Three-Dimensional Structural Construction Based On Carbon Nanotubes, Preparation And Performance Of Their Composites

Carbon nanotubes (CNTs), as important one-dimensional carbon materials, are composed of sp2/sp3-hybridized carbon atoms and possess fascinating electronic, mechanical, optical and thermal properties. Three-dimensional (3D) CNTs hybrid structures possess interconnected pores, high porosity, large specific surface area and exceptional transport channel of phonon/charge carriers, and are widely applied in the fields of microelectronics, energy storage, heat transfer, and sensor. Despite numerous advances in preparation and properties of 3D CNTs hybrid structures, the preparation processes, such as magnetron sputter deposition, chemical vapor deposition, and sol-gel method, are pretty complexed and expensive. Herein, it is highly desirable to develop simple and effective methods to assemble CNTs to form 3D porous hybrid architectures with controlled structure and morphology, and to investigate their assembly mechanism and properties, which plays an important role in enriching the applications of CNTs. In the work, CNTs as basic building blocks, are assembled into 3D hybrid architectures with controlled structure via different assembling approaches, and their corresponding assembling mechanism, properties and applications are also investigated. The main work is summarized as follows:1. Preparation and properties investigation of 3D N-doped CNTs (N-CNTs) sponges. N-CNTs are oxided in the mixture of H2SO4/HNO3 to be water-soluble, then 3D N-CNTs sponges are fabricated via ice template. The route is simple and feasible to control the structure in sponges via tuning the freezing temperature. The as-prepared sponges possess low density and high flexibility, and also exhibit nonlinear current-voltage (Ⅰ-Ⅴ) characteristics. Moreover, the sponges possess various electric resistance under different strains, which could be employed as strain-gauge sensors.2. Preparation and properties investigation of covalently bonded 3D N-CNTs/Ag hybrid sponges. To enhance the mechanical stability and strain-sensitivity of N-CNTs based sponges, we develop a versatile method of introducing covalent linkage between individual N-CNTs utilizing hyperbranched polyglycerol (HPG) as bridges and decorating the N-CNTs with Ag nanoparticles (NPs) using HPG as templates simultaneously, which gives rise to covalently bonded N-CNTs/Ag hybrids. The resultant hybrids are assembled into covalently bonded sponges by ice template, and the pore size of the sponges could be controlled via freezing temperature. The covalent bonding endows the sponges with structural stability under compression, oscillation, and bending modes; and the Ag NPs on the compartmental films can be considered as interlocked nanodomes to generate huge variation of contact area under mechanical deformation. These novel designs featuring interlocked geometry and covalent bonding allow the hybrid sponges to possess excellent stability and sensitivity as strain-gauge sensors.3. Preparation and properties investigation of pyramidal N-CNTs/Ag sponges. To further enhance the strain-sensitivity of N-CNTs/Ag sponges, pyramidal N-CNTs/Ag hybrid sponges are fabricated via ice template. The key novelty is to tune hierarchical structure, which includes nanostructure (design of N-CNTs/Ag hybrids), microstructure (design of porous sponges) and macrostructure (design of pyramidal shape). According to percolation theory, the resistance mutation of sponges could be achieved via tuning the ratio between the conductive fillers and alginate, and the gauge factor (GF) is 15 under strain of 3%. The high sensitivity mainly originates from the contact resistance between the interfaces of conductive sponge and copper electrode, which is confirmed by top electrode design and structure design of sponges/polydimethylsiloxane (PDMS), respectively. Encapsulated sponges not only possess robust mechanical stability, but also have low energy dissipation and plastic deformation under compression.4. Preparation and properties investigation of multifunctional porous N-CNTs hybrid architectures (CHAs). To enrich the multifunctionality of CHAs, layer-by-layer (LbL) assembly is employed to incorporate various functional nanomaterials with N-CNTs into such 3D porous CHAs. The key novelty to assemble such binary CHAs lies in synthesis of hyperbranched polyamidoamine as surfactant and cationic layer for immobilizing various nanostructured materials, selection of alginate bonding oxided N-CNTs as anionic layer, and selection of polyurethane (PU) sponges as skeletons tranferring load from CHAs to PU skeletons under deformation. The properties of CHAs could be tuned via controlling the number of deposited layer. The as-prepared CHAs possess high flexibility, strong adhesion to functional nanoparticles, and excellent resistance-strain stability, so that they could be employed as flexible conductors, strain-gauge sensors and heterogeneous catalysts, respctively.5. Preparation and properties investigation of multifunctional folded structured single-walled CNTs (SCNTs) hybrid paper. Sponges could be transformed into paper-like architectures when enough load is applied to prevent the recovery of skeletons in sponges. Inspired by the structure changes, multifunctional folded SCNTs-based papers are developed via a series of processes including homogenizing-freeze drying-compress ion technique. The folded porous structure enables the SCNTs hybrid papers to possess excellent electric resistance-strain stability during tension and compression bending process. Meanwhile, the compartmental structure absorbs paraffin to obtain phase-change composites, on which the contact angle of water could be controlled.