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With the rapid development of portable electronic devices, there is an urgent need for the multifunctional composites like excellent electromagnetic interference (EMI) shielding performance, mechanical property, and thermal management capabilities. Here, due to the low thermal conductivity of phase change materials (PCMs), a sandwich structure carbon nanotube/phase change microcapsule/carbon nanotube (CNT/PMC/CNT (CPC)) film was prepared by vacuum‐assisted filtration (VAF) method. CNT, PMC, and cellulose nanocrystal (CNC) were used as functional fillers. The addition of CNCs was used to improve the mechanical performance of CPC film. Compared with PMC‐CNC (PC) film, CPC film with sandwich structure prevented leakage phenomenon efficiently. Subsequently, the use of ultrasonic‐assisted forced infiltration (UAFI) successfully infiltrated polydimethylsiloxane (PDMS) matrix in the filler skeleton to obtain CNT/PMC/CNT/PDMS (CPCP) composites. When filler mass ratio (CNT: CNC and PMC: CNC) reached 10:1, the thermal conductivity of CPCP composites was 2.32 W/(m·K) and total EMI shielding effectiveness (EMI SET) of it with 0.38 mm thickness reached 37.46 dB at 12.4 GHz. Besides, these sandwich composites exhibited the good mechanical properties and heat storage capacity. And we systematically observed the impact of different addition amounts of PC homogeneous dispersing solution on phase change ability of CPCP10:1 composites. In summary, CPCP phase change composites with sandwich structure shows potential application prospect in thermal management materials with EMI shielding of electronic devices. Highlight: The sandwich structure CPCP composites prepared by the combination of VAF and UAFI method, showing superior thermal conductivity and phase change ability.CPCP has excellent EMI shielding performance, which can meet the need of TMMs with EMI shielding performance.Compared with same thickness PC film, sandwich CPC film can prevent leakage phenomenon efficiently. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) have been widely used in passive thermal management and energy storage due to their high latent heat capacity. However, the low thermal conductivity and leakage problems of PCMs are two bottlenecks for its application in the field of heat-related applications. Although many present studies can tackle one or two of these problems by preparing phase change composites (PCCs), it is still a challenge to achieve high performance PCCs with excellent thermal, mechanical, and phase change properties simultaneously. In this work, we report a spatial confining forced network assembly (SCFNA) method to efficiently prepare the thermal conductive, flexible, leak-proof hexagonal boron nitride/paraffin wax/ polydimethylsiloxane (hBN/PW/PDMS) PCCs by constructing hBN and PW thermal conductive networks as the functional matrix of PCCs. In the hBN/PW/PDMS PCCs, PW is served as the PCM, a dense hBN network provides the high thermal conductivity, and the mechanical properties and shape stability are provided by PDMS. The hBN/PW/PDMS PCCs as thermal interface materials reduce the LED chips surface temperature and exhibit efficient and reliable thermal management performance. Our work provides an efficient and economical method for the preparation of PCCs with outstanding thermal management capability. [ABSTRACT FROM AUTHOR]