| The heat dissipation requirements of devices are increasingly strict with the intensive integration of electronic devices and the increase in power consumption of equipment.It is necessary to dissipate the heat generated by the equipment through thermal conductive materials in time to ensure the normal operation of the equipment.Although the existing industrial thermal conductive materials have excellent thermal conductivity,the composites sacrifice other properties and cannot be really applied in some practical fields because of the high filling fraction.Therefore,it is necessary to prepare thermal conductive materials with excellent thermal conductivity,high insulation and good mechanical properties.In this work,the thermal conductivity silicone rubber was prepared by chemical modification of the filler,three-dimensional network structure was constructed by using different dimensions fillers and vertical orientation of the filler in the matrix.The composites had excellent thermal conductivity while maintaining good insulation,mechanical properties and low hot loss.Firstly,silicon carbide(SiC)and boron nitride(BN)were modified by chemical modification,and a layer of polycatechol/polyamine(PCPA)coating was formed on the surface of the filler.Meanwhile,silane coupling agent was used for grafting and then the silicone rubber(SR)composites were prepared.Effect of two modified fillers on properties of the composites was also studied.Results show that the thermal conductivity of the composites with modified fillers(modified SiC(m SiC)and modified BN(m BN))is higher than that of the composites with unmodified fillers.The thermal conductivity of r SR/100m BN composites is 1.26 W·m-1·K-1 when the loading of m BN is 100 phr,which is 26%higher than that of r SR/100BN composites and 61.5%higher than that of r SR/100m SiC composites.Meanwhile,when the ratio of m SiC to m BN is 1:9,the thermal conductivity of r SR/m SiC/m BN composites is 1.35 W·m-1·K-1,which is higher than that of the composites filled with only one type of filler.In addition,the composites have high insulation and excellent temperature resistance.Two-dimensional layered BN and three-dimensional irregularly shaped SiC were used to combine with one dimensional tubular carbon nanotubes(CNT),respectively.The properties of the composites with different CNT contents were studied.Results show that when the content of CNT is low,the thermal conductivity of the composites with BN or SiC is not significantly improved.When the content of CNT is further increased,the three-dimensional thermal network of BN and CNT in the matrix is effectively constructed.When the loading of BN is 80 phr and the content of CNT is 1wt%,the thermal conductivity of the composites reaches 1.89 W·m-1·K-1 and the insulation and mechanical properties of the composites are also maintained.In addition,the relationship between the photothermal properties and thermal conductivity of the composites containing CNT is also discussed.Results show that the effective combination of photothermal properties and thermal conductivity can be guaranteed only when the ratio of BN to CNT is in an appropriate range.In order to further improve the thermal conductivity of the composites in the vertical direction,the oriented BN was prepared by mechanical shearing and folding,and CNT and SiC were introduced to prepare the thermal composites.Results show that BN tends to be vertically arranged in the matrix,the presence of CNT and SiC fillers with different dimensions enables effectively and rapidly construct a three-dimensional thermal conductive network and improve the thermal conductivity of the composite in the vertical direction.When the loading of BN is 80 phr and the content of CNT is1wt%,the thermal conductivity of the composites is 2.4 W·m-1·K-1,which is 40.62%higher than that of the composites without perpendicular arrangement of BN and 12times that of ordinary silicone rubber.Meanwhile,the composites have favorable mechanical and temperature resistance properties. |
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