Disentangling PVA-Induced Densification and Ag-Nanoparticle Phonon Bridging in Boron Nitride Nanosheet/Aramid Nanofiber Composite Films for Thermal Transport.
Abstract
Efficient heat dissipation in polymer-based films is increasingly important for modern electronic devices, yet thermal transport is often limited by insufficient structural compactness and pronounced interfacial thermal resistance. Herein, boron nitride nanosheets (BNNSs) were exfoliated from hexagonal boron nitride (h-BN) by ball-milling and subsequently integrated with aramid nanofibers (ANFs) to form thermally conductive composite films. To regulate heat-transfer pathways, poly(vinyl alcohol) (PVA) was introduced to densify the layered architecture and promote horizontal orientation of BNNSs, while silver nanoparticles (Ag NPs) were anchored onto BNNSs to construct interfacial phonon bridges. Compared with the ANF/BNNS film, which exhibited an in-plane thermal conductivity of 22.05 W·m-1·K-1, PVA incorporation increased the value to 28.04 W·m-1·K-1 for ANF-PVA1/BNNS, whereas Ag modification afforded a maximum of 27.11 W·m-1·K-1 for ANF/BNNS-Ag2. Structural analyses revealed that PVA reduced film thickness and enhanced BNNS orientation through strong hydrogen-bonding interactions, while Ag NPs improved interfacial thermal coupling at moderate loading but introduced additional phonon scattering at excessive contents. Notably, the combined use of PVA and Ag NPs did not yield further enhancement, and the optimal dual-modified film, ANF-PVA1/BNNS-Ag2, reached a thermal conductivity of 26.94 W·m-1·K-1. This result indicates that thermal transport in BNNS-based composite films is governed by a balance among densification, BNNS content and orientation, interfacial interactions, and phonon scattering. Infrared thermal imaging of LED heat-spreading tests further corroborated the thermal conductivity results. This work provides a nuanced understanding of densification and phonon-bridge engineering for the rational design of thermally conductive composite films.