Surface tension of cavitation bubbles

Cavitation occurs in porous materials when pores are connected to the outer gas reservoir by small constrictions. We have developed a simple technique to obtain such ink-bottle pores in monolithic porous silicon and porous alumina membranes. When the pore diameter is larger than about 10 nm, such materials empty through homogeneous cavitation, as recently demonstrated using hexane at room temperature¹.

We report on the cavitation of nitrogen and helium in a wide temperature range. The pressure threshold for cavitation is consistent with classical nucleation theory. However, at low temperature, the threshold is slightly higher than predicted. This shift is usually attributed to a decrease of the surface tension with the curvature of the liquid-vapor interface. In this interpretation, we find that the surface tension is reduced by 20% when the radius of the critical bubble is about 1 nm, a value consistent with experimental results in bulk superheated nitrogen.

Taking advantage of the huge number of independent pores, we have measured the nucleation rate for nitrogen as a function of the pressure in the vicinity of the cavitation threshold. This allows us to determine the correction to the surface tension up to second order in curvature for temperatures in the range 65 - 100 K. Such measurements in a simple liquid open the route to testing precisely theoretical models for curved liquid-vapor interfaces².

 

1. V. Doebele, et al, Phys. Rev. Lett. 125 (2020) 255701.

2. N. Bruot, F. Caupin, Phys. Rev. Lett. 116 (2016), 056102.