Spatial Confinement Pressing Induces Directional SCF Assembly for Low‐Filler Flexible Thermally Conductive PDMS ‐Based Composites

Driven by device miniaturization and ultra‐high integration, thermal management faces critical challenges. Conventional polymer composites exhibit low intrinsic thermal conductivity, and high filler loading inevitably compromises the mechanical properties of the matrix, thereby restricting their practical engineering applications. This work develops a spatial confinement hot‐pressing strategy to fabricate ultrathin high‐performance thermally conductive composite films. Homogeneous slurries are prepared via high‐speed homogenization, in which 5 wt% liquid ethylene propylene diene monomer (EPDM)‐modified polydimethylsiloxane (PDMS) serves as the flexible matrix and short‐cut carbon fibers act as the thermal conductive filler. High‐intensity shearing effectively alleviates filler agglomeration. Combined with spatial confinement and hot‐pressing treatment, the thermal conductive fillers are directionally rearranged to construct continuous and dense thermal conduction networks. EPDM remarkably improves the processability, flexibility, and interfacial compatibility of the composite system. Experimental results indicate that the composite containing 25 wt% short‐cut carbon fibers (SCF) maintains a stable temperature of 70°C under a high heat flux of 30 W·cm −2 , and its heat dissipation efficiency is 71.4% higher than that of commercial thermal interface materials. Furthermore, the material exhibits excellent long‐term operational stability after 100 thermal cycles, demonstrating promising prospects for practical thermal management applications.