Preparation And Performance Research Of Highly Thermally Conductive And High Flexible Thermal Gel

With the development of electronic technology,the electronic components show a trend of high power density and small volume,and the heat generated by them increases rapidly.Thermal management is important for electronic components.Because there is a certain roughness on the surface of the electronic components and the heat spreader,the two surfaces are not suitable and the gap between the two surfaces would be filled by the air with lower thermal conductivity,which eventually leads to unsatisfactory heat dissipation.Nowadays,the efficiency of heat dissipation has been improved by placing thermal interface materials between the electronic component and the heat spreader in industrial communities.Compared with other thermal interface materials,the thermal gel has excellent fluidity and high thermal conductivity which is a hot research topic in the field of thermal interface materials.Although there has been some research progress in thermal gels,it is still difficult to meet the requirements of heat dissipation for electronic components.In this paper,highly thermally conductive and flexible thermal gels were prepared by hydrosilylation reaction where spherical aluminum powder and zinc oxide were used as thermally conductive fillers,while vinyl silicone oil and hydrogen-containing silicone oil were used as substrates.The main research contents were as follows:（1）It was based on the network structure of thermal gel to regulate its mechanical properties and thermal conductivity.It was an effective method that increasing the filler loading fraction to improve the thermal conductivity of thermal gels,but it would improve its modulus and reduce its flexibility.To address that problem,we regulated the network of thermal gel based on functional groups of silicone rubber.On the one hand,the crosslink density was regulated with the adjustment of the ratio of Si-Vi to Si-H.The data shows that the higher the ratio,the higher the elongation at break.On the other hand,the crosslink density was regulated with the adjustment of the ratio of the Si-H bond ratio of double-ended hydrogen-containing silicone oil as the chain extender to hydrogen-containing silicone oil（side-chain type）as the crosslinking agent.The higher the ratio of the Si-H bond of chain extender to crosslinker,the lower the crosslink density of the thermal gel and the higher the elongation at break.However,the ratio of Si-Vi to Si-H and the Si-H bond ratio of chain extender to crosslinker cannot be too large,otherwise,the thermal gels could not be cured.Therefore,when the filler loading fraction is 90 wt%,the ratio of Si-Vi to Si-H in the silicone rubber matrix is2:1,and the Si-H bond ratio of chain extender to crosslinker is 1.5:1,the thermal gel has the best comprehensive performance:the viscosity is 254.0 Pa·s and the thermal conductivity is 4.3 W·m^-1·K^-1 while the elongation at break is 114.0%which is higher than other reported thermal interface materials.（2）It was based on the molecular structure of silicone rubber to regulate mechanical properties and thermal conductivity of thermal gels.It was hopeful to improve the efficiency of heat dissipation by reducing the modulus because the thermal contact resistance of the thermal interface materials decreases with the decreased modulus of the thermal interface materials.To address that problem,we studied the grafting rate for dangling chains on the comprehensive performance of thermal gels using vinyl silicone oil as the backbone and single-end hydrogen-containing silicone oil as the dangling chain which could play a role of internal plasticization.The research data shows that modulus decreases and thermal contact resistance decreases with the increment of grafting rate.When the grafting rate is 98%,the thermal gel has low thermal contact resistance which was 47%lower than that of the ungrafted.In addition,we studied the effect of filler loading fraction on the mechanical properties and thermal conductivity of thermal gels.It is found that the elongation at break of the thermal gel increases and then decreases with the increment of filler loading fraction while the thermal conductivity increases with the increment of filler loading fraction.When the grafting rate is 98%and the filler loading fraction is 90 wt%,the prepared thermal gel has the best comprehensive performance with low thermal contact resistance,high thermal conductivity,and high flexibility:the viscosity is 297.0 Pa·s while the elongation at break is 104.1%and the thermal contact resistance is only 0.9 K·cm²·W^-1 when the thermal conductivity is 4.7·W·m^-1·K^-1 which is superior compared with other reported thermal interface materials.In addition,the thermal gels perform well in the dispensing test,tensile cycle test,heat dissipation test for chip,and power cycle test.