Morphological and force spectroscopy characterizations for indentification of surface nanobubbles from nanodroplets and blisters

Abstract

Surface nanobubbles (NBs) play an important role in various practical applications, such as mineral flotation and separation, drag reduction, and nanostructured surface fabrication. Until now, it still remains as a challenge to identify surface NBs from other spherical-cap-liked nano-objects, like blisters and nanodroplets (NDs). Here we focus on the distinctions of NBs from NDs and blisters using an atomic force microscopy. It is implemented through morphological characterization, high load scanning, and force spectroscopy measurement. In the morphological characterization experiment, contact angles of the three types of nano-objects were compared. In the high load scanning experiment, the response of the nano-objects to high scanning loads was studied. The mobility, deformability, and volume change of the nano-objects during the high load scanning were investigated. At last, the force spectroscopy measurement was implemented. Due to the existence of the three-phase contact lines on both tip-NB and tip-ND interactions, force-distance curves exhibit the similar behaviors on both NBs and NDs. However, quantitative analysis shows that the extracted parameters from force-distance curves can be used to distinguish one from the other. This study developed a systematic way to distinguish surface NBs from others nano-objects, which is crucial for surface nanobubble community.