Multiple crosslinking-Stretch-induced multi-level orientation structure BNNS/Ca-SA/D films with high thermal conductive performance

Polymer-based thermally conductive composites have garnered significant attention in recent years due to their critical applications in areas of national strategic importance. Nevertheless, the inherently limited thermal conductivity and mechanical properties of polymers pose challenges to their practical application. Recent research indicates that employing exogenous methods and facilitating molecular-level interactions between fillers and cross-linkers are effective strategies to overcome these limitations. In this study, with the aid of the ionic effect during the sol-gel phase transition of aqueous sodium alginate molecules in the presence of divalent cations and biaxial stretching, combined with the hydrogen bonding between boron nitride nanosheets (BNNS) with excellent thermal conductivity and sodium alginate (SA) molecules, the BNNS-calcium alginate (BNNS/Ca-SA/D) films were constructed by the strategy of gel reconstruction, rehydration, evaporation-assisted self-assembly and biaxial stretching. By designing anisotropic structures with closely aligned interconnected BNNS (Herman orientation parameter as high as 0.865), the BNNS/Ca-SA/D films with a BNNS loading of 40 wt% were characterized by high in-plane thermal conductivity (45.50 W•m⁻¹•K⁻¹) and good mechanical properties. Combined with finite element analysis to simulate the heat transfer process, the “thermo-mechanical” coupled multilevel oriented structure composite films were constructed due to the densification arrangement and the increase of interfacial adhesion during multiple cross-linking processes, and the orientation arrangement of BNNS during the tensile-induced process. The potential of the BNNS/Ca-SA/D films developed in this study for thermal management applications has been demonstrated by the practical application of thermal management devices and the human body. The polymer-based thermally conductive films developed in this paper offer promising applications for thermal management systems in modern power electronics.