The capillarity equation at the nanoscale: Gas bubbles in metals

We investigate the modifications to the Young-Laplace capillarity equation needed to describe nanoscale gas bubbles embedded in metals, scale at which the finite width of the interface region cannot be neglected. We focus in particular on the case of He in Fe. Using both, the concept of Tolman's length that provides a curvature dependence for the interface energy, and a new equation of state for He at the nanoscale that accounts for interface effects (see Caro et al., 2013), we derive an expression to predict pressure, and from it density and the amount of He in nanoscale bubbles. We find that conditions for equilibrium are found for values of pressure or density at variance by a factor of ∼2 compared to the traditional way of using the capillarity equation and a bulk He EOS.