New insights into the contact angle and formation process of nanobubbles based on line tension and pinning

In this paper, the effect of a probe tip on the contact angle measurements and the formation process of nanobubbles based on line tension and pinning theory was investigated. In this investigation, the images of nanobubbles and micropancakes on mica(001) and molybdenite(0001) surfaces were obtained during an alcohol-water exchange by means of atomic force microscopy (AFM) in tapping mode (TMAFM). Based on the image characteristics and the theory of line tension and pinning, a new point of view is presented: the contact angle of a nanobubble is not always a large obtuse angle but is an uncertain value; its true value is affected by the curvature radius of the AFM probe tip, and the value is close to the macroscopic contact angle. Meanwhile, the formation of nanobubbles is affected by the surface tension, line tension and pinning.