The second situation is for the multi-component amphiphile monolayer (Fig. ), in which the mixing of long-chain-surfactant and short-chain-surfactant (e.g., alcohol) lowers substantially the bending constant κ. We believe that the trace organic contaminant-stabilized bulk nanobubbles belongs to this situation. When κ is small enough (~𝑘 𝑇), the thermal motion becomes one of dominating factor determining bubble size. The competition between thermal and bending energy can be described by the notion of persistence length 𝜉 , which plays an essential role in determining the nanobubble size, as for the microemulsions. For isotropic film of microemulsions, de Gennes and Taupin proposed that the droplet size will be determined by the persistence length 𝜉 of the interface: at scales smaller than 𝜉 the interface is essentially close to flat, whereas at scales larger than 𝜉 it is strongly wrinkled. Similarly, for spherical nanobubble we can assume that 𝜉 is related to the rigidity κ by