Design Of Nanodevices For Fluid Based On Carbon Nanotubes

With the development of experimental technology, the synthesis of complex carbon nanotube related structures becomes true, which also brings some possibilities for us to study the properties and design nanodevices based on those structures in nanoscale. Using molecular dynamic simulation method, we have studied the structure and properties of those carbon nanotube intramolecular junctions and try to design some nanodevices on the basis of thos materials such as nanovalve, molecular sieve, nanocontainer for the storage of hydrogen and so on.1) The energy barrier of C60 moving in different types of carbon nanotube intramolecular junction was calculated. On the basis of those results, we have found some rules for the synthesis of carbon nanotube intramolecular junction and summarized that the difference of energy curves is resulted from the diameter difference of carbon nanotubes. In capped carbon nanotube, there will be two stable sites for C60 only if the diameter of tube is larger the tube (21,0). Besides, we got the similar result in the I type tube. For T type and crossed tubes, the smaller diameter difference of tubes forming the junction, the lower adsorption energy for C60 around the junction. Combining the above results, we can design several types of devices for fluid in nanoscale.2) There are two stable sites A and B for C60 in a one-way nanovalve based on a carbon nanotube intramolecular junction. Using molecular dynamics simulations, we demonstrate the flow behavior of helium through thenanovalve as controlled by the pressure balance around C60. The van der Waals interaction between C60 and carbon nanotube keeps C6 close to the junction, while the pressure balance around C60 can juggle it between two adsorption sites, which in turn closes or open the nanovalve.3) On the basis of a carbon nanotube intramolecular junction and a C60, a molecular sieve for H2 is proposed. The small interspace formed between C60 and the junction provides a size changeable nanochannel for the permselectivity of H2 while blocking Ne and Ar. The sieving mechanism is discussed in terms of soft repulsion of H2 and the size of the nanochannel. 4) A nanostructure, consisting of C60 enclosed within a carbon nanotube near its cone shaped cap, is shown to behave like a ball check valve, a pressure-driven device for the storage of fluid. The van der Waals force acts like a spring that traps C60 near the cap section with a potential well around 1 eV. The restricted interstitial space around the valve produces a volume difference that forces C60 near the top center of the cap and therefore blocks the outward diffusion. It is estimated that such a mechanism can produce nanocapsules with internal pressure up to 40 GPa.5) Functionalized carbon nanotube could scratch water molecules at low temperature working as a container for the storage of hydrogen which is called "aqueous valve". The amorphous ice structure aggregated around the carboxylic end of carbon nanotube and slow down the diffusion of hydrogen. By using molecular dynamic simulation, we calculated the diffusion barrier of hydrogen in valve (12,12)-COOH and(15,15)-COOH is around 0.85 eV and 0.67 eV respectively. The difference of storage ability is resulted from the compactness ice structure around the carboxylic groups.