Construction of tree-ring mimetic 3D networks in polyvinyl alcohol/boron nitride composites for enhanced thermal management and mechanical properties

Constructing a three-dimensional (3D) filler network in polymer thermal interface materials (TIMs) is crucial for enhancing thermal conductivity and mechanical properties. However, the discontinuous and loose network of fillers are one of the main reasons hindering the joint improvement of thermal conductivity and mechanical properties. The construction of a regular and dense 3D continuous filler network remains a significant challenge. In this study, an innovative bidirectional freezing technique was designed to create a polyvinyl alcohol (PVA)/boron nitride (BN) composite with a tree-ring-like 3D network. This technique promotes the formation of 3D network consisting of long-range lamellar BN layers with a tree-ring-like structure by controlling the nucleation and growth of ice crystals along the bidirectional temperature gradient induced by a polytetrafluoroethylene (PTFE) cone. The resulting PVA/BN composite exhibits high thermal conductivity (6.25 W/m·K) due to the lower interfacial thermal resistance between fillers (1.271 × 10⁻⁷ K m²/W), and an enhanced tensile strength of 41.71 MPa, which is attributed to the regular and dense BN network. This study presents a feasible strategy for constructing a 3D continuous network structure in polymer-based TIMs, paving the way for advancements in thermal management solutions.