Study on the Formation and Properties of Trapped Nanobubbles and Surface Nanobubbles by Spontaneous and Temperature Difference Methods

Abstract

Trapped nanobubbles are gas domains trapped at nanopits on the solid-liquid interface. This is different from surface nanobubbles that usually form at the smooth surface. Herein, both trapped nanobubbles and surface nanobubbles formed on the nanopitted polystyrene film were studied by a spontaneous formation method and a temperature difference method. Trapped nanobubbles behave more flexibly than surface nanobubbles under different scanning loads. The nanopits under trapped nanobubbles appear after being subjected to large force scanning, and both trapped nanobubbles and surface nanobubbles can recover after reducing the scan load. The contact angles of the two kinds of nanobubbles were calculated and were found to be approximately constant. Configurations of trapped nanobubbles including under the pit mouth, protruding out but pinning at the pit mouth, and protruding out and extending around the pit mouth were experimentally observed. Gas oversaturation in the liquid after replacing the low-temperature water with high-temperature water was evaluated and was found to be a key factor for nanobubble formation and led to trapped nanobubbles protruding out and extending. Our study should be helpful in understanding the formation mechanism and properties of trapped nanobubbles and surface nanobubbles, and it will also be useful for further research on the control of nanobubble distribution.