Evaluating the colloidal stability of graphene oxide nanosheet in heat transfer fluids

Adding small amount of graphene oxide (GO) into heat transfer fluids has been found to enhance thermophysical properties of the fluids. Nevertheless, the efficiency a GO-based nanofluid for heat transfer application is depending on ability of the GO to stay disperse in the base fluid. Realizing this, the present study investigated the long-term colloidal stability (up to 2 days) of GO upon added into different types of commonly used heat transfer fluids. Results showed that GO can be dispersed in distilled water, ethylene glycol, propylene glycol, and ethanol upon subjected to sonication. However, rapid agglomeration and sedimentation of the GO in ethanol medium rendering it a less effective heat transfer nanofluid. On the other hand, GO nanoparticles were observed to be highly stable in both ethylene glycol and propylene glycol, possibly due to protic nature of these two base fluids. In fact, the GO nanoparticles were found to be ~100 % and > 82 % stable in ethylene glycol and propylene glycol-rich medium, respectively; a condition much better than the one dispersed in distilled water medium. Interestingly, it was found that the GO failed to disperse in engine oil which made up of non-polar hydrocarbon chain, hence, suggested its poor compatibility with this type of heat transfer fluid. It is envisaged that outcome from the present work can provide a proper guideline on the selection of suitable fluid for making GO-based heat transfer fluid.