# Micro-Nanobubble Technology in Surface Cleaning and Defouling
## 2 Properties and Mechanisms of MNs
### NBs: Stability and Fundamental Characteristics  
NBs' exceptional stability and modes of action have made them a game-changing invention in several fields, including wastewater treatment, mineral flotation, aquaculture, agriculture, and environmental remediation [29]. Advanced instruments such as synchrotron radiation technology, which permit the accurate examination of the micro/nanostructure and electronic characteristics of materials, have greatly aided the study of these systems (Figure 2). Such knowledge is essential for understanding the exceptional stability and effectiveness of NBs in real-world applications. According to [PERSON] et al. [30], the term \"NBs\" describes gas bubbles in solutions or at solid-liquid interfaces that are at the nanoscale. Diffusion theory and the Young-Laplace equation predict that these NBs vanish in microseconds. However, a major obstacle to basic research has been the long-term stability of NBs, as demonstrated by a wealth of experimental evidence over the past 20 years. NB technology is regarded as a game-changing invention in industries such as environmental remediation, wastewater treatment, mineral flotation, agriculture, and aquaculture. Remarkable stability mechanisms and efficient action of NBs can be discovered using synchrotron radiation technology, a potent  
Figure 2: Fundamental physiochemical properties of NBs. Reproduced with permission from [29]. Copyright © 2023, Elsevier Ltd.  
instrument for investigating the micro/nanostructure and electronic structure of materials. This review examined the fundamentals of using synchrotron radiation technology in NB systems. [PERSON] et al. [31] used molecular dynamics simulations to examine the collapse dynamics of surface NBs (20-50 nm) with different contact angles (40-80\({}^{\circ}\)) and compared them with those of spherical NBs close to a solid substrate. According to their findings, surface NBs caused less damage from substrate pitting than spherical bubbles because they produced weaker jets with lower velocities, larger profiles, and less local vorticity. Surface NBs created shallower, more uniform holes whose depth was dependent on only the contact angle and not the bubble size, in contrast to spherical NBs, which formed deep, sharp-edged pits as a result of the concentrated jet impact. Additionally, this study discovered a linear link between the peak pressure impulse at the impact center and the total substrate damage, which can be utilized in computer simulations to evaluate the capability for bubble damage. According to these results, surface NB cavitation can be utilized to reduce the pitting damage in applications requiring controlled surface damage, such as precision cleaning, advanced manufacturing, and medicine. [PERSON] et al. [32] examined the effects of airflow rate and aging time on the surface tension of bulk NBs (BNBs) in water. The surface tension of the newly created NB water was substantially lower than that of pure water and progressively increased until it reached 70.5 mN/m. The size of the NBs increased as the airflow rate increased and the surface tension decreased. The surface tension was lower than that in pure water when combined with the nonionic surfactant methyl isobutyl carbonl, but it increased when combined with 2-octanol. The number and size of NBs at the gas-liquid interface, as well as their interaction with surfactant molecules, were responsible for the variations in surface tension. These factors collectively governed the surface tension of both pure water and surfactant solutions. [PERSON] et al. [33] examined the sedimentation equilibrium and Brownian motion of nanoparticles to determine their mass density during the creation of NBs. It was discovered that the particles, which had a diameter of roughly 450 nm, had a mass density of 1.06 to 1.07 g/cm\({}^{3}\), which is more than that of water and indicates that the particles were not gaseous. The findings showed that non-gaseous nanoparticles, which can sediment under gravity, were formed with the help of NBs.