We assume that 60% of the TC is regarded as consisting of surfactant, 𝑁 = 𝑁 × 60% ≈ 3 × 10 . It is clear that 𝑁 ≈ 𝑁 , meaning that even for the ultrapure water used in experiments, it still contains the sufficient amount of contaminants that is able to stabilize the bulk nanobubbles with a typical concentration of 𝑐 ≈ 10 /𝑚𝐿 reported experimentally.