Nanobubble Collapse on a Silica Surface in Water: Billion-Atom Reactive Molecular Dynamics Simulations

Adarsh Shekhar, Ken-ichi Nomura, Rajiv K. Kalia, Aiichiro Nakano, and Priya Vashishta

Phys. Rev. Lett. 111, 184503 – Published 31 October 2013

Abstract

Cavitation bubbles occur in fluids subjected to rapid changes in pressure. We use billion-atom reactive molecular dynamics simulations on a 163 840-processor BlueGene/P supercomputer to investigate damage caused by shock-induced collapse of nanobubbles in water near an amorphous silica surface. Collapse of an empty bubble generates a high-speed nanojet, which causes pitting on the silica surface. We find pit radii are close to bubble radii, and experiments also indicate linear scaling between them. The gas-filled bubbles undergo partial collapse and, consequently, the damage on the silica surface is mitigated.

Received 19 June 2013

DOI:https://doi.org/10.1103/PhysRevLett.111.184503

Authors & Affiliations

Adarsh Shekhar, Ken-ichi Nomura, Rajiv K. Kalia, Aiichiro Nakano, and Priya Vashishta^*

Collaboratory for Advanced Computing and Simulations, Department of Chemical Engineering and Materials Science, Department of Physics and Astronomy, and Department of Computer Science, University of Southern California, Los Angeles, California 90089-0242, USA

^*To whom all correspondence should be addressed.

Article Text (Subscription Required)

Click to Expand

Supplemental Material (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 111, Iss. 18 — 1 November 2013

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
(a) Schematic diagram of the initial setup of the system. Oxygen and hydrogen atoms in water are shown as blue and cyan dots, respectively. (b) Snapshot of the system at time $t = 5 ps$ . In the central slice through the silica slab, the color green represents normal water and dark blue is the incoming shock wave in water. The bubble surface is shown in blue.Reuse & Permissions
Figure 2
(a) Partially collapsed nanobubble under the influence of shock wave at time $t = 20 ps$ . (b) Water nanojet formed during shock-induced collapse of the nanobubble. The silica slab is shown in yellow. The central slice across the silica slab is color coded by the magnitude of the velocity of water molecules. The velocity field lines show a focused jet of water molecules. (c) Number of $H_{3} O^{+}$ species along the central slice of the system. $H_{3} O^{+}$ ion production increases significantly when the nanojet hits the distal side of the bubble at time $t = 25 ps$ . (d) Pressure profile in water at $t = 30 ps$ shows a secondary shock wave.Reuse & Permissions
Figure 3
(a) Snapshot of cavitation damage in the silica slab due to nanobubble collapse at time $t = 50 ps$ . (b) Spatial distribution of $H_{3} O^{+}$ ions in the water nanojet. (c) Pressure profile at $t = 50 ps$ shows the reflected shock wave in water. The peaks in (b) correspond to the high-pressure region in (c).Reuse & Permissions
Figure 4
(a) Volumes of cavitation pits in systems with nanobubbles of diameter 40 (red) and 97.6 nm (blue). (b) Snapshot shows atoms at the pit edge of the silica slab in the system with $10^{9}$ atoms. Silicon-oxygen bonds are yellow-orange, and cyan spheres represent hydrogen atoms inside the silica slab. Blue spheres represent oxygen atoms in water molecules within 0.5 nm from the silica slab. (c) Silanol distribution in the silica slab as a function of the distance from the pit center for bubbles of diameters 40 (red) and 97.6 nm (blue). The pit center is defined as the center of the projection of the cavitation pit on the plane normal to the shock direction.Reuse & Permissions
Figure 5
(a) Shock-induced deformation of a gas-filled nanobubble and the pressure distribution in a cross section of the system. (b) Snapshot of vortex rings at the periphery of the nanobubble. Streamlines represent molecular velocities, and the inset shows the velocity field of water molecules (black arrows) around the edge of the deformed bubble. (c) Number of $H_{3} O^{+}$ ions per ${nm}^{3}$ around the partially collapsed gas-filled bubble at time $t = 50 ps$ .Reuse & Permissions

Physical Review Letters