cost of CNT fabrication and difficulty of CNT dispersion... is often taken to mean the combination of a bulk matrix and one or more nanofillers (e.g nanoparticles, nanosheets, or nanofibers) Because of the high aspect ratio of the nanofillers, a nanocomposite can typically exhibit properties in one order greater than those conventional composites [40] To date, carbon-based nanofillers, especially CNTs and graphene, have been extensively investigated as the multifunctional. .. For the GAs consisting of graphene nanosheets in particular, this approach provides a novel route for property enhancements of the graphene- based polymer nanocomposites 1.3 Objectives of thesis This thesis aims to achieve an effective morphology control of the GAs synthesized by chemical reduction method, and investigate the effects of the GA morphology on their multifunctional properties In order to... control of the GAs 73 Table 4-2 Effects of reducing agent and addition of CNTs on morphology of the GAs 76 Table 5-1 Morphological effects on electrical property of the GAs 82 Table 5-2 Effects of reducing agent and addition of CNTs on electrical conductivity and thermal stability of the GAs 83 Table 5-3 Synthesis conditions, density, volume fraction and thermal conductivity of. .. includes separate sections on graphene, graphene aerogels (GAs) and the graphene polymer nanocomposites: each section includes subsections addressing the structures, synthesis methods, multifunctional properties and potential applications of the materials in question 2.1 Graphene 2.1.1 Introduction Graphene is a two-dimensional (2D) planar sheet which is composed of a monolayer of hexagonally packed carbon... nanocomposites and evaluate how it solves the agglomeration problem of graphene polymer nanocomposites prepared by the traditional powdery dispersion method This thesis work would provide a comprehensive and systematical study of synthesis parameters on the multifunctional properties of the GAs In particular, it would provide the first benchmark data of the thermal property of GAs The development of. .. equation, and a comparative study of microhardness between this work and previously reported graphene PMMA nanocomposites are also included For comparison purposes, the values of graphene loading reported in mass fraction (wt %) are converted to volume fraction (vol %) 108 xiii CHAPTER 1: Introduction This chapter provides a background of aerogels and nanocomposites Among the various types of aerogels, ... GAs and backfill polymer into the network of GAs to prepare GA–polymer nanocomposites by in situ polymerization; (b) Investigate the effects of synthesis conditions on the morphology and multifunctional properties of the GAs; (c) Develop an improved comparative infrared microscopy technique to characterize the thermal property of the GAs; (d) Develop and characterize the multifunctional property of . ADVANCED FABRICATION AND MULTIFUNCTIONAL PROPERTIES OF MORPHOLOGY- CONTROLLED GRAPHENE AEROGELS AND THEIR COMPOSITES FAN ZENG (B. Eng, Harbin Institute of Technology). of graphene polymer nanocomposites 48 2.4.3 Synthesis methods of graphene polymer nanocomposites 49 2.4.4 Properties of graphene polymer nanocomposites 50 2.4.5 Potential applications of graphene polymer. hybrid aerogels 44 2.3.3 Synthesis methods of graphene CNT hybrid aerogels 45 2.3.4 Properties and potential applications of graphene CNT hybrid aerogels 46 2.4 Graphene polymer nanocomposites