Surface modification of graphite and its effect on thermal and mechanical properties of graphite-based thermal interface materials

Graphite has been widely used in the preparation of polymer-based thermal interface materials with excellent performance due to its high thermal conductivity. However, there is a huge difference in the surface energy between graphite and polymer matrix, which can lead to the aggregation of graphite powder in the composite system. Because of the agglomeration, the thermal transport paths in the thermal interface materials are blocked. The main strategy to solve such a problem is to perform surface modification on graphite, which can improve the dispersion of graphite and build more transfer paths. In this work, the graphite was hydroxylated by oxidation firstly, then the dodecyl trimethoxy silane, hexadecyl trimethoxy, and titanate coupling agent were grafted onto the graphite surface by wet modification. Then, the thermal interface material was prepared by adding original and modified graphite in the polymer, and their thermal and mechanical properties were studied and compared. Experimental results showed that the thermal properties of the two groups had no significant difference. With the graphite content increasing from 45 wt.% to 60 wt.%, the thermal conductivity increased from 11 W/(m.K) to 21.5 W/(m.K). After three cycles of compressions, the stress of modified samples was smaller under the same strain. This means that the modified sample has better compression resilience and can work more stably under certain cyclic compression. This work provides important information for the surface modification of graphite to improve its thermal and mechanical behaviors in thermal interface materials.