Observation of relaxation of the metastable state of a non-wetting liquid dispersed in a nanoporous medium

Abstract

The disordered system of pores in a random nanoporous medium can be filled with a non-wetting liquid at excess pressure. It has been established that, when the porous medium is completely filled and excess pressure is then removed, a part of the liquid can remain in the disordered porous medium. This means that the state of the confined non-wetting liquid is an effectively “wetting” (metastable) state in the disordered confinement of the porous medium. The metastable state relaxation of the confined non-wetting liquid dispersed in the disordered nanoporous medium has been experimentally observed for systems consisting of water and grafted silica gels. In this work, time and temperature dependences of the volume fraction of the non-wetting liquid dispersed in the nanoporous medium have been obtained for three grafted nanoporous media (Libersorb 23, Fluka 100 C18 and Fluka 100 C8) with different pore size distribution functions (PSDs). It has been shown that the PSD, (liquid–grafted solid surface) interaction and temperature strongly affect the experimental dependences obtained. The time dependences of the volume fraction of the non-wetting liquid have been approximated by power law functions for different temperatures. The volume fraction of the confined liquid decreases in time according to a power law as was predicted in [V.D. Borman et al., Phys. Rev. E 88, 052116 (2013)]. Thus, the observed relaxation of the metastable state can be described as a discrete equilibrium process with the overcoming of numerous local maxima appearing because of random local configurations of filled and empty pores with various sizes in the disordered porous medium.