Investigation On Thermal Conductivity Of Silicone Organic Composites Filled With Silicone Rubber,Carbon Fiber And Alumina

With the heat generation of electronic devices increasing,thermal interface materials have played an important role in heat dissipation and the normal operation of electronic devices.Commonly used thermal interface materials are mainly composites filled with polymer matrix and high-thermal-conductive fillers.In this paper,thermal interface materials are prepared by carbon fiber,alumina and silicone rubber.In order to improve the thermal conductivity of the composites effectively,three parts have been included in this paper.Firstly,in order to explore the synergistic effect of two-dimensional and zero-dimensional fillers,spherical alumina of different radius and carbon fiber were co-filled into silicone rubber in this experiment.The results show ed that the composites with carbon fiber filled had a large viscosity increase at the percolation threshold(20vol%),the same as the electrical conductivity,but there was not obvious sudden rise at the thermal conductivity.When the total content of the co-filling is 20vol%,there appeared an obvious synergy effect in thermal conductivity between 3 ?m spherical alumina and carbon fibers;but there is no significant synergistic effect when the total amount of co-filling is 40vol%.The results also showed that synergy effect of the composites have a large relationship with the particle size of alumina,and 3 ?m spherical alumina had a better synergistic effect than 500 nm on thermal conductivity,while 20 ?m spherical alumina has no synergistic effect.Secondly,in order to build a more efficient thermal network,this experim ent used mechanical extrusion method to orient carbon fiber to explore the effectiveness and influencing factors of oriented fibers on thermal conductivity.The results showed that the single-filled and co-filled carbon fiber orientation all made carbon fiber well oriented along the axial direction,and the thermal conductivity along the axial thermal was increased by 30% and 50% respectively.In the co-filled oriented carbon fiber composites,the addition of small amount of alumina particles could increase the viscosity of the material system with low filler content,to promote the orientation of the carbon fibers,but it had little effect on the thermal conductivity of carbon fiber system with higher filler content.Thirdly,in order to improve the interfa cial state of carbon fiber and alumina in silicone rubber,this experiment used spray drying method to prepare combined fillers,like a "mace stick",in which alumina particles was bonded to surface of carbon fiber.The composites with combined fillers filled had higher thermal conductivity than the composites with untreated fillers,and the thermal conductivity is gradually enhanced with the increase of the content.Also,the stability of the combined filler structure in the composites lead to good hightemperature stability of treated composites.The theoretical analysis with the effective medium theory showed that the combined filler sample system possessed lower interfacial thermal resistance than the untreated filler sample system,and the interface thermal resistance in combined filler system decreases with the adding of the fillers,which promoted the thermal conductivity of the thermal interface material continuously.