A Molecular Dynamics Simulation Study Of The Thermal Properties Of Carbon Nanotubes/Graphene Filled Polymers

Experimental investigation on thermal conductive composites is expensive and time-consuming,while numerical simulation study could offer an alternative way to explore the thermal behavior of such composites with theoretical and practical value.In this thesis,we established a single-chain model of polydimethylsiloxane(PDMS),carbon nanotubes(CNT)/polydimethylsiloxane(PDMS),and graphene(GNP)/polydimethyl and studied the thermal conductivity of PDMS chain and CNT/PDMS composite structure and GNP/PDMS composite structure theoretically by using molecular dynamics method.The main research contents are as follows:A research path for molecular dynamics analysis was established,and data files for molecular dynamics calculations with the selected potential functions were obtained.According to the research goal,the script file of molecular dynamics calculation was prepared by selecting the appropriate thermal conductivity calculation method.Then,the molecular dynamics results were averaged to obtain the thermal conductivity of the simulated system.The PDMS chain model was built and the effects of time step,temperature,and chain length and chain number on the thermal conductivity of PDMS chain were studied.A time step of 0.25 femtoseconds(fs)was selected according to the calculation results.The trend of the thermal conductivity of the PDMS chain at temperature between 300K and 400K was obtained,as well as the correlation of thermal conductivity with chain length and number.A composite model of CNT/PDMS was father established and an aligned single-walled carbon nanotube/PDMS composite structure was proposed.We selected appropriate parameters to study the influence of the position,temperature and the number of PDMS chains insides the carbon nanotubes on the thermal conductivity of the composites model based on the results of PDMS chains.It was found that the thermal conductivity of the composite model decreases with increasing temperature when temperature between 120K and 210K,and the thermal conductivity shown different trends when different number of PDMS chains were placed inside the carbon nanotubes.A GNP/PDMS composite model was also established and an aligned graphene/PDMS composite structure was designed.After selecting the appropriate parameters,the thermal conductivity of GNP/PDMS composite model gradually decreased as the temperature increased from 120K to 210K.In addition,the thermal conductivity of the composite model was proportional to the number of PDMS chains.When the number is constant,the thermal conductivity of the composite model placed on one side was higher than that placed on both sides evenly.