AFM characterization of nanobubble formation and slip condition in oxygenated and electrokinetically altered fluids

[Display omitted] ► Gas-filled bubbles with nanosize dimensions were observed on hydrophobic surfaces with an AFM. ► The instability to image nanobubbles can be attributed to the surface charge and low roughness of OTS surface. ► Applying negative ions with the anti-static gun reduce the diameter of the nanobubbles in DI water on PS surface. ► The electrons are captured by the water molecules while the oxygen molecules are released to the air. ► Applied electric field to the PS surface, increased the size of nanobubbles while the total count decreased. Nanobubbles are gas-filled features that spontaneously form at the interface of hydrophobic surfaces and aqueous solutions. In this study, an atomic force microscope (AFM) was used to characterize the morphology of nanobubbles formed on hydrophobic polystyrene (PS) and octadecyltrichlorosilane (OTS) films immersed in DI water, saline, saline with oxygen and an electrokinetically altered saline solution produced with Taylor–Couette–Poiseuille flow under elevated oxygen pressure. AFM force spectroscopy was used to evaluate hydrodynamic and electrostatic forces and boundary slip condition in various fluids. The effect of solution, electric field and surface charge on shape, size and density of nanobubbles as well as slip length was quantified and the results and underlying mechanisms are presented in this paper.