Atomic Force Microscopy Measurement of Slip on Smooth Hydrophobic Surfaces and Possible Artifacts

Slip on hydrophilic and hydrophobic surfaces has been widely studied. Previous studies show a wide range of disagreement over the slip on the smooth hydrophobic surfaces. We have studied the slip on smooth hydrophilic silicon dioxide and hydrophobic octadecyltrichlorosilane (OTS) surfaces immersed in deionized (DI) water and electrolytic solution, using colloid probe atomic force microscopy (CP-AFM). Results suggested a no-slip condition on hydrophilic as well as on hydrophobic surfaces. It was also found that the presence of unknown contaminants causes large uncertainty in the measured slip. Furthermore, we used rectangular as well as V-shaped colloidal probes to study the effect of the shape of AFM cantilever on slip. Results suggested that the shape of colloidal probe does not have an obvious effect on the measured slip lengths.