Stability of Nanobubbles by Quantum Mechanics Thomas Prevenslik QED Radiations Discovery Bay, Hong...

Stability of Nanobubbles by

Quantum Mechanics

Thomas PrevenslikQED Radiations

Discovery Bay, Hong Kong

1Topical Problems of Fluid Mechanics - Institute of Thermomechanics - Prague - Feb.19-21,2014

Air bubbles grow or shrink depending on the air dissolved in the bubble wall. Solubility of air is proportional to the Laplace

pressure that increases as the diameter decreases the bubbles dissolve in a few microseconds.

However, nanobubbles are observed to be stable on submerged surfaces for days, defying the expectation of

prompt dissolution

Introduction


Nanobubble on Submerged Surface

Topical Problems of Fluid Mechanics - Institute of Thermomechanics - Prague - Feb.19-21,2014

rS = 25 - 1000 nm, h = 5 - 20 nm,

3

Pinning

What is the mechanism of Nanobubble Stability?


4

Gas Diffusion

Bubble Pinning

Charge Repulsion

Others

Proposed Mechanisms


5

Gas Diffusion*


Slow rate of dissolution of bubble air into the liquid wall

Air cannot enter the liquid unless transferred through the entire liquid. Depending on the thickness of the liquid, the dissolution

may take many hours rather than fractions of a second.

Problem: Slow dissolution should show the bubbles ever so slightly shrinking over time, but this is not observed.

*Brenner, M. P. & Lohse, D.: Dynamic Equilibrium Mechanism for Surface Nanobubble Stabilization. PRL, vol. 101 (2008) 214505.

6

Bubble Pinning*


Slow dissolution by pinning of the three-phase boundaries

Pinning reduces the Laplace pressure during dissolution opposite to that for free bubbles in bulk water

Problem: There is no pinning in free bubbles, yet free bubbles are observed to have long lifetimes.

*Zhang, X., Chan, D. Y. C., Wang, D. and Maeda, N.: Stability of Interfacial Nanobubbles. Langmuir, vol. 29 (2013) pp. 1017.

7

Charge Repulsion*


Like (+ or -) charges present in the bubble

Charge repulsion opposes the minimization of bubble area by surface tension.

Source of charge is auto-ionization of water

Hydroxyl OH ions in bubble and hydronium H ions in wall

Charge repulsion is most likely stability mechanism

*Chaplin, M.: See information and analysis of charge stablized nanobubbles http://www.lsbu.ac.uk/water/nanobubble.html

8

http://www.lsbu.ac.uk/water/nanobubble.html




Self-ionization of water H2O → H+ + OH− given in Boltzmann distribution depends on the activation energy ΔE

Classical physics at 300K kT = 0.0258 eV. For ΔE = 12.6 eV , N/No 0

One H2O molecule dissociates every 10 hours.

But by QM, the H2O molecule never dissociates as kT 0

QM = quantum mechanics

Problem: Self-ionization cannot sustain the robust charging observed in the stability of nanobubbles.

Problem


Hypotheses


Nanobubbles dissociate H2O molecules

Mobility of H ions > OH ions H ions move into the bubble wall to increase the pH of water leaving OH ions in bubble.

Stability of nanobubbles is caused by the repulsion of hydroxyl OH ions in the bubble that opposes bubble

collapse by surface tension.

The pH of water thought* caused by self-dissociation of H2O is instead caused by the ubiquitous nanobubble.

*MD simulation by M. Parrinello in Autoionization in Liquid Water. Science, vol. 291 (2001) pp. 2121-2124.


Nanobubble stability finds basis in the QM requirement that the kT energy of the water molecule vanishes under the TIR

confinement of the nanobubble.

TIR = total internal reflection

Classical physics is assumed in the stability mechanisms of Diffusion , Pinning, and Charge repulsion

What about QM?.

11

Nanobubble Stability

QM Restrictions

1 10 100 10000.00001

0.0001

0.001

0.01

0.1

TIR Wavelength - l - microns

Pla

nck

Ene

rgy

- E

- e

V

1

kT

hcexp

hc

E

12

Nanobubble (E 0)

kT Macrobubble (E = kT)

QM


kT energy is available in macrobubbles, but not nanobubbles

Classical Physics

In 1870, Tyndall showed photons are confined by TIR in the surface of a body if the refractive index of the body

is greater than that of the surroundings.

Under TIR confinement, QED induces the kT energy of the water molecules that enter the bubble to create TIR photons that travel

around the circumference of the bubble surface.

f = ( c/n ) / = D E = hf

D = bubble diameter

TIR Confinement


QM, kT Energy, and QED


The water molecule on the bubble surface has kT energy as the molecule is part of the macroscopic bubble wall.

But once the water molecule enters the TIR confinement of the bubble, the kT energy vanishes by QM

Lacking kT energy, the water molecule cannot conserve the loss of kT energy by a change in temperature. So,

QED conserves the loss by creating TIR photons.

14

Stability


Surface tension pressure PST is,

where, is the surface tension and R is the bubble radius.

The charge pressure Pcharge is,

where, o is the permittivity. Equating pressures,

= 2.55x10-12 C/m2 0.1[e- / nm2]2 nm

15

Results


16

1 10 1000

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0

200

400

600

800

1000

1200

1400

1600

Spherical bubble diameter - d – nm

OH

- D

ensi

ty -

-

e- /n

m2

Num

ber

Nio

nser

OH

- io

ns

Nions

Spherical Bubble in Bulk

1 10 1001

10

100

1000

Bubble height - h - nm

TIR

Pla

nck

Ene

rgy

- E

- e

V

Uionize

Bubble on Submerged Solid

Conclusions


Nanobubble stability by the charge repulsion of surface tension is supported by QED induced hydroxyl ions from the QM conservation of kT energy of water molecules that enter

the TIR confinement of the bubble.

QED induced ionization does produce a high number density of hydroxyl ions, but recombination is also very high. Supporting analysis is difficult as the net charge density for

bubble stability is small. Experiments appear more feasible.

QM precludes auto-ionization of water as the source of hydronium ions that give the pH of water.

Instead, the ubiquitous nanobubble is the source of pH

Questions & Papers

Email: [email protected]

http://www.nanoqed.org


http://www.nanoqed.org/

Stability of Nanobubbles by Quantum Mechanics Thomas Prevenslik QED Radiations Discovery Bay, Hong...

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