Molecular and Hybrid Simulations of Nanobubble Stability

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PI: Shell, M. Scott Proposal Number: 1403259 Institution: University of California-Santa Barbara Title: Molecular and Hybrid Simulations of Nanobubble Stability This proposal addresses one of the foremost challenges in interfacial science, the critical issue of long-lived nanobubble stability on hydrophobic surfaces. A successful attack on this problem will have a significant impact on a range of emerging technologies that rely on the ability of stable nanobubbles to dramatically modify the properties of solid surfaces, including anti-fouling and surface cleaning techniques, transport in microfluidic devices, delivery of medical therapeutics, chemical processes involving biological or gas-liquid reactions, surface-induced crystallization, and catalysis. The PIs will also build on their record of involving students at multiple levels, including those from underrepresented groups (e.g., The Shell group has hosted two minority students from HBCU schools as summer research interns through UCSB's GRIP and SABRE programs), through different programs at UCSB (summer research opportunities for undergraduates and high school students, giving talks in events from minority associations and professional associations at UCSB). In particular, the PIs and graduate students will be involved with the SIMS summer program that involves top high school graduates. The main thrust of this proposal is to critically address several hypotheses for nanobubble stability, using state-of-the-art molecular and hybrid molecular continuum simulation methods that provide a complement to current experiments. The goal is to develop a thermodynamic picture of nanobubble stability because there is some evidence that the nanobubble may actually be thermodynamically stable. To that end, the PI will use molecular simulations to compute free energies of nanobubble formation as a function of bubble size, shape, composition, and solution conditions. The results will quantify the stabilities of the bubbles, and clarify whether and when they are associated with global or local (metastable) free energy minima. These free energies will also be compared with the macroscopic expectation (e.g., based on bulk surface tensions and solubilities) to assess the possible breakdown such arguments at the nanoscale. To achieve these goals, the proposal provides clearly formulated hypotheses, including both thermodynamic and dynamic transport mechanisms, that will be addressed.