Anisotropy-Driven High Thermal Conductivity in Stretchable Poly(vinyl alcohol)/Hexagonal Boron Nitride Nanohybrid Films.

Controlling the anisotropy of two-dimensional materials with orientation-dependent heat transfer characteristics is a possible solution to resolve severe thermal issues in future electronic devices. We demonstrate a dramatic enhancement in the in-plane thermal conductivity of stretchable poly(vinyl alcohol) (PVA) nanohybrid films containing small amounts (below 10 wt %) of hexagonal boron nitride ( h-BN) nanoplatelets. The h-BN nanoplatelets were homogeneously dispersed in the PVA polymer solution by ultrasonication without additional surface modification. The mixture was used to prepare thermally conductive nanocomposite films. The in-plane thermal conductivity of the resulting PVA/ h-BN nanocomposite films increased to 6.4 W/mK when the strain was increased from 0 to 100% in the horizontal direction. More specifically, the thermal conductivity of a PVA/ h-BN composite film with 10 wt % filler loading can be improved by up to 32 times as compared to pristine PVA. This outstanding thermal conductivity value is significantly larger than that of materials currently used in in-plane thermal management systems. This result is attributed to the anisotropic alignment of h-BN particles in the PVA chain matrix during stretching, enhancing phonon conductive paths and hence improving the thermal conductivity and thermal properties of PVA/ h-BN nanocomposite films. These polymer nanocomposites have low cost as the amount of expensive conductive fillers is reduced and can be potentially used as high-performance materials for thermal management systems such as heat sink and thermal interface materials, for future electronic and electrical devices.