A bulk thermodynamic theory of the surface: Predicting quasiliquid layer thicknesses from neon to aluminum

Bryan F. Henson, LANL, C-PCS

Many are familiar with the microscopic layer of water that coats ice below the freezing point, enabling ice skating and responsible for thunderstorm electrification and frost heave.  Fewer will know that the same phenomenon has been observed on other materials such as solid neon at 25 K and aluminum at 933 K.  This coexistence of solid and liquid below the freezing point has been the source of much debate as it was believed (and taught in college courses) since the late 19th century work of the great American chemist Willard Gibbs that three phases of a single material, solid, liquid and gas, could not coexist together except at a single temperature.  Enrico Fermi was the first to point out that the answer to the paradox of this liquid layer lies in the inclusion of the energy of the surface in the equations of the chemical potential first deduced by Gibbs.  Now we have come full circle by showing that this surface energy is a function of the difference in the energies of the solid and liquid phases, and that all materials observed to date, from neon and ice to aluminum, exhibit this phenomenon in the same way. We show that when viewed as a single phenomenon, essentially all published measurements of the quasiliquid layer thickness as a function of temperature on solids below the melting point may be plotted as two universal functions of the ideal liquid activity.¹  The two classes of behavior that are observed distinguish molecular and atomic systems.  We derive this universal dependence on activity through a grand canonical lattice calculation.  This is the only such unifying theory of this phenomenon. 

Additionally, we have performed nonlinear light scattering measurements on the H₂O ice/liquid system and, although the data are preliminary, we have observed for the first time the asymptotic divergence of the thickness at temperatures other than the triple point.  This observation has significant implications for the physical understanding of the phenomenon, which will be discussed.

1      B.F. Henson and J.M. Robinson, Phys. Rev. Lett. 92, 246107 (2004).

The P/T Colloquium is
typically held each
Thursday, 3:45–5:00 PM.
Refreshments are served
at 3:15 PM.