Copyright 2018 ABSTRACT Interface Driven and Bio-mimetic Design of 3D Hybrid Materials by Peter SamoraOwuor The discovery of Graphene, carbon nanotubes and subsequent other nano-materials led to an explosion in research geared towards utilizing their intriguing mechanical, physical and chemical properties. While the physical properties of nanomaterials have been extensively explored, the assembly in a bottom-up approach to design hybrid 3D nanostructures by taking advantage of their interfacial properties still needs a deeper inquiry. This thesis scope is to answer four key questions; What role does the interfacial region plays in macro-scale materials properties? Is the same effect of interfacial region at macro-scale applies to the nano- scale materials? Is there a means to modify the interface region to assemble 3D hybrid structures? What are the resulting applications of such design in materials? To address the aforementioned questions, novel synthetic and biomimetic strategies were employed. The first detour of the thesis delves into the chemical process where functionalization and freeze-drying methods are used to fabricate porous carbon nanotubes (CNT) with self-stiffening behavior. The chemical approach is then applied to zero-dimensional SiO2 nanoparticles to fabricate three-dimensional nanostructures with improved fire-retardant capability. Next, the thesis explores the physical methods in assembling 3D structures where graphene oxide foam is chemically and physically reinforced with polymer molecule to fabricate an oil absorption and electrical resistant foam. The thesis further develops a new method to functionalize hexagonal boron nitride (h-BN) to enable their networking forming property resulting in high porous foam for CO2 absorption. The above solutions all relates to what is referred to as ‘hard interface’ therefore there was a need to explore ‘mobile interface’ like those found in nature. In this regard, a new area of study was developed; solid-liquid composite in macro-scale materials. Here, the thesis presents two new approaches; high damping composite by addition of liquid metal in a polymer matrix and optical and stiffness switching of a phase change composite. Finally, the thesis attempts to combine the two interfaces in hybrid materials. The most important contribution of this thesis is the new techniques which can be used to design advanced composites. Furthermore, a new subset of solid-liquid composites which have never been looked at in terms of mechanical properties is brought-forth. Finally, the peer-reviewed papers published should form a basis for future scientists with plans to pursue this field. Acknowledgments Since joining Rice University in the fall of 2014, I have received support and encouragement from many different people and here I would like to acknowledge those people. First, I would like to express gratitude to my major advisors: Professor Pulickel M. Ajayan and Professor Jun Lou for giving me the opportunity to work on this research project, their support and guidance and fruitful discussions. I wish to express my sincere thanks to Professor C. Fred Higgs III for accepting to be in my committee and his constructive discussion on my work. I would also like to thank Dr. Chandra Sekhar Tiwary for his advice and great help he offered to me; training on instruments, advice and lots of valuable literature among others. I would like to thank my colleagues at MSNE department for their help and friendship and for creating conducive atmosphere that broadened my understanding of other cultures. I would also like to thank MSNE staffs for their tireless help. Special thanks go to Mr. & Mrs. Curry for their ever ending support and lastly to my parents and whole family for their encouragement. Contents Acknowledgments ..................................................................................................... iv Contents .................................................................................................................... v List of Figures ............................................................................................................ ix Nomenclature ........................................................................................................ xviii I. Overview ............................................................................................................... 19 II. Introduction ......................................................................................................... 21 2.1. Role of Interfaces in Materials Design ................................................................... 21 2.2. Materials Design Approaches................................................................................. 24 2.2.1. Liquid exfoliation ............................................................................................. 24 2.2.2. Mechanical exfoliation .................................................................................... 26 2.2.3. Chemical vapor deposition .............................................................................. 27 2.2.4. Sol-gel method ................................................................................................. 28 2.3. Synthesis of Graphene Oxide ................................................................................. 30 III. Role of Interface Engineering in Assembling 3D Structures from Zero and One- dimensional Materials .............................................................................................. 32 3.1. Background ............................................................................................................. 33 3.1.1. Introduction ..................................................................................................... 33 3.2. Self-Stiffening Behavior of Reinforced Carbon Nanotubes Spheres ................. 33 3.2.1. Background ...................................................................................................... 34 3.2.2. Preparation of CNT Sphere and Composite..................................................... 35 3.2.3. Physical Characterization ................................................................................. 36 3.2.4. Simulation Details ............................................................................................ 36 3.2.5. Results and Discussion ..................................................................................... 37 3.3. Scalable Bottom-up Assembly of Ultra-Low Density Multifunctional Three- Dimensional Nanostructures from SiO2 ..................................................................... 45 3.3.1. Background ...................................................................................................... 45 3.3.2. Synthesis of SiO2 3D Nanostructures ............................................................... 46 3.3.3. Physical characterizations................................................................................ 47 vi 3.3.4. Simulation Details ............................................................................................ 48 3.3.5. Mechanical response of 3D SiO2 Structures .................................................... 49 3.4. Conclusion .............................................................................................................. 64 IV. Surface Modification of 2D Materials into 3D Hybrid Structures ........................... 65 4.1. Background ............................................................................................................. 66 4.2. High Toughness in Ultra low Density Graphene Oxide Foam ................................ 66 4.2.1. Background ...................................................................................................... 66 4.2.2. Preparation of interconnected Graphene Oxide Foam ................................... 68 4.2.3. Physical Characterization ................................................................................. 68 4.2.4. Simulation Details ............................................................................................ 70 4.2.5. Result and Discussion ...................................................................................... 71 4.3. Oxidation of hexagonal boron nitride (h-BN) nano-sheets to synthesize reactive sites for assembling of 3D structures ............................................................................ 82 4.3.1. Background ...................................................................................................... 82 4.3.2. Oxidation of h-BN ............................................................................................ 84 4.3.3. Preparation of oxidized h-BN/polyvinyl alcohol foam .................................... 84 4.3.4. Physical Characterization ................................................................................. 85 4.3.5. Simulation Details ............................................................................................ 86 4.3.6. Properties of Oxidized h-BN/PVA Foam .......................................................... 87 4.4. Conclusion ............................................................................................................ 103 V. Bio-mimicking of ‘Mobile’ Interfaces from Nature: Liquid Metal Composite ........ 104 5.1. Background ........................................................................................................... 105 5.1.1. Introduction ..................................................................................................