Wetting of Silicone Oil Drops and Air Bubbles in Ethylene Glycol/Water Mixtures

Contact
angles of silicone oil droplets and air bubbles settled
on a solid substrate and confined in binary ethylene glycol/water
mixtures were studied as a function of ethylene glycol concentration.
Despite similar reductions in interfacial tensions for both systems,
distinct wetting behaviors were observed. While the air bubble contact
angle increased with ethylene glycol concentration, the silicone oil
droplet exhibited a more complex response, characterized by a stable
contact angle at low ethylene glycol concentrations followed by an
increase at higher concentrations. This suggests that droplet morphology can remain relatively
stable even as interfacial tensions change. A phenomenological description
based on the imbalanced forces highlights the crucial role of the
contact angle in pure water environment, in predicting the wetting
behavior that may follow the reduction of interfacial tension by further
surfactant or cosolvent adsorption.