Properties of blisters formed on polymer film and differences from surface nanobubbles.

When studying surface nanobubbles on film coated substrates, a kind of bubble-like domain called blisters are probably forming at the solid-liquid interface together with nanobubbles. This may easily lead to misunderstanding of the characteristics and applications of surface nanobubbles and thus continue to cause problems within the nanobubble community. Therefore, how to distinguish surface nanobubbles from blisters is a problem. Herein, the morphology and properties of blisters are investigated on both smooth and nanopitted polystyrene (PS) film in degassed water. The morphology and contact angle of blisters are similar to that of surface nanobubbles. However, blisters were observed to be punctured under the tip-blister interaction and be torn broken by atomic force microscope (AFM) tip in the process of scanning. At the same time, nanopits on the surface of blisters that formed on pitted PS film can be seen clearly. These provide direct and visual evidence for distinguishing blisters from surface nanobubbles. In addition, surface nanobubbles and blisters on smooth and pitted PS film in air-equilibrated water are studied. No punctured surface nanobubble was observed, and the force curves obtained on surface nanobubbles as well as the change in height of blisters and surface nanobubbles under large scanning force show that surface nanobubbles are much softer than blisters.