Paper BM-TuP3
Measurement of the Slip Length of Water Flow on Hydrophilic, Hydrophobic and Superhydrophobic Surfaces

Tuesday, October 21, 2008, 6:30 pm, Room Hall D

The growing interest of boundary slip at liquid-solid interface in micro/nano scale is an important issue in microfluidics systems, where lower liquid flow friction is generally desirable. Recent studies have shown that the no-slip boundary condition is not always valid on micro/nano scale, especially on hydrophobic. Theoretical and experimental studies suggest that at the liquid-solid interface, the presence of gas bubbles is responsible for the breakdown of the no-slip condition for hydrophobic surfaces. The degree of boundary slip at liquid-solid interfaces is usually quantified by a parameter called slip length, which infers a distance between a liquid-solid interface and a virtual no-slip interface. Atomic force microscopy is a powerful tool to measure slip length. It has also been used to image nanobubbles in tapping mode. Although the slip length has been reported on both hydrophilic and hydrophobic surfaces, the direct experiment evidence has not been given between nanobubble and apparent slip on hydrophobic surfaces, as well as the relationship between bubbles’ properties and slip length. In this study, the colloidal probe techniques is used to measure hydrodynamic force on hydrophilic, hydrophobic and superhydrophobic surfaces with AFM. The slip length is obtained based on a model proposed in the literature. By combining nanobubble images on hydrophobic and superphdrophobic surfaces, the contribution of nanobubbles to boundary slip is studied with known bubble properties, such as size and distribution density. A model is presented for nanobubbles’ friction reducing mechanisms.