Optically transparent, thermally conductive film made of hexagonal boron nitride nanosheets via vacuum filtration assisted transfer printing

Abstract

In this thesis, fabrication of highly thermally conductive and optically transparent films using hexagonal boron nitride(h-BN) and transfer printing technique is demonstrated. Hexagonal boron nitride is an analogue of graphite which composed of layered structure and is optically transparent, electrically insulating, thermally conductive. To fabricate boron nitride (BN) transfer-printed film, a bulk BN particle is first exfoliated and edge-functionalized by high energy ball milling resulting in a BN nanosheets dispersion. Through vacuum filtration with PTFE membrane, BN nanosheets are stacked and anisotropically aligned through membrane surface and forming interconnected structure. Immediately after the filtration, BN nanosheet film is in a solvent swollen-state and directly transferred to substrate, deriving solvent evaporation induced interface merging. As a result, leaving BN film on substrate and selectively peel off the PTFE membrane, a defectless, smooth BN flim with uniform thickness is successfully transfer printed on various substrate including PET, Cu, glass vial, etc. The transfer-printing technique allows easy/facile thickness adjustment, surpasses optical transparency of 90%, and shows in-plane thermal conductivity over 24W/m·K. By applying the BN printing on light entrance part of LED devices, the thermal dissipation effect can be demonstrated, deriving temperature decrease over 20’C at high working voltage.