Near-field acousto monitoring shear interactions inside a drop of fluid: The role of the zero-slip condition

作者：Wang Xiaohua; Fernandez Rodolfo; Li Nan; Hung Hsien Chih; Venkataraman Anuradha; Nordstrom Richard; La Rosa Andres H^*

来源：Physics of Fluids, 2016, 28(5): 052001.

DOI：10.1063/1.4947597

A full understanding of nanometer-range (near-field) interactions between two sliding solid boundaries, with a mesoscopic fluid layer sandwiched in between, remains challenging. In particular, the origin of the blue-shift resonance frequency experienced by a laterally oscillating probe when approaching a substrate is still a matter of controversy. A simpler problem is addressed here, where a laterally oscillating solid probe interacts with a more sizable drop of fluid that rests on a substrate, aiming at identifying interaction mechanisms that could also be present in the near-field interaction case. It is found that the inelastic component of the probe-fluid interaction does not constitute the main energy-dissipation channel and has a weak dependence on fluid's viscosity, which is attributed to the zero-slip hydrodynamic condition. In contrast, the acoustic signal engendered by the fluid has a stronger dependence on the fluid's viscosity (attributed also to the zero-slip hydrodynamic condition) and correlates well with the probe's resonance frequency red-shift. We propose a similar mechanism happens in near field experiments, but a blue-shift in the probe's resonance results as a consequence of the fluid molecules (subjected to the zero-slip condition at both the probe and substrate boundaries) exerting instead a spring type restoring force on the probe. Published by AIP Publishing.

• 出版日期2016-5