Xenon and Krypton Dissolved in Water Form Nanoblobs: No Evidence for Nanobubbles

We demonstrate, experimentally and by molecular dynamics simulations, that krypton and xenon form nanostructured water-gas domains. High pressure was applied to force the inert gases to dissolve in water following Henry’s law, then the liquid was depressurized, centrifuged, and inspected by dynamic light scattering. The observed objects have similar sizes and electrical properties to nanobubbles, but we found that they have fairly neutral buoyancy even at high gravitational fields. We posit that the formed nano objects are not bubbles but blobs, unique structures conceived as clathrate-hydrate precursors, thus resolving the so-called Laplace pressure bubble catastrophe.

Figure 1

(a) Schematic of the pressure apparatus. 1. Gas cylinder, 2. needle valve, 3. pressure gauge, 4. stainless steel cylindrical tube, 5. hydraulic jack, 6. rubber stopper, 7. glass vial. (b) $P$ vs $V$ for the ideal gas and experiment ($n=3$).

Figure 2

(a) Correlograms of Kr and Xe nanodomains before and after centrifugation (4200 G, for 2 h). (b) Size distributions of Kr and Xe nanodomains before and after centrifugation (4200 G, for 2 h). At least three experiments were performed, where the shown error bars are standard errors. (c) Residence times of the nanodomains subjected to a gravitational field of 4200 G. (d) Schematic of blob structures.

Figure 3

Radial distribution functions of Kr and Xe obtained by molecular dynamics simulations for various concentrations: 35, 40, 45, 50, and 200 water molecules per guest atom. Note that for Kr all $g(r)$’s match. However, for Xe, the radial distribution functions at 35 and 40 water molecules per atom drastically modify, indicating the emergence of nanobubbles, as observed in Fig. S7 [48]. The peaks in the $g(r)$’s correspond to the events schematically represented in both panels.