# Micro-Nanobubble Technology in Surface Cleaning and Defouling
## 2 Properties and Mechanisms of MNs
### NBs: Characteristics, Applications, and Radical Generation  
The presence and exceptional stability of BNBs in aqueous solutions was demonstrated by [PERSON] et al. [42] (Figure 5). According to conventional belief, under typical circumstances, NBs should dissolve quickly because of their small size and high internal pressure. However, the experimental findings in this study showed that BNBs might endure long periods without significant dissolution. The results showed that the surrounding liquid environment, zeta potential, and surface charge affected the stability of the NBs. To prevent coalescence and disintegration, researchers emphasized that the negatively charged interfaces of NBs produced repulsive forces. The study also examined the implications of stable NBs for a range of environmental and industrial applications. These included improved flotation procedures, increased pollutant degradation, and production of reactive radicals under particular circumstances. This study highlighted the potential of NBs as a reliable and sustainable tool for scientific improvements in materials science, environmental engineering, and medicine. It created opportunities for further investigation of the physicochemical processes that support their stability and use. Figure 4: Schematic illustration of nanobubbles (NBs) being employed in a microfluidic channel for cavitation applications. Insets show enhanced views of (**a**) NBs entering microfluidic networks that MBs are too large to reach; (**b**) the high-speed jets released during the final collapse stage, which have been proposed for the novel cavitation applications shown; and (**c**) NBs being stimulated to oscillate using high-frequency ultrasound, such as in ultrasound contrast agents. (**d**) Molecular dynamics (MD) simulation setup for our NB simulations, forced to oscillate using a vibrating piston, shown with a sliced view. The oxygen atoms are shown in red, hydrogen atoms in white, nitrogen atoms in cyan, and wall/piston atoms in gray. The inset shows an orthographic view of the three-dimensional domain, with some water molecules in the dashed box removed for clarity. Variation in (**e**) NB radius \(R\), (**f**) mean internal gas pressure \(P\), and (**g**) mean internal gas temperature \(T\), with time \(t\), for the \(\omega\) = 25 rad/ns oscillation case. Reproduced with permission from [39], CC-BY 4.0 license, Copyright © 2023 the authors. Published by the American Chemical Society. [PERSON] et al. [43] described a process for creating nanoparticles with mean diameters of 90, 260, and 650 nm with a single hemispherical depression (nanocups), which may be adjusted to trap an NB. The inertial cavitation threshold as a function of the cavity size and frequency was predicted using a modified Rayleigh-Plesset crevice model, and these predictions were confirmed experimentally. This study demonstrated that nanocups can stabilize gases on their surfaces by adjusting the width of the nanocavities. This significantly reduced the inertial cavitation threshold of pure water exposed to ultrasound from over 30 MPa to as low as 1 MPa. At two frequencies, the nanocrevice model predicted the inertial cavitation thresholds of cavity-size-tuned nanocups, which were consistent with experimental findings. Nanocups generated only broadband signals in response to ultrasonic exposure, suggesting that only inertial cavitation was nucleated. Compared with the 2 min previously reported for MBs, these sonic emissions were maintained for at least 10 min without the nuclei being replenished. Applications such as cancer therapy and sonochemistry, in which both particle size and cavitation sustainability are critical because of tumor morphology constraints and the safe range of frequencies and acoustic pressure amplitudes used, greatly benefit from the ability to tune the size and inertial cavitation threshold of nanocups. This allows for the creation of application-specific cavitation nuclei. [PERSON] et al.