Julien Dervaux (Laboratoire Matière et Systèmes Complexes, Université de Paris-Diderot). Contact lines on soft solids.

Elastocapillarity describes the deformations of soft materials by surface tensions and is involved in a broad range of applications, from micro-electromechanical devices to cell patterning on soft surfaces. Within the very rich field of elastocapillarity, studies on the wetting of soft materials by sessile or moving droplets, so-called elastowetting phenomena, are presently attracting great interest. In contrast with the wetting of liquids on rigid materials, the liquid surface tension at the contact line of a drop deforms the substrate and leads to the formation of a “ridge”, which in turn affects drastically the static and dynamic wetting properties.

In this talk, I will briefly introduce the linear theory of static elastowetting before presenting experimental and theoretical results beyond this static linear approximation.

First I will show how the viscous dissipation in soft solids controls the velocity of moving contact lines and how this dissipation can be tuned to control the motion of droplets on thin films. Then, I will present results on the relaxation of a ridge following the removal of a drop. The observed logarithmic decrease of the ridge at long timescales is well captured by a poroelastic model which also explains quantitatively the existence of long-lived “footprints” left by drops on gels and elastomers, as reported in ancient works in the field of elastowetting. Finally I will discuss nonlinear effects in elastowetting and present recent numerical simulations that might shed light on the controversial Shuttleworth effect.