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Séminaire de Jim Yong Jian Wang

Hysteresis of Interfacial Forces near a Moving Contact Line

Hysteresis of Interfacial Forces near a Moving Contact Line

Jim Yong Jian Wang

Laboratoire de Physique Statistique Ecole normale supérieure 24 rue Lhomond 75005 PARIS Cedex 5, FRANCE

The contact angle hysteresis (CAH) as a century long scientific topic still draw many attentions nowadays, which is because of not only the fundamental interest to understand wetting and nonwetting phenomena but also the immense practical application in tertiary oil recovery, drag reduction, advanced materials and microfluidics. In this talk, I will present the direct measurements of the dynamic contact angle and its fluctuations on a thin vertical glass fiber with one end glued onto an atomic force microscope (AFM) cantilever. By moving the fiber up and downward through a liquid-air interface, we are able to accurately measure the hysteresis loop of 28 different liquids with varying surface tensions and contact angles. For the first time, we find the universal behavior of the elastic restoring force of the pinned liquid interface and the dynamic capillary force in both the advancing and receding directions. One model is proposed to quantitatively explain the observed scaling laws beyond the single defect model by Joanny and de Gennes.