Remarkable improvements in the stability and thermal conductivity of graphite/ethylene glycol nanofluids caused by a graphene oxide percolation structure

Abstract

Versatile efforts have been made to improve the stability of graphite/ethylene glycol (EG) nanofluids. Primitively, non-dispersible graphite nanoparticles were converted to graphite oxide nanoparticles (GONs) by acid treatment. Although GONs could be well dispersed in EG, the GONs/EG nanofluids exhibited limited stability up to less than 1 day. And then, a GO (2 wt%) percolation structure formed in EG was used to anchor and support GONs by common non-covalent interactions including hydrogen bonds, van der Waals forces and π–π conjugation. Transmission electron microscopy observations revealed that a GON–GO hybrid forms in the GON–GO (2 wt%)/EG nanofluids with evenly distributed GONs on the GO sheets, which accounted for the high stability of nanofluids up to at least 4 weeks obtained from stability tests, in sharp contrast to that of the GONs/EG nanofluids. In addition, due to the better dispersed state of GONs induced by the GO percolation structure, thermal conductivity (TC) tests demonstrated that the TC enhancements of the GON–GO (2 wt%)/EG nanofluids were also strengthened compared to that of GONs/EG nanofluids. Excitingly, the GONs–GO (2 wt%)/EG nanofluids presented here exhibited anomalous thermal conductivity enhancements up to 123% at 21 wt% GONs content and were highly stable, which might have potential applications in engineering field and energy systems.