Creation of nano-sized bubble discovers new area in cleaning and disinfactation in the food processing industries.

2. Bhuva Sachin S.
( GKVK, BANGALORE )
Department of Processing and Food Engineering
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Contents
 Introduction
 Nano-bubbles
 Fundamental properties of NBs
 Generation of NBs
 Important factors influencing the generation of NBs
 Measurement of NBs
 Applications in food processes & products
 Case studies
 Conclusion & Future perspectives
 References

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Introduction  Nano as a emerging science
and technology.
 Father of Nano-technology:
Richard Feynman
Great potential in many manufacturing sectors, such as food,
agriculture polymer and biomedical fields.

5. Top down approach Bottom- up approach
Begin with pattern generated on
a larger scale, then reduced to
nanoscale
Start with atoms or molecules
build up to Nanostructures
By nature, aren’t cheap and quick
to manufacture
Quick to manufacture
Slow and not suitable for large
scale production.
Fabrication is much less expensive
E. g. attrition , milling E. g. Chemical synthesis
Selection of methods depends on
 Type of the material
 Desirable characteristics
 Application
Methods used to make nano-materials
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 Nanobubbles or fine bubbles are small gaseous entities that
are found when solutions are supersaturated with gas.
Nano-bubbles
 Diameter range: 10–200 nm or up to 1000 nm
 NBs - On interfaces (surface) & In bulk solutions (bulk)

7.  Surface NBs are
 found at solid-liquid interface.
 spherical cap shaped bubbles,
 few tens of nanometres in
height, h, and a few hundred
nanometres in width, a.
 Bulk nanobubbles
 found in bulk solutions
 spherical in shape
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10.  Specific Surface Areas
𝑆𝑆𝐴 𝑜𝑓 𝑠𝑝ℎ𝑒𝑟𝑒 =
3
𝑟
 SSA is defined as the total surface area of a
material per unit of solid or bulk volume (units
of m2/m3 or m−1)
 Longer
residence
times
 Fundamental properties of NBs
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11.  Stability and longevity
 Presence & Persistence as stable entity is controversial issue.
 Young–Laplace equation for pressure inside the gas cavities,
𝑃𝑖𝑛 = 𝑃𝑜𝑢𝑡 +
2𝛾
𝑟
Pin = Internal pressure inside bubble
Pout = Pressure of bulk liquid
𝛾 = Liquid surface tension
 Assuming, r = 100 nm, Pout = 105 N/m2 and 𝛾 = 72 mN/m,
Pin = 15 × 105 N/m2
which is about 15 times the atmospheric pressure.
 Higher internal pressure facilitate the rapid dissolution and
disappearance of the bubble within microseconds as per the
Henry's law.
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12.  Henry's law states that the amount of dissolved gas in a liquid
is proportional to its partial pressure above the liquid.
𝐶𝑔 = 𝑘𝑃𝑔
Pg = Partial pressure inside bubble
Cg = Concentration of gas
𝑘 = Henry’s gas constant
Theoretically NBs cannot exist.
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13.  NBs stability dependent on
 Adsorption of anions at interface
(electrostatic repulsive force)
 Higher zeta-potential
 Lower buoyancies forces.
 Hydrogen bonding.
 NBs have a measured lifetimes for hours, days and
even weeks or months
 Excellent stability against coalescence
 Higher solubility of gas in water
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 Zeta potential (ZP) of NBs
 Technique for determining the surface charge of nanoparticles
in solution.
 Potential difference existing between the surface of a bubbles
immersed in a conducting liquid (e.g. water) and the bulk of
the liquid.

15.  Cationic surfactants - positive charged bubbles
 Anionic and non-ionic surfactants - negative charged ZP -
function of gas type, electrolyte properties system, and
chemical surfactants
 Generally negative at pH value of 2–12 15
Constituents Zeta Potential (ζ), -mV
Air 17-20
Oxygen 34-45
Nitrogen 29-35
Carbon dioxide 20-27
 ζ-potential was calculated using Smoluchowski Equation:
ζ =
4𝜋𝜂𝑈
𝜀
ζ = ζ-potential (V); 𝜂 = viscosity of the medium (Pa·s); ε = permittivity of the medium
(F·m-1); v = particle speed (m·s-1); V = voltage applied (V); L = distance of the
electrodes (m)
U =
𝑣
𝑉
𝐿

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 Generation of free radicals
 When NBs are burst, more surface energy is released – high
internal pressure.
 Allowing conversion of O2 molecules into ROS (Reactive
oxygen species).
 OH radicals was created by the collapse of bubbles due to the
accumulation of interfacial ions

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 Generation of NBs
 Methods
 Cavitation
 Electrolysis
 Nano-pore membrane
 Important features of NB generation methods
 Simplicity
 Efficiency
 Scalability
 Low environmental impact
 Low cost of production

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 Cavitation methods
 Most known techniques to produce tiny bubbles filled with gas
 Cavitation is a phenomenon in which rapid changes of
pressure in a liquid lead to the formation of small vapor-filled
cavities in places where the pressure is relatively low
Cavitation
Hydrodynamic
Cavitation
Acoustic
Cavitation

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 Hydrodynamic Cavitation
 When the moving fluid is subjected to pressure reduction,
there is an occurrence of vaporization and generation of
bubbles
 An increase of local pressure will make the generated
bubbles implode, resulting in hydrodynamic cavities.
 Factors affect size of NBs: Pressure and Temperature
 Different geometries - venturi, orifice & throttling valve

20.  Venturi system main parts: inflow, tubule & tapered outflow
 Both gas and liquid
are transferred at the
same time.
 NBs of air with
average diameter from
130 to about 529 nm
were able to be
generated in water via
venturi tube
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 Acoustic Cavitation
 Created by propagating ultrasonic wave through the liquid
 Ultrasonic wave can create gas bubbles via local
compression-expansion cycles
 Average size between 300 and 500 nm

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 Electrolysis method
 Electrolysis of water decompose water into
hydrogen and oxygen gases caused by the electric
potential.
 Production of gas occurs at electrodes.
 If concentration reaches super-saturation level in
the anodic and cathodic streams of the bulk water,
NBs can be generated

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 Membrane method
 Gas phase is pressed through the
pores of the applied membrane into
a flowing aqueous phase
 Size is related to pressure applied.

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Common techniques used to generate NBs and operation parameters

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 Important factors influencing the
generation of NBs
 Pressure
 Hydrodynamic cavitation- critical value increase with
surface tension but also rise turbulent velocity and cavity
collapse violence.
 Higher the pressure, lower the size of NBs.
 Over 3.5 atm pressure, size is almost constant.
 Temperature
 Impact on the liquid physical characteristics including
viscosity, vapour pressure (increase), surface tension and
ability to dissolve gas (decrease).
 Rate of cavitation decrease with rise in temperature.

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 Type and concentration of dissolved gas
 Surface tension, shape stability and tensile strength of bubble
growth is reduced as the solubility of gas is enhanced.
 Surfactant
 Adsorption of surfactant molecules on interphase provide a
protective barrier which help in stability.
 Addition of ionized surfactant or absorption of ionic particles
lead to the shift in ZP values which impacts on the bubbles size
and stability
 Electrolyte solution
 In the electrolyte solution, adsorbed charged ions - electrostatic
repulsion inhibit coalescence.
 Also allow surface tension to decrease the size of bubbles

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 Measurement of NBs
 Dynamic light scattering (DLS)
 Measure size & distribution of nanoparticles (0.5 nm–6 μm)
 Basic principle – Laser beam scattering and fluctuation of
bubbles (Brownian motion).
 Atomic force microscope (AFM)
 Determine information on NB shape at solid-liquid interface.
 Nuclear magnetic resonance (NMR)
 Works based on different magnetic susceptibilities of water
and gases.
 Existence and stability.

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 Applications in food processes &
products
 To improve processability of foods - viscosity reducing effect
– mobility – flow resistance
 Innovative means of seasoning food – permeation and
uniformity
 Improving textural properties and sensory attributes of food –
texture – flavour – digestibility
 Improving health benefit of food – H2, O2 supplement.
 Enhancing freezing and crystallization of food components –
freezing time – crystal size - incrustation

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 Cleaning surface and defouling membrane system – low water
use and flow rate with drop in microbial count
 Antimicrobial properties and water sanitisation – constant
supply of gas - oxidation
 Plant and Aquaculture – germination rate, growth rate
 Froth floatation – Separating hydrophobic materials from
hydrophilic – mineral processing, paper recycling and waste-
water treatment.
 Designing foam products, gel and cream-based foods,
carbonated drinks and nutritional supplement carriers.
 Lakes & Pond Remediation

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Some Recent Applications

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References
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generation and its application in froth flotation (part I): nanobubble generation
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 GHADIMKHANI, A., ZHANG, W., AND MARHABA, T., 2016, Ceramic
membrane defouling (cleaning) by air Nano Bubbles, Chemosphere, 146: 379-
384.
 KIKUCHI, K., NAGATA, S., TANAKA, Y., SAIHARA, Y. AND OGUMI, Z.,
2007, Characteristics of hydrogen nanobubbles in solutions obtained with
water electrolysis, Journal of Electroanalytical Chemistry, 600: 303-310.
 KHANH, K., T., P., TUYEN, T., YONG, W. AND BHANDARIA, B., 2020,
Nanobubbles: Fundamental characteristics and applications in food processing,
Trends in Food Science & Technology, 95: 118–130.

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 LIU, S., OSHITA, S., KAWABATA, S., MAKINO, Y., AND YOSHIMOTO,
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