Immiscible Binary Organic Phase‐Change Composites with Segregated h‐BN Networks for Advanced Thermal Management

The development of thermally conductive and leakage‐resistant phase‐change materials (PCMs) for next‐generation electronics remains a major challenge in the development of thermal interface materials (TIMs). Herein, a simple and scalable strategy is reported for the fabrication of a multifunctional PCM composite (PPB30) by combining two immiscible organic PCMs, paraffin wax (PW) and poly(ethylene glycol) (PEG), with thermally conductive hexagonal boron nitride (h‐BN) particles. Through simple melt mixing, the ternary composite formed a particle‐stabilized emulsion, in which h‐BN selectively localized at the PW‐PEG interfaces, spontaneously creating a segregated filler network without the use of surfactants, encapsulation, or complex processing. The resulting composites exhibit outstanding thermal conductivity (>20 W m −1 K −1 ), robust shape stability, reprocessable adhesion, and tunable latent heat capacity. Structural analysis and Lewis‐Nielsen modeling confirmed that immiscibility‐driven filler segregation facilitated continuous thermal pathways. Importantly, the composites are readily prepared by simple, low‐temperature melt mixing of commercially available materials. In practical CPU cooling tests, PPB30 significantly reduced the peak operating temperatures compared with commercial TIM pastes, while also providing thermal buffering via latent heat absorption. These findings demonstrate that PPB30 offers a cost‐effective, multifunctional, and process‐ready TIM platform for efficient and stable thermal management of high‐power electronic systems.