Wed October 26th 2016
16:00 – 17:00
ZH286
Seminar Interfacial nanobububbles and their implication for boundary slip in micro/nanofluidics
Yuliang Wang

Details:

Nonslip boundary condition at solid-liquid interfaces has been at the center of fluidics for centuries and is generally used to resolve the Navier-Stokes equations. In the nonslip boundary condition, it is assumed that the relative velocity between a solid wall and liquid flow is zero at the solid-liquid interfaces. However, numerous studies have shown that on hydrophobic/superhydrophobic surfaces the fluid velocity near the solid surface is not equal to the velocity of the solid surface, a phenomenon called boundary slip. Theoretical and experimental studies suggest that the presence of nanobubbles at solid-liquid interfaces is responsible for the boundary slip. During wetting of a hydrophobic surface with an aqueous solution, spherical cap nanobubbles with dimensions of 5–100 nm in height and 50–800 nm in diameter can be produced. The existence of the nanobubbles has been proved by many technologies, including atomic force microscope (AFM), rapid cryofixation/freeze fracture, and X-ray reflectivity measurements.
In this talk, experimental studies of nanobubbles and their implication for boundary slips will be presented. In the study of nanobubbles, nanobubble characterization, AFM tip-nanobubble interaction and nanobubble - sample substrate interaction are presented. The mechanism of nanobubbles induced nanoindents is revealed and the concept of nanobubble immobility and is proposed. In the study of boundary slips, we focus on the research performed using contact and tapping mode atomic force microscopy methods to study boundary slip on hydrophilic, hydrophobic, and superhydrophobic surfaces. The impact of surface roughness and hydrophobicity on measured slip length is discussed. The process of how to eliminate the influences of cantilever deflection and electrostatic forces on experimental measurement is discussed. Based on nanobubble imaging on a hydrophobic surface, the correlation of nanobubbles on boundary slip is investigated on various hydrophobic surfaces.
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