Effect of inorganic cations on bubble-oil droplet coalescence in aqueous solution

Understanding the interaction between bubbles and surfactant-stabilized oil droplets in electrolyte solutions is essential for controlling film stability and enhancing flotation efficiency. Compared to well-studied bubble coalescence, bubble-droplet interactions involve distinct interfacial dynamics due to the presence of surface-active agents. This study combined molecular dynamics simulations with macroscopic coalescence experiments to investigate the effects of metal ion hydration and reagent adsorption on bubble-droplet coalescence, aiming to elucidate the coupling between interfacial dynamics and internal bubble pressure under ionic conditions. Studies show that multivalent ions disrupt the hydrogen-bonding network of water, promoting 2-octanol adsorption at the gas-liquid interface and altering liquid film surface tension. The resulting surface tension gradients, combined with fluid viscosity, govern interfacial and dynamic pressures within the film, ultimately dictating internal bubble pressure changes during coalescence. The findings provide molecular-level insights into the regulation of surfactant behavior at gas-liquid interfaces by metal ions, offering a theoretical basis for the control of froth flotation performance.