Nanostructure Engineering and Mechanical/Electrochemical Performances of Nanocarbon Based Composite Films

Abstract

This study describes the preparation and characterization of novel carbon nanotube (CNT) based composite films with various tailored nanostructures for use in structural and multifunctional materials. CNTs have attracted great interest due to their unique mechanical, electrical, and thermal properties. This has stimulated fundamental research on the physical/chemical nature and versatile route for their technological applications in recent decades. However, macroscopic materials such as buckypaper, fiber, and yarn consisting of randomly oriented CNTs lose the intrinsic properties of individual CNTs against all expectations. In addition, previously reported CNT films with low interaction forces can degrade easily and lose performance by an external force. Methods to control the nanostructure have so far been unable to simultaneously satisfy performance, damage-tolerance, and high throughput. Therefore, a controlled assembly of CNTs in ordered nanostructures with strong interaction forces can lead to high strength CNT films. Chapter 1 provides a general introduction of the relevant physical/chemical parameters that contribute to strength and multifunctional capabilities of CNT based composite films. Additionally, the state-of-the art materials and unsolved issues are discussed. The aims of the present work are introduced considering the fundamental and theoretical issues. Chapter 2 presents a theoretical study for the strength of CNT film in comparison with the performance between previously reported experimental results. The correlation between the mechanical properties and the structural parameters is investigated to provide insight into the influencing factors. Theoretical modeling for the CNT film is conducted to indicate the performance of CNT films with the specified structure and interactions. Conclusively, the ideal structure and properties of CNT film based on the theoretical prediction are proposed. Chapters 3 and 4 discuss the preparation and properties of self-assembled, well-aligned CNTs and graphene oxide (GO)@CNT with a densely packed nanostructure as a strategy to develop unique load-bearing architecture for high strength film. Highly aligned CNTs with high packing density are prepared in the form of buckypaper via a simple filtration method. The CNT suspension concentration is strongly reflected in the alignment and assembly behavior of CNT buckypaper. We further demonstrated that the horizontally aligned CNT domain gradually increases in size when increasing the deposited CNT quantity. The resultant aligned buckypaper exhibited enhanced packing density, strength, modulus, and hardness compared to previously reported buckypapers. Furthermore, a novel approach in mimicking the natural bone structure is fabricating a hybrid composite paper based on GO and CNT. The size-tuning strategy enables smaller GO sheets to have more cross-linking reactions with CNTs and be homogeneously incorporated into CNT-assembled paper, which is advantageous for effective stress transfer. The resultant hybrid composite film has enhanced mechanical strength, modulus, toughness, and even electrical conductivity compared to previously reported CNT-GO based composites. We further demonstrate the usefulness of the size-tuned GOs as the stress transfer medium by performing in-situ Raman spectroscopy during the tensile test. Chapter 5 focuses on a design and characterization of tannic acid (TA)@CNT composite film that relies on bio-metal coordination bonds to strengthen the interaction forces between CNTs. The TA@CNT film exhibits very high strength and flexibility. The materials sustain their high energy storage performance upon extremely bended conditions and demonstrate their utilization for flexible energy storage systems.