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More and more micro/nanofluidic devices are proposed to improve the performance in thermal and medical applications, and nanobubbles promise a new way of controlling the heat and flow at high spatial and temporal resolutions. The long lifetime of static nanobubbles has been extensively investigated in both experiments and theoretical modeling, but the dynamic growth of nanobubbles lacks comprehensive understanding. Therefore, we conduct an experimental investigation of nanobubble growth in a graphene liquid cell, under oversaturation conditions of dissolved hydrogen gas by electron beam radiolysis of water, via in situ transmission electron microscopy (in situ liquid cell TEM). We analyze characteristic parameters of nanobubble growth, including radius, volume, extension length, nanobubble shape, contact angle, and growth rate, based on the TEM images. We demonstrate that the growth of individual nanobubbles is determined by the oversaturation level of dissolved gas and follows a diffusively controlled dynamic as described by the Epstein–Plesset model. With the information from 3D reconstruction of nanobubbles, we reveal that both growth rate and local contact angle are affected by contact line pinning. Overall, we present a comprehensive analysis of a diffusively controlled nanobubble growth subjected to dissolved hydrogen gas concentrations and contact line pinning through the growth rate, nanobubble shape, and contact angle.

Nanobubbles are typically classified as gas/vapor phase cavities in an aqueous solution with a characteristic length of approximately 100 nanometers (nm). The theoretical lifetime of these nanobubbles has been estimated to be less than ~1 microsecond at a diameter of 100 nm based upon the Young-Laplace pressure, but experimental observations have been reported that indicate that they may exist for many hours, or even days. These nanobubbles can be generated by a number of different methods, such as solvent exchange, pressure and/or temperature variations, chemical reactions, or through the electron beam radiolysis of water. The imaging methods utilized to observe these nanobubbles have evolved from low temporal resolution/high spatial resolution, using atomic force microscopy (AFM); or low spatial resolution/high temporal resolution, using optical microscopy (x-rays); or finally, high spatial/high temporal resolution using more recent electron microscopy techniques. A review of the various methods utilized in the nucleation of nanobubbles and the different imaging technologies utilized, along with a summary of the most recent experimental and theoretical investigations of the dynamic behavior and processes of these nanobubbles, including nanobubble growth, nanobubble collapse, and nanobubble coalescence, are presented, discussed and summarized.

Dynamic light scattering (DLS) along with centrifugation and shaking tests reveal that dissolved gases can significantly affect the aggregation behavior of carbon nanotubes (CNTs) dispersed in water. The CNTs in non-degassed samples form loose, stable networks having the DLS result reminiscent of semidilute polymer solutions, whereas the CNTs in degassed samples aggregate to form Brownian colloids that sediment quickly. Interestingly, the CNTs dispersed in acetone, with or without degassing, also behave like semidilute polymers in DLS experiments. We propose a surface nanobubble-assisted mechanism to explain the observed aggregation behaviors. Our work signifies that dissolved gases may play an important role in determining hydrophobicity and biomolecular functions in aqueous environments.