2. Bhuva Sachin S.
( GKVK, BANGALORE )
Department of Processing and Food Engineering
2
3. 3
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
4. 4
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
5
6. 6
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
7
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
10
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.
11
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.
12
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
13
14. 14
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
16. 16
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
17. 17
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
18. 18
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
19. 19
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
20
21. 21
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
22. 22
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
23. 23
Membrane method
Gas phase is pressed through the
pores of the applied membrane into
a flowing aqueous phase
Size is related to pressure applied.
25. 25
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.
26. 26
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
27. 27
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.
28. 28
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
29. 29
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
31. 31
References
FAN, M., TAO, D., HONAKER, R., AND LUO, Z., 2010, Nanobubble
generation and its application in froth flotation (part I): nanobubble generation
and its effects on properties of microbubble and millimetre scale bubble
solutions, Mining Science and Technology, 20: 1-19.
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.
32. 32
KUKIZAKI, M. AND GOTO, M., 2006, Size control of nanobubbles
generated from Shirasu-porous-glass (SPG) membranes, Journal of Membrane
Science, 281: 386-396.
LIU, S., OSHITA, S., KAWABATA, S., MAKINO, Y., AND YOSHIMOTO,
T., 2016, Identification of ROS Produced by Nanobubbles and Their Positive
and Negative Effects on Vegetable Seed Germination, Langmuir, 32: 11295-
11302.
SEDDON, J. R. T., LOHSE, D., DUCKER, W. A., AND CRAIG, V. S. J.,
2012, A Deliberation on Nanobubbles at Surfaces and in Bulk,
ChemPhysChem, 13(8): 2179–2187.
UCHIDA, T., LIU, S., ENARI, M., OSHITA, S., YAMAZAKI, K., AND
GOHARA, K., 2016, Effect of NaCl on the Lifetime of Micro- and
Nanobubbles, Nanomaterials, 6.
ZHU, J., HONGJIE, A., ALHESHIBRI, M., LIU, L., PAUL, M., J., T., LIU,
G., AND VINCENT, S., J., C., 2016, Cleaning with Bulk Nanobubbles,
Langmuir, 32: 11203-11211.