Understanding CO ₂ nanobubbles’ behaviour and (meta)stability in water under different electric field strengths: non-equilibrium molecular-dynamics simulation

Nano-bubbles and -droplets are somewhat of an enigma with respect to their poorly-understood microscopic behaviour, including interactions with their surrounding solvent milieu – not least of which is their growth and (meta)stability. Following a recent increase in our understanding of the role of electric fields in influencing these microscopic processes, the present study scrutinises the growth/stability of CO2 nanobubbles under varying electric field strengths, by means of non-equilibrium molecular-dynamics simulations. Inter alia, the number and size of gas clusters per frame, the hydrogen bonds, the water dipole orientation and the cluster density were tracked. Our results showed that nucleation and growth occurred rapidly in the simulations, with a gradual increase in the number of clusters and a general reduction in nanobubble size with increasing values of the electric field strength (up to 0.5 V/nm). We found that higher field strengths inhibited nanobubble growth by softening the H-bond network formed by water molecules at the interface, as a result of the overall polarisation of water dipoles along the direction of the electric field.