Wed February 13th 2013
16:00
ZH286
Seminar Some strange phenomena observed in the wetting of gels, and their possible interpretation in terms of elastowetting
Laurent Limat

Details:

We have investigated the wetting properties of soft polymer gels by observing or inflating sessile drops deposed on the free surface of the gel, in two limit situations: a gel absorbing also the liquid (swelling phenomena), while being distorted by the liquid surface tension, and a viscoelastic gel having zero absorption. In the first case, a transient partial wetting situation with high hysteresis, is observed at short times, followed by a recession of a drop under total wetting after a finite time similar to what is observed for sessile drops evaporating in air. In the second case, a drop inflated progressively on the gel displays complex behaviors of stick-slip ruled by the typical frequency built upon mean contact line velocity and drop size. We show that there are two transitions leading to stick slip, one at high frequency and the other at low frequency, both seeming to arise from the impossibility to satisfy at the same time in the rheological response of the solid and liquid component of the gel. Finaly I compare these results to a modification of Shanahan's approach of elstowetting including surface tension of the substrate. The stick-slip seems to involve jumps of the contact line when this one reaches the advancing contact angle on the inclined side of the ridge formed by liquid surface tension around the drop, its usual logarithmic profile being cut at a typical scale of order of the elastocapillary length. This cut-off is consistent with recent works in Yale, Twente and ESPCI , on one hand, and with arguments developed long ago by Extrand and Kumagai for elastomers, on the other.
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The 10th Complex Motion in Fluids 2021
AQUA
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