Effect of roughness on wettability and floatability:Based on wetting film drainage between bubbles and solid surfaces

Wetting film thinning measurement was introduced to clarify the wettability and floatability of solid surfaces with varying roughness. The wettability was quantified using the contact angle measurement combined with the dynamic force microbalance test between solid surfaces and water droplets, while the floatability was investigated by the bubble-solid surface dynamic attachment observation and the induction time measurement. The results show that the water contact angles reduce(14.53°, 12.74°, and 6.71°)with the increase of glass surface roughness, while the water droplet-glass adhesion forces intensify(11.1, 19.1 and 19.2 μN) owing to the stable wetting film. The distortion of the contact surface and the Wenzel state are the causes. In contrast, the hydrophobized surfaces have the growing apparent contact angles(38.08°, 69.81°, and 81.01°), declining adhesion strength and shortening induction time(863, 352and 12 ms) along with the increasing surface roughness. The weak wettability and fine floatability on the rough hydrophobized surface is reflected in the fast wetting film drainage dynamics and three-phase contact formation, which may be attributed to the wetting film with short diameter on tiny rough nubs and the entrapped air in the grooves as a bridge between the bulk bubble and the solid surface.

Quantitative prediction of residual wetting film generated in mobilizing a two-phase liquid in a capillary model

This research studies the motion of immiscible two-phase liquid flow in a capillary tube through a numerical approach employing the volume of fluid method,for simulating the core-annular flow and water flooding in oil reservoirs of porous media.More specifically,the simulations are a representation of water flooding at a pore scale.A capillary tube model is established with ANSYS Fluent and verified.The numerical results matches well with the existing data available in the literature.Penetration of a less viscous liquid in a liquid of higher viscosity and the development of a residual wetting film of the higher viscosity liquid are thoroughly investigated.The effects of Capillary number,Reynolds Number and Viscosity ratio on the residual wetting film are studied in detail,as the thickness is directly related to the residual oil left in the porous media after water flooding.It should be noticed that the liquids considered in this research can be any liquids of different viscosity not necessarily oil and water.The results of this study can be used as guidance in the field of water flooding.

Morphology of liquid drops and thin films on a solid surface with sinusoidal microstructures

Surface microstructures of solid materials play a significant role in various wetting and dewetting phenomena. In the present paper, the effect of micro- and nano-structures of a substrate surface on the morphology and evolution of liquid droplets and thin films is examined. The governing equations satisfied by droplets and films on a sinusoidal surface are derived by considering van der Waals force, surface tension, gravity and hydrostatic pressure. The morphologies of both liquid droplets and thin films are numerically simulated under various characteristic sizes of roughness. It is found that the droplet shapes show a significant dependence upon the characteristic sizes of substrate microstructures. A thin liquid film on a hydrophilic substrate may have a horizontal surface or replicate the substrate morphology, depending on the wavelength of roughness.