Mathieu Lizée – Hint of phononic friction in the slippage supercooled glycerol on mica

Mathieu Lizée, Laboratoire de physique – ENS

 

 

The fundamental understanding of friction of liquids on solid surfaces remains one of the key knowledge gaps in the transport of fluids. While the standard perspective emphasizes the role of wettability and commensurability, recent works have unveiled the crucial role of the solid’s internal excitations, whether electronic or phononic, on liquid-solid dissipation. In this work, we take advantage of the considerable variation of the molecular timescales of supercooled glycerol under mild change of temperature, in order to explore how friction depends on the liquid’s molecular dynamics. Using a dedicated tuning-fork-based AFM to measure the hydrodynamic slippage of glycerol on mica, we report a 2-order of magnitude increase of the slip length with decreasing temperature by only 30◦C. However the solid-liquid friction coefficient is found to be a non monotonous function of the fluid molecular relaxation rate, fα, at odd with an expected Arrhenius activated behavior. In particular we report a linear increase of friction with glycerol’s molecular relaxation rate at high temperature, which cannot be accounted for by existing models which treat the solid surface as a static corrugated potential. We show that this unconventional scaling of friction can be explained by a contribution of the solid’s vibrations which resonate with high frequency density fluctuations in the liquid. Such a resonance allows efficient momentum transfer and boosts friction. This dynamical contribution to friction relies on the overlap of the phononic structure of mica with the vibrational modes of the liquid. As a consequence, it opens new perspectives to control hydrodynamic flows by properly engineering phononic excitation spectra in channel walls and industrially relevant membrane materials.