Investigations Of Water And Ionic Crystal Filling Carbon Nanotubes: Dynamical, Electronic And Optical Properties

Nanomaterial and Nanodevice is one of the most important fields of nano science and technology in the 21th century, the development of which has got great promotion in recent years. Now, this cross-disciplinary field has been the most important frontier research subject receiving huge number of investment all over the world. Among nanomaterials, carbon nanotubes attract particular research attentions benefiting from its unique properties.Conceptually, carbon nanotubes can be formed by rolling up graphite sheets into tubular structures. This unique structure leads to high surface area with high adsorbability to gas, liquid and other molecules. Scientists found that carbon nanotubes can adsorb hydrogen and other gas molecules into their open cages by capillary filling. High capacity of gas adsorption will facilitate the applications of carbon nanotube acting as molecular storage and carriers of hydrogen fuel cell.Besides gases, other molecules and solutions, including DNA and protein, can be adsorbed into the cavity of carbon nanotubes. The most important agent in these processes is the most common solvent in nature, water. Water is widespread in natural environment, chemical reagents, and all living cells. It was proved that water molecules take an important role in maintaining the unblocked transport and the chemical potential balance near the cell membranes. Carbon nanotubes are very similar to these cross-membrane channels of living tissues, which can be used as the model for the study of biochemical interactions to reveal the unknown phenomena in nano-world and biosystems.The future of using carbon nanotubes as the molecules transport channels is very attractive. In nano-manipulate and nano-manufacture fields, carbon nanotubes can be built up into interlaced pipe networks. In the applications of nano-medicine, carbon nanotube probes can be used to transport nucleic acid, protein, and other chemical molecules, in order to deliver drugs into cells directly. Recently, Japanese scientistshad achieved this goal.However, the crucial problem in these applications is how to control the nanofluid inside carbon nanotubes. If we can not find an effective way to master the molecules in nanotubes, the success of molecules transportation devices will be impossible. Previous studies in the world did not deal well with it.Based on deepgoing analyses of molecular interactions, we proposed the "Controllable Transport Channel of Water NanofluicT concept, a way of controlling the transport of nanofluid through single-walled carbon nanotubes (SWNTs). By modifying the net charge of carbon nanotubes, we achieved the goal of controlling the transport properties of polar water molecules inside the carbon nanotubes. We also find the "Water Nanotubes" structures inside and outside carbon nanotubes, formed at room temperature. Recently, the model we proposed has been proved by experiments.Since carbon nanotubes can adsorb gas and liquid, the similar capillary filling of SWNTs should occur in the case of fused ionic crystals in liquid state. Then the recrystallization process of crystal molecules under special confinement from the carbon nanotubes during the cooling process will be a very important issue to investigate. For many reasons, experimental studies about these materials mainly focused on the crystals with heavy species. With the aid of supercomputers, we used ab initio quantum chemical method to calculate the interactions in the Carbon Nanotube-NaCl Crystal Complexes (CNNCC) for carbon nanotubes with various diameters and chiralities. Analyses of the dynamic interactions in the complex will provide essential information for experimentally exploring the potential applications of this material. Besides the dynamics simulations, we also computed the electronic properties and light absorption performance of the CNNCC.The following is the content list of key results of this dissertation.Chapter 4.In the works of this chapter, we study the interactions between various carbon nanotubes with different charges and water molecules, by combining the methods of Classical Molecular Dynamics Simulation and ab initio quantum chemical theory.We find that water molecules can be adsorbed into the cavity of opened carbon nanotubes, displaying polarized orientations. The 'Water Nanotubes" are formed inside and outside the carbon nanotubes with regular structures and regular density distributions.The electric field produced by the charged carbon nanotube makes the motion behavior of water molecules modulated, acting as the Transport Speed Regulator to control the penetration properties of water inside the carbon nanotube channels. These results are also very important for investigations of the liquid penetration and chemical potential balance of the pores or channels in biosystems and other related aqueous systems. The electron density distributions are also investigated by using ab initio quantum chemical method.Chapter 5.By investigating the interactions between single-walled carbon nanotubes charged with different charges and fused NaCl crystals, we find that the fused NaCl can fill up the cavity of carbon nanotubes. When the system is cooled down, the NaCl recrystallize into crystals and form the CNNCC. In this process, confinement from the carbon nanotube makes the NaCl crystal deformed remarkably, with the wall of the SWNT less deformed.However, NaCl inside the negatively charged carbon nanotubes can not form the normal simple cubic crystal structures. Instead, confined "Multi-walled NaCl Nanotubes" are formed. This structure is composed of alternated Na tubes and Cl tubes, which is totally different from the normal NaCl crystal structure.Chapter 6.Based on ab initio quantum chemical theory, we analyzed the dynamics properties and electronic structures of the CNNCC. It is found that the same NaCl crystal can be contained by carbon nanotubes with various diameters and types. Under the confinement from carbon nanotubes, NaCl crystals can represent stretchedor squashed type. In the deforming process, carbon nanotubes affect the Na+ ions greater than the Cl" ions. We point out that the simple van der Waals model cannot describe all the subtle forces in these systems. We also analyzed the key electronic properties of this complex by the computations of the band structure, the PDOS, and the density distributions of electrons.Chapter 7.In the works of this chapter, we used more accurate CI theory in conjunction with effective semi-empirical method to calculate the excited states and optical absorption properties of the CNNCC. Our results show that the confined NaCl ionic crystal can modulate substantially the optical absorption properties of carbon nanotube. Interactions between carbon nanotubes with different diameters and the confined NaCl crystals lead to different optical spectra. The results may promote researches on applications of the CNNCC structures on the field of the tunable infrared detector and the tunable polarizer device.