Study of nanobubbles on hydrophilic and hydrophobic alumina surfaces

Recent studies have shown that a high attractive force acts between poorly wettable surfaces, which cannot be explained by the conventional DLVO-theory. This hydrophobic force is caused by very small bridging bubbles. Such forces can improve the efficiency in deep bed filtration applications using hydrophobized filter materials. An atomic force microscope was used for the characterization of nanobubbles by investigating hydrophilic and hydrophobic Al2O3-substrates in water at 10, 20 and 30 degrees C. The nanobubbles were therefore imaged via intermittent mode AFM. Height and diameter distributions were represented as well as calculated microscopic contact angles for bubbles of various sizes. The results were compared with force measurements and the potential differences were discussed. Furthermore, the stability of nanobubbles on smooth and rough alumina surfaces with an increasing scan force was presented. (C) 2016 Elsevier B.V. All rights reserved.