Role of Surface Charge and Hydrophobicity in the Three-Phase Contact Formation and Wetting Film Stability under Dynamic Conditions

Abstract

Determination and control of the parameters influencing three-phase contact formation and wetting film stability under dynamic conditions is important for both industrial applications and fundamental studies. Hydrophobicity profoundly affects not only the critical thickness of rupture but also the subsequent rate of the three-phase contact expansion. On the other hand, surface charge has a significant impact on the wetting film stability.In the present study, by comparing collision of air bubbles of different sizes with hydrophobized amorphous titanium dioxide (TiO2) surfaces immersed into solutions at different pH values, we demonstrated that for an intermediate degree of hydrophobicity (advancing contact angle ≤ 60°), the surface charge becomes a decisive factor determining the time of the three-phase contact formation, tTPC, and the time of wetting film drainage, td. For pH values below the isoelectric point (IEP) of TiO2, the tTPC and td were significantly shorter than for pH values above the IEP. Mor...