Standards and Guidelines

There are no universal standards exclusively dedicated to nanobubbles yet, but various organizations are working on guidelines:

  • ISO/TC 281 (Fine Bubble Technology):
    • The International Organization for Standardization (ISO) has established a technical committee (TC 281) for fine bubble technology, which includes the classification, measurement, and applications of nanobubbles.
  • ASTM International:
    • Working on methods and protocols for characterizing nanobubbles.

Detecting Nanobubbles

Nanobubbles are challenging to detect due to their small size, but advanced techniques have been developed:

  1. Dynamic Light Scattering (DLS):

    • Description: Measures the size distribution of nanobubbles based on the scattering of light caused by their Brownian motion.
    • Best For: Determining the size and stability of nanobubbles in solution.

  2. Nanoparticle Tracking Analysis (NTA):

    • Description: Tracks the movement of individual nanobubbles under a microscope to determine their size and concentration.
    • Best For: High-resolution measurement of particle size and number concentration.

  3. Zeta Potential Measurement:

    • Description: Measures the surface charge (zeta potential) of nanobubbles, which is critical for their stability.
    • Best For: Confirming the presence of stable nanobubbles.

  4. Optical Microscopy (Specialized Techniques):

    • Description: Advanced microscopy techniques (e.g., Total Internal Reflection Fluorescence Microscopy) can detect nanobubbles under specific conditions.
    • Best For: Visualizing nanobubbles on surfaces or interfaces.

  5. Cryo-Transmission Electron Microscopy (Cryo-TEM):

    • Description: Uses electron microscopy to visualize frozen nanobubbles at extremely high resolution.
    • Best For: Detailed structural analysis of nanobubbles.

  6. Ultrasound Attenuation and Scattering:

    • Description: Measures the interaction of ultrasound waves with nanobubbles, providing information about their presence and size.
    • Best For: Detecting nanobubbles in bulk water.

  7. Resistivity or Conductivity Changes:

    • Description: Nanobubbles can alter the electrical properties of water, which can be measured using conductivity sensors.
    • Best For: Indirect detection of nanobubbles in certain applications

Classification of Nanobubbles

They are classified as bubbles smaller than 200 nm with unique properties like stability, high gas transfer efficiency, and a negatively charged surface.

Detection methods include DLS, NTA, zeta potential measurement, cryo-TEM, and ultrasound techniques. ISO and ASTM are actively developing standards to standardize the field of nanobubbles.

  1. Size:

    • Nanobubbles are generally classified as having a diameter of less than 200 nanometers (nm), with most being around 100 nm or smaller.
    • They are significantly smaller than microbubbles (1–100 micrometers) and have unique physical properties.

  2. Properties:

    • High Surface Area: Despite their small size, they provide a large surface area for gas transfer.
    • Long Stability: Unlike larger bubbles, nanobubbles can remain stable in water for days to weeks due to their near-zero buoyancy and high internal pressure.
    • Negative Surface Charge: Nanobubbles often have a negatively charged surface (zeta potential), which contributes to their stability and interaction with particles.
    • High Gas Transfer Efficiency: Due to their small size and surface properties, they dissolve gases efficiently into liquids.