Sandwich structured RGO/CNF/RGO composite films for superior mechanical and thermally conductive properties

It is urgent and significant to develop a thermal interface material (TIM) with both high thermal conductivity and excellent mechanical strength for high-performance electronic devices. For the first time, we designed and fabricated a sandwich structured TIM, constructed by a cellulose nanofiber (CNF) core layer sandwiched by reduced graphene oxide (rGO) shell, with copper ions as a crosslinker, via a facile and scalable vacuum filtration process. The continuous rGO layers on the surface of the composite provided a good thermal conductive pathway for the composite films. The thermal conductivity of the sandwiched films with 8.0 wt% rGO reached 29.5 W/mK, which is over eight times than the CNF films, and realized an ultrafast thermal diffusion time at 73 ms. The sandwich structure combined with the cross-linker of copper ions also plays a synergistic role in construct mechanical strength. Compared to the CNF, the tensile strength of the sandwiched films with 8.0 wt% rGO unprecedentedly reached 314 MPa (nearly three times of bare CNF films), and the elongation increased 63%. In addition, the films also shows high water stability and excellent flexibility, which makes it a very promising for advanced flexible or wearable electronics. This work provides a new insight in rational structure design and novel scalable fabrication strategy to develop TIM with outstanding mechanical strength and thermal conductivity.