Investigation On Thermo-Mechanical Property Of Carbon-chain Polymers And Their Composites Via Molecular Dynamics Simulation

Polymers have been widely used in industrial production and daily life due to light weight,low cost,strong corrosion resistance,and easy of processing.However,the thermal transport property of traditional bulk polymers is poor due to various defects such as voids,impurities,and chaotic chain arrangement.In the field of heat dissipation for electronic devices,thermal interface materials with high thermal conductivity are often desired.In the chemical industry,corrosion-resistant plastic heat exchangers are necessary to use.In theoretical research,the abnormal thermal transport phenomenon like divergent thermal conductivity of polymer chain has been observed owing to the special structure.Therefore,studying the thermal transport mechanism in polymers and improving the thermomechanical properties of polymers have important theoretical value and practical significance.The thermal transport in different materials is firstly introduced from the perspective of carrier transport.Then the important concepts in molecular dynamics(MD)simulation and their applications in studying the thermo-mechanical properties of polymers and polymer composites are briefly reviewed.We use equilibrium molecular dynamics(EMD)simulation to calculate the thermal conductivity of woven polyethylene(PE),woven polyphenylene(PP),and woven polyacetylene(PA).We find that the thermal conductivity of woven polymers is intimately related to the stiffness of the polymer chain backbone.Furthermore,using carbon nanotube(CNT),boron nitride(BN)nanotube,and copper(Cu)nanowire as fillers,we calculate the thermal conductivity of PE-CNT,PE-BN,and PE-Cu via nonequilibrium molecular dynamics(NEMD)simulation.The results show that when the filler content is relatively low,the polymer matrix plays a dominant role in the thermal conductivity of the composite.The filler that can effectively improve the morphology of the polymer matrix should be selected.We further propose to use carbon nanotube junctions(CNTJ)as fillers to improve the thermal conductivity of polymers.The two-temperature model(TTM)is a phenomenological model that describes the coupled thermal transport of electrons and phonons.Using PE-Cu composite as a model,we combine TTM with NEMD simulation to investigate the impacts of the metal filler length and electron-phonon coupling strength on the thermal conductivity.With the help of the equivalent thermal circuit diagram,we find that the electronic non-local effects and EPN effects are equivalent to additional thermal resistances.Increasing the length of the metal filler can effectively reduce these two additional thermal resistances.When the length of the metal filler is fixed,increasing the electron-phonon coupling strength can reduce the EPN thermal resistance.A layer of BN nanotube is coated on the outside of the CNT to form a“core-shell” CNT-BN composite.We incorporate the coaxial CNT-BN filler into polyvinylidene fluoride(PVDF)and investigate the thermal transport property of the PVDF-BN-CNT composite under the electric field by MD simulation.We find that electric field can be used to effectively tailor the thermal conductivity of the PVDF composite.