A Classical Thermodynamic\nModel for Dispersed Nanophase\nStability and Its Application for Investigating the Stability of Air\nNanobubbles in Water

There is a growing need to understand\nthe theoretical\nbasis of\nnanophase stability to enable the control and manipulation of their\nproperties. Bulk nanobubbles are examples of dispersed nanophases\nthat show promising properties for clean, green, sustainable, and\nyield enhancement applications. In this work, a chemical equilibrium\nthermodynamic framework is presented to study the nanophase. This\nframework is used to prove the spontaneity of nanobubble formation\nand thereby its stability through the estimation of the corresponding\nGibbs energy. Estimation of bubble pressure, temperature, and internal\ngas composition is also carried out for a typical air–water\nnanobubble system by employing this framework. The work shows that\nthe curved nanointerface is critical for nanobubble stability and\nalso exhibits unusual characteristics as it traps gas molecules at\nextremely high pressures, ∼1100 atm, when the bulk pressure\nis just 1 atm, while maintaining high surface area and reactivity.\nWe were able to thermodynamically and mathematically show the existence\nof very strong interactions at the nanobubble interface, the nature\nof which is assumed to be primarily Coulombic, but how the Coulombic\nforces form extremely strong molecular traps is still unknown. The\nexistence of these interfacial interactions, i.e., their origin and\nnature, have to be explored experimentally. However, there are no\nprobes that can measure the charge present on the Stern layer around\na nanobubble as well as pressure, temperature, and composition inside\na nanobubble dispersed in a bulk fluid. Thus, the development of new\ncharacterization techniques or an investigation using molecular simulation\nin the future could validate the estimates of nanobubble pressure,\ntemperature, and composition, as well as the interfacial interactions\nestimated in this work.