Computer Simulation Study On Thermal Conductivity Of Rubber Matrix Composites

At present,with the increasingly rapid development of modern electronic products,especially with the emergence of increasingly miniaturized,dense and large energy-consuming microelectronic devices,it has become increasingly important to solve the problem of heat transfer between devices.Thermal conductive silicone rubber(SiR)is a typical thermal interface material,which plays a key role in sealing,damping and heat dissipation.Polydimethylsiloxane(PDMS)is one of the most common silicone rubbers in industrial use.This polymer has been widely used in many equipment requiring heat dissipation.However,rubber material has a poor thermal conductivity.At present,the thermal conductivity of rubber material is improved mainly by filling thermal conductivity filler.But when the fraction of thermal conductivity filler is relatively large,the filler is easy to reunite,so that the improvement of thermal conductivity is limited.Based on previous studies,we investigated the effects of MoS2 and hybrid h-BN/MoS2 fillers on the thermal conductivity of PDMS composites using RNEMD simulation with an all-atomistic model.The work of this paper is carried out from three main aspects:1.Thermal conductivity of MoS2 and BNFor two-dimensional nanomaterials,the length of the material has a great impact on its own thermal conductivity,so understanding the relationship between the thermal conductivity and length of two-dimensional nanomaterials is of great significance for its practical application.Here,we use full atomic molecular dynamics simulation.Firstly,we use Material Studio to construct a series of monolayer MoS2 and BN nanoribbons with the size of 1-50nm to study the thermal conductivity of the two kinds of filler.The thermal conductivity of MoS2 and BN nanoribbons is very sensitive to their length,and increases with the length.The thermal conductivity of BN is about one order of magnitude larger than that of Mo S2 for the same dimensions.In addition to this,the number of layers does not have the same nor the same effect on the thermal conductivity of the two materials.2.Thermal conductivity of PDMS/Mo S2 compositesIn this part,we added a monolayer MoS2 to the PDMS matrix chain to discuss the influence of Mo S2 on the thermal conductivity of PDMS composites.The results are as follows:(1)after adding MoS2 to the PDMS matrix,the overall thermal conductivity of PDMS/MoS2 composite materials increases firstly and then decreases with the increase of MoS2 filling fraction;(2)Due to the poor affinity between MoS2 and PDMS,the addition of a large number of fillers causes the PDMS matrix chain to become curled,so there are holes in the materials.This is the main reason why the thermal conductivity of PDMS/MoS2 composites decreases when the filling fraction is large.Applying an oscillating shear field,the thermal conductivity of the composite material increases slightly.(3)Then we grafted the MoS2 surface.Both the grafting density and grafting length will affect the thermal conductivity of the composite material,and the greater the grafting density and the longer the grafting length,the more obvious the thermal conductivity of the composite will decrease.Although the introduction of graft chain can improve the affinity of the two materials,the two-dimensional structure of the filler is destroyed,so the mechanical properties of the material are reduced.3.Thermal conductivity of PDMS/BN/MoS2 compositesTo reduce the influence of cavity inside the material caused by the addition of MoS2 filler,in this section,we explored the impact of the joint action of BN and MoS2 filler on the thermal conductivity of systems.The results indicate that with the same filling fraction,compared with a single filler,the combined use of the two fillers effectively improves the dispersion of the two-dimensional packing,and the thermal conductivity is improved more obviously,and there is an optimal ratio between the two fillers.Studies have found that the increase in thermal conductivity of PDMS/BN/MoS2 is caused by the decrease in the volume fraction of holes(?)inside the materials.In addition,the thermal conductivity of PDMS/BN/MoS2 composites will also improve with the increase of the hybrid BN/MoS2 filler fraction.The application of oscillating shear also improves the thermal conductivity of PDMS/BN/MoS2 composites.