On the Role of Nanometer Scale Structure on Interfacial Energy

Natural surfaces are often structured with nanometre-scale domains, yet a framework providing a quantitative understanding of how nanostructure affects interfacial energy, γSL, is lacking. Conventional continuum thermodynamics treats γSL solely as a function of average composition, ignoring structure. Here we show that, when a surface has domains commensurate in size with solvent molecules, γSL is determined not only by its average composition but also by a structural component that causes γSL to deviate from the continuum prediction by a substantial amount, as much as 20% in our system. By contrasting surfaces coated with either molecular (<2 nm) or larger scale domains (>5 nm), we find that while the latter surfaces have the expected linear dependence of γSL on surface composition, the former exhibit a markedly different non-monotonic trend. Molecular dynamics simulations show how the organization of the solvent molecules at the interface is controlled by the nanostructured surface, which in turn appreciably modifies γSL.