Microchannels-enabled vertical alignment of hexagonal boron nitride in silicone rubber composites to achieve high through-plane thermal conductivity

Hexagonal boron nitride (h-BN) with high vertical alignment in polymer composites is necessary to improve through-plane thermal conductivity (TC) for thermal management applications. However, how to achieve simple, efficient and precise control of h-BN vertical alignment in polymer composites remains a challenge. Herein, a novel concept of inducing vertical alignment of h-BN in silicone rubber (SR) composites via controlling flow patterns in specially designed microchannels was proposed. The extremely strong elongational and shear stresses provided by the narrow section of the microchannels induced h-BN to align perpendicular to the flow direction. In the subsequent channel, the weak shear stress manipulated h-BN to form a ladder structure in the SR composites, including the vertical core layer and horizontal skin layer. Such ladder structure not only improved the through-plane TC of SR composite but also prevented overheating in the face of local heat sources. Moreover, the obtained SR composites exhibit a through-plane TC of 5.08 W/mK at 34.3 vol % h-BN loading when the horizontal skin layer was removed, indicating excellent heat transfer efficiency for thermal management application. We believe that this work would strengthen both scientific and technological cognition of the filler alignment during polymer composites processing.