Nanobubbles at the interface between hydrophobic silica and water. Image Credits: Virginia Tech
The growing significance of nanotechnology has now led to the development of nanobubbles, which is drawing a lot of attention from a variety of fields. Nanobubbles play a vital role in many sectors that include scientific research, medical and food sectors. This article will talk about the properties, applications and recent developments related to nanobubbles.
Properties of Nanobubbles
The small size of nanobubbles gives them much more interesting properties than larger bubbles, due to their high specific area and high stagnation features in the liquid phase. Free-radical generation occurs when micro- and nano-sized bubbles collapse due to the high density of ions at the gas-liquid interface that develops prior to the collapse.
It has been shown that nano-bubbles cannot remain in a stable state under atmospheric pressure due to extremely high internal pressure. Following a number of experiments, it has been suggested that the typical lifespan for a gas bubble with 100nm radius would be around 100 µs.
In saturated liquids, these nano-bubbles are extremely stable due to the absorption of ions on their surface. The gas molecules inside the nanobubbles do not come in contact with the bulk liquid, allowing the nanobubbles to last for a much longer time. Larger bubbles have air that is above atmospheric pressure, but nanobubbles contain internal pressures of tens or even hundreds of atmospheres. Under such high pressures, it has been proven that the liquid absorbs the gas inside the nanobubbles.
Applications of Nanobubbles
Some of the applications of nanobubbles which have been explored to date are listed below:
- Acceleration of metabolism in vegetables and shellfishes
- Water treatment by flotation - their high specific area makes them useful in this field
- Contrast agents for ultrasonography
- Sterilization using ozone gas
- Foam products in the food industry and other products requiring bubble stability.
- Nutritional supplement carrier in the food industry
Physicists in the Netherlands recently demonstrated the prolonged stability of nanobubbles on wet surfaces - their nanobubbles remained stable for several days. These physicists went on to compare these tiny bubbles to the bubbles found in a champagne or beer glass. They arrived at a conclusion that the longevity of these bubbles is mainly because of two significant physical properties:
- The gas molecules on the surface of the bubble leaves the surface in a perpendicular direction
- The gas molecules generally move from one side of the bubble to the other side without touching each other because of the small size of these nanobubbles. This movement allows free flow of the liquid along the bubbles and in turn pushes the gas molecules to the surface of these small bubbles, thus increasing their stability.
Physicists from the Lawrence Berkeley National Laboratory and UC Berkeley discovered that nanobubbles can be formed when graphene is stretches in a particular manner. Nanobubbles formed in this way will have electrons that behave in a very strange manner - as if they were moving in a very strong magnetic field.
Recently, the medical field has also seen major discoveries relating to nanobubbles. Researchers from the University of Texas MD Anderson Cancer Center, Rice University and Baylor College of Medicine are concentrating on the development of new techniques to directly inject genetic payloads and drugs into cancer cells.
These researchers found that this new nanobubble injection mechanism ignores the healthy cells, favouring cancer cells. They showed that the delivery of chemotherapy drugs with nanobubbles is 30 times more effective at killing cancer cells, reducing the required dosage compared to conventional treatment.
In another experiment, scientists at Rice University developed a cancer treatment technique using lasers to zap nanoparticles inside the cells, creating nanobubbles. These nanobubbles are formed when the short laser pulses strike the gold nanoparticles, and cause damage to the cancer cells. This experiment was focused on identifying and treating cancer cells in the initial stages.
All these discoveries highlight the wide spread applications of nanobubbles in various fields. Nanobubbles due to their very small size and high stability can be very useful in treating cancer, simplifying technical operations and can even act as a nutritional supplement carrier in the food industry. These applications emphasize the growing significance and demand for nanobubbles in all walks of life.
Sources and Further Reading