Dual plasma synthesis and characterization of a stable copper–ethylene glycol nanofluid

This article addresses the issue of metallic nanoparticle suspension (nanofluid) stabilization without the use of traditional surface-stabilizing agents such as surfactants. A dual plasma process for the single-step synthesis of a copper–ethylene glycol nanofluid is presented. The process uses a combination of low-pressure pulsed cathodic arc erosion to generate metal nanoparticles and in-flight radio-frequency glow discharge plasma functionalization for surface stabilization. The surface-stabilized nanoparticles are collected in situ by a falling film of ethylene glycol, the vapours of which are used for plasma functionalization. Little to no agglomeration is observed in the suspension, although this process is shown to occur when the produced suspensions are heated to temperatures well beyond the range of effectiveness of typical surfactants. This thermally induced agglomeration is demonstrated to be fully reversible. The stability of the suspension is confirmed by UV–Vis absorption spectrometry and electron microscopy. The particles synthesized are also shown to be re-dispersible in aqueous media. Though no heat transfer enhancement was observed due to the low nanoparticle loading, this study demonstrates for the first time that high temperature-stable nanofluids containing metal nanoparticles can be synthesized in a single-step, without manipulation outside the controlled synthesis environment and without the post-addition of surfactants.