Preparation and thermo-physical properties of stable graphene/water nanofluids for thermal management

Stability issue is a core factor to appraise the performance of nanofluids since it heavily associates with its practical utilization scope in a range of occasions. To improve the static stability of graphene filled nanofluids, in this work, a quaternary ammonium species containing polymer wrapped graphene (PWG) was synthesized via an in-situ polymerization protocol. Stability study reveals that this quaternary ammonium group plays an important role in adjusting the compatibility between graphene and base solvent owing to its amphiphilic characteristic. The as-prepared nanofluids exhibit an outstanding stability that it can be kept uneventfully in a term longer than 200 days. Further study shows that these nanofluids not only afford an enhancement in static thermal conductivity enhancement, but also, more importantly, give an almost doubled convective heat transfer coefficient in a flow condition by filling only 0.4 wt% of PWG which opens an important avenue for the application graphene filled nanofluids.