Experiment And Molecular Dynamics Simulation Of Organic Phase Change Materials Confined In Carbon Nanotubes

With the development of technology, the continuing miniaturization of microelectronic, optoelectronic, radiological devices and powerful computers is accompanied by further increases in their functionality, complexity and integration. The control and management of temperature plays a key role in maintaining the performance and precision of these devices. More than a half of Microelectronic device failure events are due to thermal reasons. The application of the novel composite confining phase change materials in carbon nanotubes is a prospective solution to mitigate the problem. In this paper, the structure and properties of organic phase change materials confined in carbon nanotubes were studied by experiments and simulations. In the experiments, the preparation and characterization of organic phase change materials confined in carbon nanotubes were performed. In the simulations, the distribution, phase transition and diffusion properties of paraffin molecules inside nanotubes were analyzed from the microscopic view. The experiment results were conformed with the simulation. Moreover, some researches were done to learn about the influence of diffusion property by the helicity of carbon nanotubes and the degree of filling. The main contents and conclusions are as follows:1. Paraffin waxes, Lauric acid and Stearic acid were successfully confined in carbon nanotubes materials, becoming a kind of composite with thermal storage ability. Their melting temperature decreased by 5.01, 3.61 and 2.85 oC respectively compared to pure phase change materials due to effect of the confined space in CNTs. The volume filling degree of carbon nanotubes filled with Paraffin waxes, Lauric acid and Stearic acid were calculated to be 26.27%, 10.02% and 31.90% respectively by analyzing the latent heat.2. A simple thermal interface device was designed to test the ability of the application in electronic thermal management of paraffin confined in carbon nanotubes. It was found that painting materials on the thermal interface can reduce the temperature difference between two sides. The temperature difference was 4.7 oC without painting thermal interface materials. When painting thermal grease, CNTs/thermal grease, acid treated CNTs/thermal grease and paraffin confined in CNTs/thermal grease on the interface, the temperature differences become 3.8, 3.1, 3.1 and 2.2 oC respectively. It indicated that the paraffin confined in CNTs material has a excellent heat transfer ability as the filler of thermal grease.3. The structure and diffusion properties of n-hexacosane with free state and nano-confined state were studied using Molecular Dynamics method. It reveals that the alkane molecules confined in CNT are almost spaced as ordered annular distribution, whose ordered degree are higher than the free state. The melting temperature of it is 4.1 oC lower than that of free state. The highly ordered structure and extreme confinement of CNT are the main factors for the decrease of melting temperature.4. The effect of CNTs helicity and filling degree on the system construction and diffusion property were analyzed. It indicates that the helicity of CNTs has little effect on the structure and degree of order. However, the constraint of armchair CNTs to the molecules is the strongest. The structure, degree of order and diffusion property are influenced by the filling degree. When the filling degree increases, the distribution of molecules becomes multilayer.