Tailoring water freezing kinetics with nanobubbles: A gas-dependent modulatory effect on water solidification

This study hypothesised that nanobubbles (NBs) can significantly influence the time required for water to undergo a complete liquid-to-solid phase transition (solidification). We further posited that this effect is dependent on the gas species used to generate the NBs, driven by their unique interfacial electrical properties and impact on ice nucleation and the water liquid-solid interface in water solidification.

Laboratory experiments were conducted to investigate the effect of air NBs and CO₂ NBs on water solidification time. The experiments measured the time to complete water solidification at ambient temperatures of -10 °C and - 20 °C. Concurrently, numerical simulations of transient heat conduction were performed to assess the apparent energy released during the phase transition in the presence of NBs, providing a comparative measure for the observed solidification time changes.

The experimental results revealed that NBs do indeed alter the completion time of water solidification. Specifically, air NBs delayed solidification by up to 8.7 ± 1.9 %, while CO₂ NBs accelerated it by up to 11.4 ± 2.5 % at an ambient temperature of -20 °C. This alteration can be explained by numerous OH^- ions and the Hofmeister-like behaviour of CO₃^2-. The numerical simulations corroborated these findings, showing that the observed changes in solidification time are comparable to an increase of +8 ± 2 % in the overall apparent energy released for air NBs and a decrease of -10 ± 2 % for CO₂ NBs. These findings suggest that NBs, depending on the gas species, offer a promising "green" nanomaterial for controlling water freezing and anti-freezing processes.