# Micro-Nanobubble Technology in Surface Cleaning and Defouling
## 2 Properties and Mechanisms of MNs
### Role in Cavitation and Emulsion Formation  
Considering that they provide special mechanisms for energy transfer, interface stabilization, and radical production, NBs are essential for cavitation dynamics and emulsion formation [6]. Owing to these qualities, they are extremely important in various applications, including advanced wastewater treatment, microfluidic cleaning, and the food and cosmetics sectors. The potential of NBs for novel solutions, such as self-emulsifying systems and improved cleaning technologies, is highlighted by their capacity to reduce interfacial energy and affect emulsification processes [7]. The behavior of NBs during cavitation and emulsion stabilization has been better understood because of recent theoretical and experimental research, which has produced new frameworks and techniques for maximizing their industrial and environmental uses. [PERSON] et al. [37] theoretically investigated a Pickering-like emulsion stabilized by tiny bubbles, in which the attachment of bubbles to an oil-water interface resulted in a decrease  
Figure 3: A schematic view of the experimental processes of different solutions prior to particle-bubble attachment tests. Reproduced with permission from [35], Creative Commons CC-BY, Copyright © 2022 the author(s). Published by Elsevier B.V.  
in the interfacial energy. Self-emulsification, in which the energy required to create a new water-oil contact is exceeded, can result from this energy reduction. A phase diagram was constructed to illustrate the quantitatively defined requirements for self-emulsification. Despite being temporary, the Pickering-like emulsion improved the cleansing qualities of NBs, which made it useful for eliminating oil from skin and clothing. According to the study, this phenomenon may stimulate more experimental research on the relationship between fine bubbles and emulsions. [PERSON] et al. [38] investigated a promising and sustainable method for the remediation of oil-contaminated sand using self-collapsing MBs. The study discovered that the main variables influencing oil removal were the size of the sand grains, the kinematic viscosity of the oil, and the interaction between the oil and sand surfaces. In controlling the separation of oil from the sand, the contact between the surfaces of the oil and the sand was more important than the kinematic viscosity. Kinematic viscosity affected the system's ability to remove oil after it was removed. When MBs and mechanical stirring were combined, the remediation time was even shorter than when MBs were used alone. Furthermore, employing MBs with diameters less than 50 \(\upmu\)m demonstrated significant promise for creating a sustainable, chemical-free method of cleaning up oil spills. [PERSON] et al. [39] created a new theoretical framework to explain the behavior of NB cavitation better, particularly in relation to microfluidic cleaning, cancer treatment, and improved wastewater treatment (Figure 4). The model used the van der Waals equation of state and incorporated a temperature jump at the liquid-gas interface to account for nonequilibrium processes and the nonideal nature of the NBs' internal gas phase. The results demonstrated that a thermal response analysis utilizing the polytropic process frequently leads to an incorrect interpretation of NB oscillations as adiabatic. In practice, the oscillations resemble iso-thermal behavior, and the model predictions match molecular dynamics simulations quite well. [PERSON] et al. [40] presented a new electro-Fenton method that combined a sacrificial iron anode with NB aeration. While the sacrificial iron anode gradually increased the concentrations of Fe\({}^{2+}\) and total iron ions, NB aeration dramatically improved the oxygen transfer efficiency (DO 10.55 mg/L). Hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) was produced in situ and reached a concentration of 310 mg/L owing to the combined action of NB aeration and the sacrificial iron anode.