Nanometer-scale wetting transitions in mesopores: a SAXS analysis

The equilibrium and metastable configurations of confined binary liquids has been a topic of research since the early work of Liu et al. in the nineties [1]. In particular, it has been proposed theoretically that liquids may coexist inside nanopores in the form of layers covering uniformly the solid surface, of plugs filling locally the pore space, or of capsules floating in the middle of the pores.
In the present contribution, we report in situ synchrotron small-angle scattering (SAXS) experiments on hexane/nitrobenzene solutions confined in mesoporous carbon xerogels [2]. The SAXS shows that these systems exhibit reversible temperature-induced transitions between the layer and the plug configurations. The scattering data is analyzed using a so-called plurigaussian model, which enables us to reconstruct the configurations of the confined liquids, and quantitatively analyze the wetting transitions at the nanometer-scale in terms of changing interface areas, contact angles, and triple-line lengths.