Journal
LANGMUIR
Volume -, Issue -, Pages -Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.langmuir.2c02042
Keywords
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Funding
- National Science and Technology Council R.O.C.
- [110-2221-M-001-067-MY3]
- [110-2221-E-012-002]
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The study investigates the properties and stability mechanism of gas clusters in water using molecular dynamics simulations. The findings reveal power law relationships between cluster morphological deformation and vibrational frequency, indicating that the surface energy dissipates through morphological changes. Increasing pressure in the liquid region alters the water molecular network at the interface. The overall gas concentration is oversaturated, but the interfacial effects reduce the gas pressure and demand for oversaturation. The electrostatic stress is greater than the gas pressure inside the cluster, but the induced tension is much lower than the interfacial tension. The potential of mean force profiles show a barrier potential at the interface hinders gas particles from escaping the cluster.
The Young-Laplace equation suggests that nanosized gas clusters would dissolve under the effects of perturbation. The fact that nanobubbles are observed raises questions as to the mechanism underlying their stability. In the current study, we used all-atom molecular dynamics simulations to investigate the gas-water interfacial properties of gas clusters. We employed the instantaneous coarse-graining method to define the fluctuating boundaries and analyze the deformation of gas clusters. Fourier transform analysis of the cluster morphology revealed that the radius and morphology deformation variations exhibit power law relationships with the vibrational frequency, indicating that the surface energy dissipated through morphology variations. Increasing pressure in the liquid region was found to alter the network of water molecules at the interface, whereas increasing pressure in the gas region did not exhibit this effect. The overall gas concentration was oversaturated and proportional to the gas density inside the clusters. However, the result of comparison with Henry's law reveals that the gas pressure at the interface reduced by the interfacial effects is much lower than that inside the gas region, thus reducing the demanding degree of oversaturation. Originating from the interfacial charge allocation, the magnitude of the electrostatic stress is greater than that of the gas pressure inside the cluster. However, the magnitude of the reversed tension induced by electrostatic stress is far below the value of interfacial tension. The potential of mean force (PMF) profiles revealed that a barrier potential at the interface hindered gas particles from escaping the cluster. Several effects contribute to stabilizing the gas clusters in water, including high-frequency morphological deformation, electrostatic stress, reduced interfacial tension, and gas oversaturation conditions. Our results suggest that gas clusters can exist in water under gas oversaturation conditions in the absence of hydrophobic contaminants or pinning charges at interfaces.
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