Effect of Deep Eutectic Solvent on the Graphitization and Thermal Properties of Polyimide Films

Overheating of electronic devices reduces lifespan and increases safety risks. The use of graphite films with high thermal conductivity to enhance thermal dissipation in electronic equipment is of significant importance. This study used urea-choline chloride (UCC) to modify polyimide (PI) films from two different monomer systems, which were then graphitized to prepare a novel graphite film with high thermal conductivity. The direct formation of hydrogen bonds between poly(amic acid) (PAA) and UCC facilitates the ordered structure during thermal imidization, enhancing the graphitization degree and thermodynamic properties of PI films. The results indicate that the graphitization degree of PI films increased from 30% to over 59% in the 4,4′-oxydianiline-pyromellitic dianhydride (OPU) system and from 80% to over 92% in the 4,4′-diaminobenzoyltiphenylamine-3,3′,4,4′-biphenyl tetracarboxylic dianhydride (DBU) system. Notably, 4,4′-oxydianiline-pyromellitic dianhydride-3.5 wt% urea-choline chloride (OPU35) and 4,4′-diaminobenzoyltiphenylamine-3,3′,4,4′-biphenyl tetracarboxylic dianhydride-3.5 wt% urea-choline chloride (DBU35) exhibited the highest thermal conductivity in their respective systems, with coefficients of 45 and 742 W/m K, representing 200% and 47.8% improvements over pure PI-based graphite films. This provides a new material for heat dissipation in electronic devices.