Preparation And Properties Of Natural Rubber-based Composites For Thermal Interface Material Applications

With electronic devices towarding to the miniaturization,high integration and multi-functionality,the heat dissipation issue is facing the severe challenges.How to manage heat generated by them effectively is very critical to the operational reliability and lifetime for electronic devices.Thus,it is one of the most urgent tasks to pursue and prepare novel polymer-based composites with high thermal conductivity and good insulation in the field of electronic packaging materials.Thermal interface materials(TIMs),as an important branch of thermal management materials,play an important role in the heat dissipation.Recently,natural rubber(NR)has gained uniquely favour in the application of TIMs due to its excellent mechanical properties,electrical insulation and high elastic properties.The good flexibility of the NR can meet the different shapes of interfaces.Also,the compressible deformation can form a good contact between the heat sink and the heat source,transferring the heat into surrounding environment.However,the thermal conductivity of NR is only about 0.2 W m-1 K-1,which due to the effect of random entanglements at the ends of macromolecular chains,large molecular weight and polydispersity.Therefore,it is necessary to add highly thermal conductive filler to improve the thermal conductivity of TIMs.There are many factors to affect the thermal conductivity of polymer-based TIMs,which not only include the filler size,content,and structure,but also the phonon scattering and interfacial thermal resistance between different kinds of fillers as well as filler and polymer matrix.Therefore,how to reduce the influence as above mentioned to prepare highly thermal conductive polymer-based TIMs have become the latest research hotspots.This paper has mainly studied how to reduce phonon scattering and interface thermal resistance between different kinds of fillers as well as filler and polymer matrix.The specific contents are as follows:(1)Thiol-functionalized BN was prepared by the ball milling and surface modification method,namely BN-SH.BN/NR thermal interface composites with three-dimensional thermal network structures were prepared by the ice-template method.The-SH functional groups on the edge or surface of BN can not only promote the vulcanization of NR,but also help the connection between BN filler and NR matrix,reducing the interface thermal resistance of its composites.In addition,the three-dimensional thermal network structures of the filler also plays an important role in improving the thermal conductivity.The experimental results show that when the content of BN-SH is 25 wt%,the BN/NR thermal interface composites with a three-dimensional thermal network structure has the largest thermal conductivity of 0.79 W m-1 K-1.(2)The chemical surface modification method,chemical reaction method and ice template method were used together to prepare the three-dimensional BN/rGO thermal conductive network skeleton with covalent bond connections.Additionally,the vacuum-assisted infiltration method was also used to prepare BN/rGO/NR TIMs.The filler of BN and rGO are connected by the covalent bonds,which effectively reduce the phonon scattering and interfacial thermal resistance.The three-dimensional thermal network structures constructed also promotes the formation of continuous and effective heat transfer pathways.The results show that when the mass ratio of BN and rGO is 4:1 as well as filler contents are 4.9 vol%,the BN/rGO/NR TIMs with covalent bond connections and three-dimensional thermal network structures possesses the largest out-of plane thermal conductivity 1.28 W m-1 K-1.(3)BN/CNTs thermally conductive hybrids with covalent bond connections were prepared by chemical surface modification and chemical reaction method.Fabrating the BN/CNTs/NR TIMs with three-dimensional layered structures by the vacuum-assisted infiltration method.Through constructing covalent bond connections,the phonon scattering and interface thermal resistance between two different dimensions of BN and CNTs are reduced.The three-dimensional layered structure of BN/CNTs hybrids in the NR also improve interface condition between filler and NR matrix,thus forming an effective continuous and stable heat conduction pathway finally.The results demonstrate that when the mass ratio of BN and CNTs is 8:1 and filler content is 12 wt%,the BN/CNTs/NR TIMs with covalent bond connections and three-dimensional layered structures have the largest out-of plane thermal conductivity,the value is 1.34 W m-1 K-1.(4)Using the chemical surface modification and carbonization method to prepare BN/Lignosulfonate thermal conductive hybrids.BN/Lignosulfonate/NR TIMs with three-dimensional layered structure are prepared by the vacuum-assisted infiltration method.The carbonization process turns lignosulfonate into a certain degree of graphitization carbon from an amorphous structure,leading to reducing the phonon scattering and improving the thermal conductivity of TIMs.Meanwhile,the formation of C-N covalent bonds also significantly degrade the interface thermal resistance between BN and Lignosulfonate.In addition,the formation of three-dimensional layered filler structures in the matrix not only increases its contact with NR matrix,but also benefit to reduce the interface thermal resistance,which create favorable conditions for preparing highly thermal conductive BN/Lignosulfonate/NR TIMs.The results indicate that when the mass ratio of BN and lignosulfonate is 4:1 and filler content is 25 wt%,the thermal conductivity of carbonized BN/lignosulfonate/NR TIMs reache a maximum of 1.17 W m-1 K-1.