Research ArticleMATERIALS SCIENCE

Massive generation of metastable bulk nanobubbles in water by external electric fields

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Science Advances  03 Apr 2020:
Vol. 6, no. 14, eaaz0094
DOI: 10.1126/sciadv.aaz0094
  • Fig. 1 Schematic of pressure vessel rig.

    (A) The four main sections are gas supplier, distribution terminal, the pressure cell itself, and temperature regulation jacket. High-purity (N5-level) gases (methane and O2) are supplied to the 0.34-liter, 200-bar–rated stainless steel and rocker-mounted vessel through the distribution terminal, with line cleaning before purging the desired gas, by way of a mass flow controller and accurate measurement of gas loading into the deionized water-loaded vessel. The system operates under constant volume modes, with the inlet valve closed upon reaching the desired pressure (~90 bar), and pressure logged digitally every second for the experiment’s duration. A temperature control system operates in a jacket around the vessel (held at 20°C). A 60-V DC electric current supply was introduced via sheath-covered wires (preventing direct wire-water contact) into a three-dimensional–printed plastic (B), horizontally mounted holder immersed in water (cf. fig. S2, with discussion on the resultant electric field distribution inside the pressure cell). (Photo credit: Mohammad Reza Ghaani.)

  • Fig. 2 Gas uptake as a function of time.

    Results shown for oxygen (A) and methane (B) at 60 V (with average field intensity of 12 kV/m), expressed as a multiple of their respective HLCs (right axis) and in g/liter (left axis) at prevailing background pressures of ~90 bar; plateaux occurred within less than 3 hours.

  • Fig. 3 NB formation and ensuing stability enhancement via applied static electric fields in NEMD.

    (A) Starting with individually solvated propane molecules in water (top), field application leads to NB formation: The bottom panel shows NBs within 3 ns in a field (1.5 V/nm). (B) Evolution of the accessible bubble surface area to water molecules; increasing NB stability is evident—1.5 V/nm readily promotes NB formation, with a higher surface area, stable for more than 10 ns.

  • Fig. 4 NB detection via dynamic light scattering (Malvern Zetasizer Pro); this uses fluctuations in laser light scattering traveling through the sample solution.

    The measurements are all done after 12 to 24 hours after depressurizing and field removal. The measurement repeated three times on three samples for better accuracy. A control sample was also measured with the same experimental process except in the absence of field.

  • Fig. 5 NB evolution under ambient, STP conditions after field removal.

    (A) Dual-regime mass loss during the first 50 hours upon field removal and storage under ambient temperature/pressure conditions. (B) Evolution in methane-bubble Sauter mean diameter over a 4-month period (three replicas for each measurement); very slow bubble growth is seen.

Supplementary Materials

  • Supplementary Materials

    Massive generation of metastable bulk nanobubbles in water by external electric fields

    Mohammad Reza Ghaani, Peter G. Kusalik, Niall J. English

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    This PDF file includes:

    • Sections S1 to S5
    • Figs. S1 to S7
    • Tables S1 to S3
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