Effect of Surface Heterogeneities on Interactions between Air Bubbles and Heterogeneous Surfaces.

The effects of surface heterogeneities on bubble-particle interactions have received little attention although heterogeneities are common for varieties of substance surfaces. In this work, heterogeneous surfaces consisting of discrete hydrophilic dots on a hydrophobic background were fabricated. The interactions between air bubbles and heterogeneous surfaces with different hydrophilic area fractions were investigated using a high-sensitivity microbalance coupled with a high-speed video camera. It was found that the snap-in, maximum adhesion, and pull-off forces increased as the hydrophilic area fraction decreased. These experimental results were compared with the calculated interaction forces. The comparison between experimental results and the calculated interaction forces showed that the normalized contact line length (δ) should be considered in the calculation of the snap-in force, and its value was between 1 and the δ value corresponding to the maximum pinning strength. In contrast, δ = 1 is more appropriate for the calculation of maximum adhesion force, indicating that the corrugations in the three-phase contact line could be neglected. These findings demonstrate that discrete hydrophilic defects make bubble-surface attachment difficult but have nearly no effect on bubble-surface detachment. Better understanding of the interactions between air bubbles and heterogeneous surfaces potential offers a new thought to control the bubble-particle interactions using appropriately design of particle surfaces.