Ordered Alignment of Liquid Crystalline Graphene Fluoride for Significantly Enhancing Thermal Conductivities of Liquid Crystalline Polyimide Composite Films

Abstract

The low thermal conductivity coefficient (λ) of polyimide (PI) films are limiting their application in high-power electronic equipment, and the disordered alignment of fillers discourage efficient improvement of λ for PI-based composite films. Herein, polyethylene glycol trimethylnonyl ether is used to perform liquid crystalline modification on graphene fluoride (LC-GeF) to achieve ordered alignment. Intrinsically thermally conductive liquid crystalline PI (LC-PI) matrix is utilized to fabricate thermally conductive LC-GeF/LC-PI composite films. In-plane λ (λ∥) and through-plane λ (λ⊥) of 15 wt % LC-GeF/LC-PI composite films reach 4.21 and 0.63 W/(m·K), 446.8% and 320.0% higher than λ∥ (0.77 W/(m·K)) and λ⊥ (0.15 W/(m·K)) of normal PI films, 99.5% and 96.9% higher than λ∥ (2.11 W/(m·K)) and λ⊥ (0.32 W/(m·K)) of LC-PI films, also higher than 15 wt % GeF/LC-PI composite films. Additionally, LC-GeF/LC-PI composite films possess more excellent insulating, mechanical, and thermal properties than GeF/LC-PI composite films.