Molecular Brush-Grafted Liquid Crystalline Hetero-Structured Fillers for Boosting Thermal Conductivity of Polyimide Composite Films

Hetero-structured thermally conductive fillers, benefiting from the low interfacial thermal resistance and fillers’ synergistic effect, have been proven to be the ideal choice for improving the thermal conductivities of polymer composites. However, hetero-structured fillers are usually disorderly distributed in the polymer matrix, hindering the further improvement of the efficiency of constructing thermal conduction pathways in polymer composites. This work proposes a new strategy to graft polymethyl methacrylate molecular brushes on the surfaces of fluorinated graphene@carbon nanotube (FG@CNT) hetero-structured thermally conductive fillers by atom transfer radical polymerization. FG@CNT is orderly arranged and presents the liquid crystalline state (LC-(FG@CNT), which is then introduced into the liquid crystalline polyimide (LC-PI) matrix with high intrinsic thermally conductivity to fabricate LC-(FG@CNT)/LC-PI thermally conductive composite films. The in-plane and through-plane thermal conductivities (λ_∥, λ_⊥) of 15 wt.% LC-(FG@CNT)/LC-PI films reach 5.66 and 0.76 W·m⁻¹·K⁻¹, respectively, which are 168.2% and 137.5% higher than those of the LC-PI films (λ_∥ = 2.11 W·m⁻¹·K⁻¹, λ_⊥ = 0.32 W·m⁻¹·K⁻¹), also significantly higher than those of 15 wt.% FG@CNT/LC-PI composite films (λ_∥ = 4.72 W·m⁻¹·K⁻¹, λ_⊥ = 0.74 W·m⁻¹·K⁻¹). Demonstrated by heat dissipation testing and finite element simulation, the LC-(FG@CNT)/LC-PI composite films show excellent thermal management capabilities and great application potential in the new generation of flexible electronic devices.