An experimental study on dynamic pore wettability

Dynamic pore wettability is important for understanding fluid behavior and adsorption in porous media for enhanced oil recovery, groundwater movements, nanofluidics and nanolubrication. Although dynamic wetting of different liquids has been extensively studied on various plane substrates, dynamic wettability in small pores has not been systematically investigated. In this paper, we measured dynamic contact angles in single glass capillaries with a size range from 100 to 250μm, in order to investigate the relationship between dynamic contact angle and spontaneous imbibition of various liquids, the effects of surface tension and viscosity of liquids on dynamic contact angle, and the dependence of contact angle on contact-line velocity in a pore. The liquids used are silicone oils with various viscosities, deionized water, 1-propanol, n-decane, crude oil, propanol-water mixtures with various surface tensions. The results indicate that the dynamic contact angle of liquids in a pore increases monotonically with the contact-line velocity at low capillary numbers, and this increase becomes more significant when more viscous liquids or liquids with lower surface tensions are used. A new empirical correlation based on the obtained experimental data has been proposed to describe dynamic pore wettability in a low capillary number range (1.0×10^-7<Ca<1.8×10^-5). Finally, we show that all our results can be summarized by a master curve relating the contact angle variation at a specific velocity with the Crispation number (Cr) signifying the importance of the interfacial deformation of liquid in a pore.