Understanding the merging dynamics of surface nanobubbles and the resulting capillary force between particles from molecular simulations

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Nanobubbles are gas-filled cavities in liquids with diameters ranging from tens to hundreds of nanometers. The key difference between nanobubbles and ordinary, larger bubbles is that larger bubbles rise rapidly to the surface of a liquid and burst, while nanobubbles can remain suspended in liquids for hours or even days. Due to their unique properties, nanobubbles are extremely useful in a broad range of technological applications such as froth flotation, wastewater treatment, detergent-free cleaning, and de-inking. The key process in these applications is the coalescence of nanobubbles on the surfaces of particles, which results in the formation of particle aggregates in a liquid. The main objective of this project is to use numerical simulations and theoretical models to understand the merging dynamics of nanobubbles and the resulting capillary force between adjoining particles. The education activities related to this project will attract high school students, especially those in underrepresented groups, in the central valley (California) to the engineering program, train students to conduct research in bubble dynamics, and guide students toward doctoral research programs in STEM.This project will use molecular dynamics simulations coupled with continuum-based theoretical analysis to study the effects of bubble size, surface tension, contact angle, and surface topology on merging dynamics of nanobubbles and the resulting capillary force between particles coated with nanobubbles. The molecular level modeling will enable the study of microscopic details that are inaccessible to experiments and will provide a fundamental understanding and quantitative predictions of many key aspects of nanobubble dynamics and the nanobubble capillary force between particles. Moreover, such microscopic predictions are not hindered by many assumptions and approximations used in continuum and theoretical modeling. The modeling results will enable practitioners to develop strategies for enhancing the flotation rate of fine/ultrafine mineral particles and to improve removal rates of contaminants in processes such as wastewater treatment, surface cleaning, and recycling of paper.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.