Stability of Nanobubbles by Quantum Mechanics Thomas Prevenslik QED Radiations Discovery Bay, Hong Kong 1 Topical 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 2 Topical Problems of Fluid Mechanics - Institute of Thermomechanics - Prague - Feb.19-21,2014

Nanobubble on Submerged Surface Topical Problems of Fluid Mechanics - Institute of Thermomechanics - Prague - Feb.19-21,2014 r S = nm, h = nm, 3 Pinning

What is the mechanism of Nanobubble Stability? Topical Problems of Fluid Mechanics - Institute of Thermomechanics - Prague - Feb.19-21,2014 4

Gas Diffusion Bubble Pinning Charge Repulsion Others Proposed Mechanisms Topical Problems of Fluid Mechanics - Institute of Thermomechanics - Prague - Feb.19-21,2014 5

Gas Diffusion* Topical Problems of Fluid Mechanics - Institute of Thermomechanics - Prague - Feb.19-21,2014 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)

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

Charge Repulsion* Topical Problems of Fluid Mechanics - Institute of Thermomechanics - Prague - Feb.19-21,2014 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 8

Problem 9 Topical Problems of Fluid Mechanics - Institute of Thermomechanics - Prague - Feb.19-21,2014

Hypotheses Topical Problems of Fluid Mechanics - Institute of Thermomechanics - Prague - Feb.19-21, Nanobubbles dissociate H 2 O 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 H 2 O is instead caused by the ubiquitous nanobubble. *MD simulation by M. Parrinello in Autoionization in Liquid Water. Science, vol. 291 (2001) pp

Topical Problems of Fluid Mechanics - Institute of Thermomechanics - Prague - Feb.19-21,2014 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 12 Nanobubble (E  0) kT Macrobubble (E = kT) QM Topical Problems of Fluid Mechanics - Institute of Thermomechanics - Prague - Feb.19-21,2014 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 13 Topical Problems of Fluid Mechanics - Institute of Thermomechanics - Prague - Feb.19-21,2014

QM, kT Energy, and QED Topical Problems of Fluid Mechanics - Institute of Thermomechanics - Prague - Feb.19-21,2014 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 Topical Problems of Fluid Mechanics - Institute of Thermomechanics - Prague - Feb.19-21,

Results Topical Problems of Fluid Mechanics - Institute of Thermomechanics - Prague - Feb.19-21, Spherical Bubble in Bulk Bubble on Submerged Solid

Conclusions 17 Topical Problems of Fluid Mechanics - Institute of Thermomechanics - Prague - Feb.19-21,2014 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 Topical Problems of Fluid Mechanics - Institute of Thermomechanics - Prague - Feb.19-21,2014