Microscale wetting effect of oil-water in silica microtubes

Abstract

Pore wetting is significant for understanding fluid behaviour in porous media. Due to the lack of measurement techniques, pore wettability was estimated by using contact angles measured on flat plate. This results in that the effect of pore size on wettability is rarely studied. In this paper, the oil-water static contact angles in the silica microtubes with inner diameter (ID) range of 1–523 μm were measured by the cryo-Focused Ion Beam-Scanning Electron Microscopy (cryo-FIB-SEM) and optical microscope. The experimental results show that the oil (silicone oil, hexadecane) and water contact angles in the silica microtubes have the microscale wetting effect, that is the contact angles increase monotonically with the decrease of the microtubular ID. Moreover, the oil-water contact angle of water-filled first is always smaller than that of oil-filled first. The static pore contact angle of oil-water in a silica microtube is different from the contact angle on a silica plate. This paper adds to our current understanding of the pore scale wettability phenomenon in the porous media and provides us with an experimental method for measuring micron scale pore wettability.