Effect of NaCl on the Lifetime of Micro- and Nanobubbles.
Micro- and nanobubbles (MNBs) are potentially useful for industrial applications such as the purification of wastewater and the promotion of physiological activities of living organisms. To develop such applications, we should understand their properties and behavior, such as their lifetime and their number density in solution. In the present study, we observed oxygen MNBs distributed in an electrolyte (NaCl) solution using a transmission electron microscope to analyze samples made with the freeze-fracture replica method. We found that MNBs in a 100 mM NaCl solution remain for at least 1 week, but at higher concentrations decay more quickly. To better understand their lifetimes, we compared measurements of the solution's dissolved oxygen concentration and the ζ-potential of the MNBs. Our detailed observations of transmission electron microscopy (TEM) images allows us to conclude that low concentrations of NaCl stabilize MNBs due to the ion shielding effect. However, higher concentrations accelerate their disappearance by reducing the repulsive force between MNBs.
Division of Applied Physics, Faculty of Engineering, Hokkaido University, N13 W8 Kita-ku, Sapporo, Hokkaido 060-8628, Japan. t-uchida@eng.hokudai.ac.jp.
Tsutomu
T
Uchida
Graduate School of Agricultural & Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan. liu@bpe.en.a.u-tokyo.ac.jp.
Shu
S
Liu
Graduate School of Agricultural & Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan. masatoshi.enari@gmail.com.
Masatoshi
M
Enari
Graduate School of Agricultural & Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan. aoshita@mail.ecc.u-tokyo.ac.jp.
Seiichi
S
Oshita
Division of Applied Physics, Faculty of Engineering, Hokkaido University, N13 W8 Kita-ku, Sapporo, Hokkaido 060-8628, Japan. k-yamazaki@eng.hokudai.ac.jp.
Kenji
K
Yamazaki
Division of Applied Physics, Faculty of Engineering, Hokkaido University, N13 W8 Kita-ku, Sapporo, Hokkaido 060-8628, Japan. gohara@eng.hokudai.ac.jp.
Kazutoshi
K
Gohara
diffusive shielding; freeze-fracture replica; ionic shielding; microbubble; nanobubble; transmission electron microscope; ζ-potential