Figure 4.

(a) Schematics of the adsorption layer structure of a negatively charged bulk nanobubble in anionic surfactant and electrolyte solutions. The sharp air–water interface is located at $z=R$ mathematically. Surfactant molecules/ions and counterions around the surface form an adsorption layer of thickness $\delta$, and the diffuse layer starts at $z=R+\delta$. Calculated surface tension against experiment for (b) anionic surfactant (SDS) solution and (c) cationic surfactant (CTAB) solution. (d) Predicted surface charge density over a wide range of ionic surfactant concentrations.