Liquids at negative pressure

Abstract

We have further explored the final stages of the collapse of an unstable cavity or bubble using the Molecular Dynamics computer simulation technique. A nanometre sized spherical volume of molecules was removed from a bulk Lennard -Jones liquid, which being mechanically and thermodynamically unstable, proceeded to collapse. The molecules with the highest kinetic energy were the first to enter the initially empty cavity. The temperature of individual molecules inside the cavity, while the density was still typical of a gas, could reach at least an order of magnitude larger than that of the surrounding liquid, e.g., equivalent to 6, 000 K for water, which is not unreasonable for the sonoluminescence effect to be seen. During the filling in of the cavity, the average temperature decreased, as the contents thermally equilibrated with the surrounding liquid. The bubble partially filled in, and then proceeded to partially empty again, and so on in an oscillatory manner, with ever decreasing amplitude towards the final uniform liquid state. This 'recoil' effect is predicted by classical hydrodynamic treatments and has been observed in experiment for much larger bubbles. The temperature, density and normal pressure component were resolved as a function of radius from the centre of the bubble at selected times during the collapsing process. The simulations support the view that MD can provide a realistic representation of the final stages of cavity collapse. It does not make assumptions about equation of state and transport coefficients as would be required for a comparable solution of the Navier -Stokes hydrodynamics equations, and is therefore an especially appropriate description for the final stages of the collapse.

Comparison of heterogeneous and homogeneous bubble nucleation using molecular simulations

“…The size dependence of the surface tension should lead to an underestimate of nucleation rates by the classical theory. 40 The fact that our results matched the classical theory results better than those mentioned above is probably due to the surface tension and state point we used. Without data at other state points and a better estimation of surface tension, no general conclusion about the accuracy of the classical theory can be derived from this work.…”

Mesoscopic modelling of microbubble in liquid with finite density ratio of gas to liquid

“…The inside bubble pressure is a little larger than the outside liquid pressure to balance the effect of surface tension. We also capture the pressure fluctuations around the interface, which may be caused by the strong interactions between bubble particle and liquid particle, in detail, there is a transition region (finite width of interface) mixed with both bubble particles and liquid particles, particles are stretched in this region making them in a metastable state [28] and a similar phenomenon was also presented by MD simulation [29]. With the values of the inside and outside pressure, coupling with the Young-Laplace equation (eq.…”

Solid–fluid phase transitions under extreme pressures including negative ones

“…In auxetic materials (like zeolites and various polymeric foams [2]) the appearance of tri-axial negative pressure upon uni-axial stretch is an inherent behavior, due to the volume expansion. Another link between the auxetic behavior and negative pressure states has been described, for the first time independently, by Boal et al, Wojciechowski et al, and others [4][5][6][7][8][9] showing that even ordinary materials can be auxetic at an isotropic tension i.e. at negative pressure.…”