Tree-ring structured phase change materials with high through-plane thermal conductivity and flexibility for advanced thermal management

Phase change materials (PCMs) as one of the most promising latent heat storage materials have been applied for thermal management of electronic devices. Nonetheless, simultaneously endowing PCMs with high through-plane thermal conductivity and flexibility remains challenging. Herein, a coupling strategy combining scraping, hot compression, and roll-cutting is proposed to fabricate polydimethylsiloxane/paraffin/boron nitride (PDMS/PW/BN) composites. The BN alignment across the in-plane (x-y direction) was firstly obtained via scraping, then hot compression and roll-cutting were introduced to induce BN aligned across the through-plane (z-direction). Consequently, PW was wrapped by the cross-linked PDMS/BN network, thus forming a similar tree-ring structure to natural wood. The tree-ring structure effectively avoided the liquid leakage of PW, thus showing a high dimension retention ratio of 98 %. The vertical orientation of the BN network imparted the PCMs improved through-plane thermal conductivity of the PCMs to 2.16 W·m−1·K−1 at a BN loading of 13.0 wt%, showing a remarkable improvement of 943 % in comparison with PDMS/PW. Interestingly, the PCMs exhibited tunable thermal conductivity by triggering the melting-crystallization transition of PW. The in-situ X-ray diffraction indicated that the BN network rearrangement occurred during the phase transition. Furthermore, the good thermal management capability of PCMs was practically confirmed on working chips and via finite element simulation. This work presents a cost-effective approach for producing flexible PCMs with high through-plane thermal conductivity, which have the potential to be used in the thermal management of advanced electronics.