Directional xylitol crystal propagation in oriented micro-channels of boron nitride aerogel for isotropic heat conduction

Self-assembly and orientation of thermally conductive fillers into ordered scaffold often lead to composites with anisotropic thermal properties. Though large thermal conductivity (TC) can be achieved in the direction of filler orientation, TC in transverse direction is greatly restricted. In this work, boron nitride (BN) scaffold was prepared by an ice-template method and then filled with xylitol crystals to form a new family of composites featuring isotropic TC. The crystallization of ice facilitates the formation of aligned BN walls in the aerogel and the subsequent filling of xylitol in the microchannels of the BN aerogel pushes the crystallization of xylitol in transverse direction. Combination of aligned crystal packs and BN walls in these composites results in high TC in both horizontal and vertical directions. TC of the composites increases with increasing BN content and the TC reaches as high as 4.53 W m⁻¹ K⁻¹ at BN loading of 18.2 wt%. These new results offer an alternative strategy to fabricate isotropic thermally conductive composites that can be used for the next generation of heat dissipating materials.