Experimental study of nanobubbles and nanodroplets on hydrophobic/hydrophillic combined surfaces

Abstract

The effects of surface wettability on nanobubbles and nanodroplets at the solid/liquid and solid/vapor interfaces are studied by using atomic force microscopy (AFM) and environmental scanning electron microscopy (ESEM). Nanobubbles generated by the solvent exchange method appear preferentially on the hydrophobic surface but hydrophilic surface is found to enhance their generation and stability. The interfacial nanobubbles are confirmed to be of spherical-capped shape but the tapping of AFM probe can deform them and the deformed nanobubbles are pretty stable even though two are collapsed into a butterfly shape. Nanodroplets are generated by condensation of water vapor in ESEM. Both the nanodroplets and nanobubbles are of more flattened shape than the macroscopic ones. Micro/nanoscale fabrication techniques of hydrophobic/ hydrophilic combined surface are also discussed.