Nanocapillarity and the liquid bridge mediated force between colloidal nanoparticles

In this work we probe the concept of interface tension for ultra thin adsorbed liquid films in the nanoscale by studying the surface fluctuations of films down to the monolayer. Our results show that the spectrum of film height fluctuations of a liquid-vapor surface may be extended to ultra thin films provided we take into account the interactions of the substrate with the surface. Global fluctuations of film height are described in terms of the disjoining pressure, while surface deformations that are proportional to the interface area are accounted for by a film thick dependent surface tension. As a prove of concept, we model the capillary forces between colloidal nanoparticles held together by liquid bridges. Our results indicate that the classical equations for capillarity follow very precisely down to the nanoscale, provided we account for the film height dependence of the surface tension