Hierarchical micro-nanofiber networks in poly(p-phenylene benzobisoxazole) fibrous films enabling high mechanical strength and thermal conductivity

Acidity-regulated partial-protonation enables surface-selective nanofibrillation of PBO fibers while preserving the microfiber skeleton. • Hierarchical PBO films achieve synergistic enhancement of mechanical strength (267.55 MPa) and thermal conductivity (24.80 Wꞏm −1 ꞏK −1 ). • Hierarchical PBO film as a heat spreader lowers hotspot temperature by 12.2 °C and homogenizes temperature field. • One-step dissolution-to-film process reduces preparation time by nearly 7.5-fold and enables scalable blade-coating/roller-pressing fabrication. Advanced thermal-management materials require thin films that combine high thermal conductivity with robust mechanical properties. Poly( p -phenylene benzobisoxazole) (PBO) nanofibers are promising candidates; however, conventional top-down processing in strong protic acids requires complete fibrillation followed by deprotonation and reassembly through a multistep sol-gel-film route, which disrupts the native fibrous hierarchy and limits both mechanical performance and processing efficiency. Herein, we report an acidity-regulated partial-protonation strategy that induces interface-selective fibrillation and enables the fabrication of hierarchical PBO micro-nanofiber films through direct dissolution-to-wet-film filtration followed by hot pressing. The resulting highly oriented and compact network consists of retained microfibers that form continuous load-bearing and heat-transport pathways, while surface-exfoliated nanofibers act as intrinsic binders to bridge adjacent microfibers. The optimized hierarchical film achieves a tensile strength of 267.55 MPa, 40.83% higher than that of the fully dissociated PBO nanofiber film, together with an in-plane thermal conductivity of 24.80 W m −1  K −1 . Meanwhile, the direct route substantially shortens the solution-to-wet-film processing time compared with conventional sol-gel processing. As a heat spreader, the film homogenizes the temperature field, suppresses local hotspots, and reduces the hotspot temperature by 12.2 °C. Furthermore, integration with blade coating and roller pressing demonstrates its compatibility with continuous film fabrication, highlighting the potential scalability of this filler-free and structure-preserving strategy for advanced thermal-management applications. This work presents an acidity-regulated partial-protonation strategy to fabricate micro-nano hierarchical PBO fibrous films via interface-selective fibrillation engineering. By tuning solvent acidity, surface-exfoliated nanofibers act as intrinsic binders while retained microfibers serve as continuous scaffolds, synergistically enhancing films' mechanical and thermal performance: in-plane thermal conductivity of 24.80 W·m −1 ·K −1 , tensile strength of 267.55 MPa, and thermal stability (T 5%  ≈ 596 °C). Download: Download high-res image (188KB) Download: Download full-size image