Application Of Graphene Prepared By Supercritical Carbon Dioxide Method In Polymer Based Thermal Interface Materials

Since the 21st century,the electronic industry has developed rapidly.Moore’s Law states that the number of transistors on an integrated circuit will double every 18 months.The increasing number of transistors produce a large amount of heat,which often results in the damage of electronic devices due to high temperature.Therefore,the development of more efficient thermal management materials is very important for the microelectronics.This work focused on the study of polymer based thermal interface materials,adding graphene into the polyvinylidene fluoride(PVDF)matrix to prepare composite materials with higher thermal conductivity.The thermal conductivity of composites was further improved by promoting the dispersion of graphene,the interfacial compatibility between graphene and the polymer matrix and the preparation method.Firstly,the graphene with high aspect ratio and less defect was obtained via supercritical CO2 method combined with mechanical peeling possess.The composites were prepared by solution blending method.At the same time,the introduction of polyvinylpyrrolidone(PVP)as a "crosslinking agent" can not only improve the dispersion of graphene,but also enhance the interaction between graphene and the polymer matrix by non-covalent bonding.The experimental results showed that the addition of graphene can increase the crystallinity of the composite materials,which was conducive to heat transfer.When the graphene load reached 10wt.%,the thermal conductivity of the composite reached 3.48 W·m-1·K-1,which was 14.5 times that of the original polymer.This was because the graphene load reached the threshold and formed effective heat transfer paths,which was conducive to the rapid transfer of heat.Furthermore,the addition of graphene improved the thermal stability of the polymer,and the composite materials were still electrically insulated.Then,through surface modification of graphene,the molecular interaction between graphene and polymer can be further enhanced.After surface modification of graphene with polydopamine,the thermal conductivity of the composite material reached 4.47 W·m-1·K-1 when the modified graphene load was 10wt.%,which was 28%higher than the previous composite.In addition,after surface modification of PDA,the graphene changed from hydrophobic to hydrophilic.By using electrospinning method and freeze-dried casting method,more effective heat transfer network structures were constructed.The application of external force made the graphene can be arranged in a directional way rather than random distribution,and graphene can be more fully utilized to form more heat transfer paths.The thermal conductivity of the composites prepared by electrospinning method and freeze-dried casting method were 6.3 5 W·m-1·K-1 and 6.58 W·m-1·K-1,respectively,which were 42%and 47%higher than the composite prepared by solution blending method.Moreover,the thermal conductivity of the composites was less affected by temperature due to the heat transfer network structure.The actual heat dissipation effect of the composites was tested by infrared thermal imager,and the results showed that the heat transfer performance of the composites had been greatly meliorated by the improved preparation methods.