Flexible Form-Stable Phase Change Materials with a Thermally Conductive Network Constructed by Differently Sized Expanded Graphite for Thermal Interface Applications

Growing demands for high power density and miniaturization in electronic devices require high-performance thermal interface materials that can lower the interfacial thermal contact resistance (TCR) and enable efficient thermal management of flexible electronics. Herein, flexible form-stable phase change materials (FCPCMs) were developed using paraffin wax (PW) as the phase change energy storage unit and a styrene–ethylene/butylene–styrene block copolymer (SEBS) to construct a three-dimensional crosslinked network; an organic peroxide (BIPB) initiated the crosslinking reaction to stabilize the structure, ensuring that the FCPCMs retain good shape stability and leakage resistance above the phase change temperature. Expanded graphite (EG) and ultrasonicated expanded graphite (UEG) were further introduced to synergistically construct thermally conductive channels and thereby enhance the thermal conductivity of the FCPCMs. The optimal FCPCM achieved a thermal conductivity of 2.39 W/(m·K), 8.24 times that of PW. The prepared FCPCMs showed no obvious decay in phase change temperature or latent heat after 200 cycles, demonstrating good thermal reliability and cycling stability. In addition, owing to the crosslinked network, the material exhibits self-healing and adaptive capabilities upon heating and can effectively fill microscopic defects. In a chip heat dissipation test, combining the material with a heat sink lowered the chip surface temperature at 12 W from 132.9 °C to 68.7 °C (a reduction of 48.3%) and reduced the surface temperature difference from 14.5 °C to 2.1 °C (a reduction of 85.5%) relative to the blank group, demonstrating excellent thermal management performance. This effectively suppressed thermal contact resistance and provided an approach to chip thermal management.