Nanoindents produced by nanobubbles on ultrathin polystyrene films in water

Nanobubbles are produced on hydrophobic surfaces when they are immersed in aqueous solutions. The effect of nanobubbles on the immersed surface is of interest in many applications. In the study presented here, immersion of the polystyrene film in de-ionized water for several hours produces nanoindents on the film surface. The typical diameter of the nanoindents is around 20 nm, and the density is about 2.0 x 10(8) mm(-2). The location and formation of nanoindents show strong correlation with the size and location of nanobubbles. A mechanism of nanobubble-induced formation of nanoindents is proposed. The influences of film thickness and nanobubble size on the nanoindents are also discussed.