Experimental study on the effect of tube diameter on gas–liquid wettability in silica microtubules

Abstract

In this paper, the gas–liquid static contact angles in silica microtubes (inner diameter range of 5–700 μm) are measured by optical microscope. The experimental results show that the gas–liquid contact angles in the microtube have microscale wetting effect, which decrease monotonically with the decrease of the tube diameter and regularly deviate from the contact angle measured on the plate. When the tube diameter decreases from 700 μm to 5 μm, the contact angles of water and hexadecane decrease from 42.87° to 13.22° and 15.94°–9.09°, respectively. Actual microscale wetting effect causes the gas–liquid capillary force and driving resistance of residual droplets in pore-throat to be bigger than the value determined by the contact angle on the plate. The smaller the pore radius, the greater the influence of the microscale wetting effect on the capillary force. The larger pore-throat ratio and smaller throat radius, the greater influence of the microscale wetting effect on the driving resistance. These results advance our current understanding of wettability in porous media and offer us directly measured contact angles from pore scale which are better representation of actual pores than flat plate to characterize the fluid wettability in porous media.

Keywords

• Wettability
• Capillary force
• Microscale effect
• Contact angle
• Silica microtubules