As nanobubble (NB) technology gains acceptance in controlled-environment agriculture (CEA), the benefits of these remarkable bubbles — particularly those less than 200 nanometers in size — have become clear. Unique properties of sub-200-nanometer NBs include low buoyancy, high mass transfer efficiency, high reactivity and exceptional stability.
These properties have proven valuable for agriculture and horticulture, as demonstrated by oxygen nanobubbles and the benefits of stable increased dissolved oxygen for crops. But the underlying mechanism behind NB stability has remained elusive. Much research has focused on the temporal changes in the size and surface charge of NBs, but few studies have explored changes in NB concentration.
To address this knowledge gap, a team of researchers led by Dr. Myoung-Hwan Park from Sahmyook University in South Korea studied the stability of high concentrations of sub-200-nanometer NBs under various conditions. Dr. Park is the Associate Professor of Chemistry and Life Science as well as the Director of the Research Center for NanoBioMaterials Lab at Sahmyook University. A peer-reviewed paper detailing their work, “Assessment of sub-200-nm nanobubbles with ultra-high stability in water,” was recently published in the journal Applied Water Science.
Nanobubble generation and tracking analysis
To study changes in NB concentrations, the researchers used a custom-made NB generator to produce air NBs in water. The generator produced more than two billion NBs per milliliter of water, each approximately 100 nanometers in size. NB stability was studied using nanoparticle tracking analysis, which involves shining a laser onto nano-scale particles suspended in a liquid and tracking their movements under a microscope. Using this accepted research technique, the researchers investigated how the number and size of NBs change under different conditions, including storage at various temperatures and exposure to physical impacts like centrifugation, shaking and stirring.
Nanobubble stability under test conditions
The team found that sub-200-nm NBs in water showed exceptional stability even after exposure to temperature variations and severe physical impacts, retaining 80–90% of their initial concentration under all the tested conditions.
Specific conditions and resulting concentrations in the NB solutions included the following:
- NBs stored for 120 days at 5 degrees Centigrade, 25C, 60C and 80C maintained 85.7%, 81.0%, 103% and 84.8% of their initial concentration, respectively.
- NBs subjected to 90 minutes of centrifugation maintained more than 90% of their initial concentration.
- NBs shaken for eight hours retained 96% of their initial concentration.
- NBs stirred for eight hours showed no appreciable change in concentrations.
In addition, no significant change in NB size was seen in any of the above tests.
The researchers concluded their findings indicate that sub-200-nm NBs exhibit remarkable stability under diverse conditions, potentially opening new avenues for bubble technologies offering a safer environment and improved efficiency in CEA, horticulture, traditional agriculture and beyond.
“NBs show significant potential for real-life applications in mass production and distribution of bubble technology in various fields, such as pharmaceuticals, cosmetics, cleaning, environment, food, agriculture and more,” says Dr. Park. “In addition, scientists are working towards reducing the reliance on harmful but indispensable chemicals, and the use of harmless gases and NBs can further support their efforts.”
Image: Sahmyook University