Evolution of Bulk Nanobubbles under Different Freezing Conditions

Abstract

The freezing process of aqueous solutions plays a crucial role in various applications including cryopreservation, glaciers, and frozen materials. However, less research has focused on the influence of nanoscale gas bubble formation or collapse in water during freezing, which may significantly impact the formation of ice crystals. Herein, we report for the first time that the freezing process can produce nanobubbles in aqueous solutions, and their size and number concentration could be changed by different cooling rates, i.e., the size would decrease as the cooling rate increased, and the maximum number concentration was found at the −80 °C system. Furthermore, increasing the dissolved gas content in the solution enhanced the production of nanobubbles, whereas for preexisting nanobubbles, the freezing resulted in a decrease in their number concentration, which was negatively correlated with the cooling rate. Our results indicated that a moderate cooling rate of −80 °C favored nanobubble generation, whereas a higher cooling rate was preferable for maintaining preexisting nanobubbles. Conversely, a lower cooling rate could be employed to eliminate preexisting nanobubbles. This study explored the evolution and stability of nanobubbles during the freezing process, providing valuable insights into the application or elimination of nanobubbles.

Effects of Nanobubbles on Photochemical Processes of Levofloxacin Photosensitizer

“…The dissolved oxygen (DO) content was measured using a DO meter with a polarographic sensor (Orion Versa Star Pro, Thermo Fisher Scientific), with each measurement repeated three times. 57 Nanoparticle Tracking Analysis Measurements. Nanoparticle tracking analysis (NTA) was used to measure the size distribution and concentration of NBs.…”

“…A detailed description of the generation of bulk NBs by the compression–decompression method is provided in the previous literature. − A brief description is as follows: the ultrapure water was degassed and placed in a metal chamber pressurized with pure N 2 to 0.6 MPa for 30 min. Then, the gas was slowly released at a flow rate of 20 standard cubic centimeters per minute (SCCM) to standard atmospheric pressure, as shown in Scheme .…”

“…Then, the gas was slowly released at a flow rate of 20 standard cubic centimeters per minute (SCCM) to standard atmospheric pressure, as shown in Scheme . The dissolved oxygen (DO) content was measured using a DO meter with a polarographic sensor (Orion Versa Star Pro, Thermo Fisher Scientific), with each measurement repeated three times …”