固体表面の液滴は長く静止するほど動き出しにくく、速く滑るほど摩擦が減る ―ナノスケールの表面欠陥が生む「摩擦の記憶効果」を解明―

2026-11-10 東京大学

ナノスケールの表面欠陥による接触線のエイジングが生み出す液滴摩擦の履歴効果。拡大図は、静止時間とともに強まる接触線のピン止めを示す。

＜関連情報＞

• https://www.t.u-tokyo.ac.jp/press/pr2026-11-10-001
• https://www.pnas.org/doi/10.1073/pnas.2619504123

接触線の経年変化によって引き起こされる履歴依存的な液滴摩擦 History-dependent droplet friction driven by contact-line aging

Yuanzhe Li, Yaerim Lee, Kaito Hayashi, +7 , and Junichiro Shiomi
Proceedings of the National Academy of Sciences  Published:November 9, 2026
DOI:https://doi.org/10.1073/pnas.2619504123

Abstract

The motion of liquid droplets on solid surfaces is commonly described by contact-line friction, which is generally assumed to increase monotonically with instantaneous velocity. However, such a velocity-only description cannot explain why static droplet friction can exceed dynamic friction or why contact-line friction can become velocity-weakening. Here, we demonstrate that contact-line friction depends jointly on sliding velocity and contact history. Using self-assembled alkylsilane monolayers as molecularly tunable substrates and ionic liquids as low-volatility model liquids, we observe pronounced history-dependent strengthening of contact-line friction on solid-like monolayers, manifested as time-enhanced static friction and velocity-weakening dynamic friction. Both effects are progressively suppressed as the surface is tuned toward a more liquid-like state with a lower density of pinning defects, either by reducing the monolayer chain length or by increasing temperature. We attribute this behavior to nanoscopic contact-line aging, whereby contact-line segments thermally fluctuate and progressively occupy interfacial defects, leading to a progressive increase in contact-line pinning. An aging-based model quantitatively captures the history-dependent onset friction and the low-velocity friction dynamics in our system, while similar logarithmic strengthening across diverse liquid–substrate systems suggests broader applicability of the constitutive framework. These findings establish the coupled effects of contact history and sliding velocity on contact-line friction, extending dynamic wetting beyond velocity-only descriptions and providing a physical basis for controlling macroscopic droplet transport through nanoscale interfacial design.