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Solvent exchange; Surface nanobubbles; Growth dynamics; Hydrophobic cavity arrays
Abstract:
Solvent exchange is a flow process to induce a transient oversaturation for forming nanobubbles or nanodroplets on solid surfaces by displacing the solution of gases or droplet liquids with a controlled flow of a poor solvent. In this work, we experimentally and numerically investigate the effect of the flow rate and other control parameters on the formation of microbubbles on hydrophobic cavity arrays during the solvent exchange process. We find that the growth rate, location, and number density of microbubbles are closely related to flow rate, solvent concentration, cavity distance, and spatial arrangement. Higher growth rates and number densities of the bubbles were obtained for faster solvent exchange flow rates. The competition of neighbouring growing bubbles for dissolved gas is greatly alleviated when the inter-cavity distance is increased from 13 μm to 40 μm. The effects of the flow rate and the cavity spacing on the bubble growth are in agreement with the observations from our three-dimensional numerical simulations. The findings reported in this work provide important insight into the formation of multiple interacting surface microbubbles under various flow conditions. The understanding may be extended to a smaller scale for the growth of surface nanobubbles during solvent exchange, which is much harder to visualize in experiments.
