Directional ANF/BN Porous Scaffolds via Sequential Freeze Casting

The increasing power density and miniaturization of electronic devices require thermal management materials that can efficiently dissipate localized heat. Polymer-based composites are attractive because of their low density and processability, but their heat transport is often limited by discontinuous filler networks and interfacial thermal resistance. Herein, we propose a sequential freeze-casting strategy to fabricate hierarchical porous aramid nanofiber (ANF)/boron nitride (BN) scaffolds for thermal management applications.

An ANF solution was first directionally frozen to construct a porous polymer framework. The frozen structure was stabilized by gelation in an AcOH/EtOH mixed solvent, followed by solvent exchange and freeze-drying. A BN/poly(vinyl alcohol) (PVA) suspension was then introduced into the ANF scaffold, and a second unidirectional freeze-casting step was performed to form a secondary BN-based porous network. SEM observations confirmed directionally aligned pores in the ANF scaffold and porous BN/PVA structures produced by ice templating.

To optimize BN network stability, the PVA content was varied from 1 to 10 wt% at a fixed BN loading. The 1 wt% PVA sample failed to maintain its structure after freeze-drying, whereas the 10 wt% PVA sample showed wall cracking. In contrast, the 4 wt% PVA condition retained the initial shape with minimal drying-induced deformation, indicating a suitable balance between binder content and scaffold integrity.

This work demonstrates the feasibility of constructing a dual-network ANF/BN porous scaffold through sequential freeze casting. The designed architecture provides filler-rich pathways and open pores that may be further utilized for phase change material impregnation. Therefore, this hierarchical scaffold design offers a promising structural platform for thermal spreading and heat-buffering thermal management composites.