The Molecular Dynamics Study On The Structure And Properties Of The Carbon Nanotubes/Polyethylenes Composites

Since it was discovered in 1991,the Carbon nanotubes(CNTs)have attracted the much attention as nanoscaled materials. In fact, they have been applied widely in materials field because of their unique structural, mechanical, electronic, and luminescent properties. Moreover, the CNT/polymer composites have been an important research direction of the application of composites. In these composites, the CNT could not only improve the mechanic properties, but also prepare the function composite materials using their electronic properties and other properties.The studies of the CNT/polymer composites are difficult than that of the simple polymer matrix because of the complexity of the structure. Not only the polymer and the CNT should be investigated separately, but also the interface of them. The interface between polymer and CNT effects the structure and properties of the composite much.In fact, the CNTs could be considered as a bent surface, and the polymers are restrained on this surface. It could be come down to the adsorption and diffusion process of the polymer on the surface. The morphology could be investigated intuitionisticly through computer simulations. And they are also needed to investigate the formation mechanism of the CNT/polymer composites. Subsequently, the physical and chemical properties are suggested by the simulation results. The results could be helpful for the design of the CNT/polymer composites material.The various CNT/PE composites have been investigated by the classical molecular dynamics(MD) simulation at microcosmic level.(1)Classical MD simulations were carried out to investigate the absorption and diffusion process of the PE chains on the side-wall of the CNT(5,5) whose length was limited at different temperature systematically.First, the systems containing only one PE chain are investigated. Different degrees of polymerization from 50 to 80 at separate temperatures of 300K, 400K, 500K and 600K are considered to find out the best condition for pattern adsoption. The stability of the systems had been investigated by the diffusion coefficient of the PE chains and the interaction of the PE chain and CNT(5,5); the conformations and the distribution of the PE chains are characterized by the bond-orientation order parameter along z-direction, the mean radius of gyration Rg and The torsion angle distribution for the backbone of the PE chain. In particular, the PE chains keep approximately linear conformation, and extend along the axis of the CNT at the room temperature. It is also found that the most probable distance between the CNT and the C atoms in backbone of PE molecules only attribute to the temperature, and at T =300K, this distance is about 3.8?. Sequently, the systems containing more PE70 chains are investigated to pertain to the vapor deposition with dilute vapor density. Through the simulation, it is examined that the PE chains are absorbed on the surface of CNT and form stable composites with the nanotube as capsules.Our result may be helpful for finding a new pattern composite, moreover, an oriented electric or photoelectric behavior composite.(2)Classical MD simulations were carried out to investigate the absorption and diffusion process of the PE chains on the side-wall of the CNT(10,0) and CNT(9,0) whose length was unlimited at different temperature systematically. Also Different degrees of polymerization from 50 to 80 at separate temperatures of 300K and 600K are considered. As the CNT(9,0) is the semimetallic tube and the CNT(10,0) is the semiconducting tube, we focus on the effection of the helicity of the CNT to the structure and the properties of the composites.In the same way, the stability of the systems had been investigated by the diffusion coefficient of the PE chains and the interaction of the PE chain and CNTs; and the conformations and the distribution of the PE chains are characterized by the bond-orientation order parameter along z-direction and the torsion angle distribution for the backbone of the PE chain. It is found that the conformation of PE chains and the adsorption site depend on temperature and the radius of the CNTs mostly, had little relation to the style of the CNTs. The last, the most probable distance between the CNT and the C atoms in backbone of PE molecules are obtained from radial distribution function. The results show that the significance of the dimensional matching for the configuration of PE chains adsorbed on the sidewall of CNTs.(3)The adsorption of the polyethylene oligomers (PE) on the side-wall of the single wall carbon nanotubes (SWCNTs) which composed of SWCNT(5,5), SWCNT(10,0) and heterojunction was researched using by the classic molecular dynamic simulation. The PE chains could be adsorbed on the surface of SWCNTs we constructed easily and form composites with the SWCNTs. The results show that the configuration of the PE chains on the side-wall of the SWCNTs depends on the dimensional matching of PE and SWCNT. The patterned assembly was presented when the PE and SWCNTs matched in dimension. As the researches in this field almost focus on the electronic of the heterojunction, the study of the composites composed of CNT containing heterojunction and polymers by the computer simulations in atomic scale has actual meaning.Also, the interaction of the PE chain and CNTs was caculated to characterize the stability of the systems. The morphology of the PE chains adsorbed on the CNTs is investigated intuitionisticly. The conformations and the distribution of the PE chains are characterized by the bond-orientation order parameter along z-direction and the torsion angle distribution for the backbone of the PE chain.The results showed that the conformantions and the distribution of the PE chains on the side-wall CNTs containing the heterjunctions were depended on the lengths of CNTs which were divided by heterjunctions. The dimensional matching of lengths between PEs and CNTs was relatived with the conformations of the PE chains on the side-wall CNTs. When the lengths between PEs and CNTs,PEs on the side-wall CNTs could form the patterned assembly. Thus, the control of the patterned assembly can be obtained by heterjunctions in the CNTs.