Coalescence behavior of fully submerged CO2 nanobubbles: A molecular dynamics based parametric study

Abstract

Due to their extraordinarily extended lifetime and wide range of applications in numerous cutting-edge technologies and processes, nanobubbles have garnered a lot of attention in recent years. Nanobubble coalescence behavior is of crucial importance as it provides a clear indication of how stable these nanobubbles really are, which is vital for most nanobubble applications. The current study employs classical molecular dynamics simulation to investigate the coalescence dynamics of CO2 nanobubbles completely submerged in water. To draw a stark contrast, a comparison with air nanobubble coalescence is presented as well. It is observed that unlike air nanobubbles, CO2 nanobubbles have a tendency to hinder coalescence and do not fully coalesce into a single bubble in general. State of the entrapped gas inside the nanobubbles, electrostatic repulsion and large negative zeta-potential are the primary factors responsible for this nature. Coalescence neck growth and onset time are used to quantify the degree of partial coalescence. A compilation of findings and analysis for a total of 8 factors and 40 cases has been provided, demonstrating how CO2 nanobubble coalescence is influenced by many factors such as nanobubble size, surrounding pressure, temperature, the presence of air, and more. These parametric studies show that the degree of coalescence is tunable through adjustment of certain parameters. The parametric exploration of CO2 nanobubble coalescence behavior might serve as control strategies in various nanobubble driven processes.