Phase-Transition-Driven Thermomechanical Regulation of Thermal Interfaces

Thermal interfaces are often limited by imperfect real contact, where surface asperities and interfacial gaps can dominate the overall thermal resistance. Here, we develop a flexible phase-change composite (FPCC) that couples the solid-liquid transition of n-docosane with mechanical softening, expansion-generated normal loading, and interfacial reconfiguration to regulate thermal contact. The composite integrates n-docosane within a compliant styrene-ethylene-butylene-styrene (SEBS) matrix supported by an interconnected expanded-graphite (EG) scaffold. The optimized FPCC exhibits a thermal conductivity of 5.18 W m-1 K-1 and a latent heat of 153.5 J g-1. Across the phase transition, the tensile modulus decreases to ∼0.60 MPa, while expansion under interfacial constraint generates a normal stress exceeding 40 kPa (∼5.8 psi). An equivalent-pressure analysis based on the measured Rcontact-P relationship indicates that a pressure increment of ∼5.8 psi corresponds to an approximately 54% reduction in contact thermal resistance from the 5 psi reference condition. Frequency-domain thermoreflectance measurements further reveal an increase in effective contact conductance from 2.32 to 8.99 MW m-2 K-1 across the transition, while synchronized mechanical-thermal measurements show reproducible co-evolution of normal loading and conductance during repeated cycling. The enhanced contact state is partially retained after cooling, indicating that repeatable thermomechanical modulation operates together with partially retained interfacial reconfiguration. In LED cooling, the FPCC lowers the device temperature by up to 6.5 °C relative to a commercial thermal pad. These results establish phase-transition-driven thermomechanical regulation as a route to improving and stabilizing low-preload thermal interfaces through the coupled effects of compliance, expansion-generated loading, and interfacial reconfiguration.