Surface tension of supercooled graphene oxide nanofluids measured with acoustic levitation

The surface tensions of graphene oxide nanofluids of five mass concentrations were measured by the oscillation droplet method in an acoustic levitator. The oscillation information of the suspension droplets was obtained by combining acoustic levitation with image recognition technology, and a shape correction coefficient a was introduced to modify the Rayleigh equation. Over the temperature ranging from − 7 to 10 °C, the surface tension of the graphene oxide nanofluids increases with increasing mass concentration and decreases with increasing temperature. Compared with the surface tension changes caused by an increase in the mass concentrations of nanofluids from 0.08 to 0.12% at − 7 °C, the surface tension slowly increases from 79.144 to 80.664 mN m−1 when the mass concentration increases from 0.02 to 0.08%. The change rate of the surface tension with temperature is linear in both supercooled and non-supercooled states. For nanofluids with a mass concentration of 0.02%, the values are − 0.185 and − 0.186, respectively, which are basically the same. However, with an increase in mass concentration, the surface tension increases abnormally in supercooled state. For nanofluids with mass concentrations of 0.05% and 0.08%, the curve of the surface tension has an inflection point at − 1.0 °C, while for mass concentrations of 0.10% and 0.12%, the inflection point is at 1.0 °C. All inflection points are distributed around the triple point temperature of water.