Molecular Dynamics Research On Normal Thermal Conductivity Of SWCNT/NR Composite

With the rapid expansion of science and technology, the requirement for new materials become very urgent. This includes the need for a new thermally conductive material. Thermal conductive material appears in all fields of the national economy and defense technology. It is hoped that the new thermal material is not only to have anti-wear, compression and other excellent properties, but also have a high thermal conductivity.Carbon nanotubes are an excellent thermal conductivity material, and therefore been recognized as an ideal thermal conductive agent to improve the thermal conductivity of polymer composite materials. Object of this study is the carbon nanotubes/natural rubber composite, equilibrium molecular dynamics method (MD) was used. Effect of both molecular dynamics time steps and crosslink density on the thermal conductivity of natural rubber has been calculated by simulation. Chemi-adsorbed carbon nanotubes at random positions through covalent bonding (chemisorption) has been calculated as a function of adsorption density using molecular dynamics. Finally, relevant researches are done on the thermal conductivity of nanotube/natural rubber.Firstly, effect of different time steps on the thermal conductivity of natural rubber was simulated. Heat current autocorrelation functions of natural rubber are calculated for a long time, and then converged thermal conductivity results are obtained and compared. The results show that when the timestep is below 0.1fs, thermal conductivity is stable at around 0.35 W·m-1·K-1, which is similar to the practical results. If the selected time step is greater than 0.1fs, the larger the time step is, the higher the thermal conductivity will be. Thus the result loses its accuracy. The impact of crosslink density on the thermal conductivity of isoprene chains is studied. Here, the effect of cross-linking on the thermal conductivity was simulated using the form of covalent linkage. The calculation results show that unconnected individual isoprene chains have a relatively high thermal conductivity along the molecular chain axis direction. However, covalent linked chains get significantly lower thermal conductivities. Additionally, the higher crosslink density it exists, the lower thermal conductivities it will get. From the research of thermal conductivity of carbon nanotubes with chemisorption, it was found that the pristine carbon nanotube exhibits a high thermal conductivity due to its good structure, and the modified one shows a rapid drop in thermal conductivity even the chemisorption is as little as 0.5%. Additionally, reductions of thermal conductivity caused by different functional groups are in the same level. Study of the thermal conductivity of carbon nanotubes/natural rubber composite shows that the carbon nanotubes filled in nature rubber will improve the thermal properties of the composites obviously; and when the carbon nanotubes were connected with natural rubber by covalent bond, the thermal conductivity between filler and matrix can be improved, so that the thermal conductivity of the composite is further increased.