Probing the hydrophobic interaction between air bubbles and partially hydrophobic surfaces using atomic force microscopy

The hydrophobic interaction plays an essential role in various natural phenomena and industrial processes. Previous studies on the hydrophobic interaction focused mainly on the interaction between hydrophobic solid surfaces for which the effective range of hydrophobic attraction was reported to vary from ∼10 nm to >1 μm. Here, we report studies of the interaction between an air bubble in water used as a probe attached to the cantilever of an atomic force microscope and partially hydrophobized mica surfaces. No bubble attachment was observed for bare hydrophilic mica, but attachment behaviors and attraction with an exponential decay length of 0.8-1.0 nm were observed between the air bubble and partially hydrophobized mica as characterized by a water contact angle on the mica surface that varied from 45° to 85°. Our results demonstrate the important roles of the additional attraction at partially hydrophobized surfaces and hydrodynamic conditions in bubble attachment to substrate surfaces and provide new insights into the basic understanding of this interaction mechanism in various applications such as mineral flotation.