A Molecular Dynamics Study of the Stabilization of Nanobubbles by Surfactants

Abstract

A molecular dynamics simulation of an aqueous surfactant system : water liquid and alcohols below the liquid saturation density is carried out to investigate the stability of "nanobubbles" and the structure of the gas-liquid interface. To analyze the effect of the surfactant structure, volume, and polarization on the stability of bubble nuclei, we use TIP3P water as the solvent molecules and 1-propanol, 1-pentanol, 1-heptanol as the surfactant molecules. The intramolecular energy and motion of all molecules is taken into account, by applying the AMBER force field. Adding polarized surfactants to the metastable state of liquid in which bubble nuclei cannot exist stably, it is found that a stable bubble is formed and hydroxyl groups of surfactants tend to point to the liquid phase at the gas-liquid interface. It is also shown that the longer hydrophobic chains the surfactants have, the more stably the bubble nuclei can exist.