Preparation and thermophysical study on a super stable copper oxide/deep eutectic solvent nanofluid.

• Super stable copper oxide/DES nanofluids were achieved. • One-step preparation protocol from homogeneous DES Cu(OH) 2 solution was realized; • Thermophysic and photothermal characteristics of the nanofluids were comprehensively studied. Nanofluid has gained vast attention as a novel heat transfer working fluid owing to its superiority in thermal conductivity and rheological properties. Meanwhile, the liquid range and the stability of nanofluids are of great significance since it dominates the utilization scope of a working fluid. In this work, with the aim at solving the poor stability associated with short liquid range of traditional nanofluids, a novel "one-step" preparation protocol was developed using Cu(OH) 2 as a precursor and deep eutectic solvents (DESs) as dispersing medium. The as-prepared nanofluid bears an extraordinary static stability that can be kept for at least two months without observation of any sedimentation thanks to the in-situ formed Cu 2 O nanoparticle in DESs under a microwave irradiation condition and wide liquid range attributed to the low saturated pressure of DESs. Structural analysis, such as SEM, TEM, XRD, XPS and FTIR analysis, and thermophysical properties of the nanofluids were subject to a comprehensive study. Thermal conductivity analysis indicated that the presence of Cu 2 O nanoparticle slightly impacts the thermal conductivity when the mass fraction of the nanoparticle is small. Notably, this DESs based nanofluid features promising photothermal conversion that can reach 83.74% with the addition of 0.1 wt % Cu 2 O nanoparticle. This study provides an important avenue for the preparation of nanofluids with high static stability. [ABSTRACT FROM AUTHOR]