Soft Imbibition: experiments in 2D geometries*

Soft gels are commonly used to emulate viscoelastic biological substrates. When a drop of liquid wets a soft gel, the contact line deforms the surface of the gel, forming a ridge. Once the contact line has moved, the recovery depends on the gel rheology and system geometry. Here, we investigate experimentally the imbibition of a wetting fluid in 2D geometries coated with a thin layer of soft gel. When the gel-coated substrate is placed in contact with a fluid reservoir, the liquid spontaneously invades the channel. During the experiment, the thickness of the gel coating is constant, away from the contact line. We measure the imbibition length and compare its time dependence with the classical ''diffusive'' response observed in uniform channels and porous media with rigid walls. We show that the imbibition dynamics depend on the fluid and gel-layer properties. The results demonstrate that soft materials modify wetting dynamics and could lead to the development of soft coating to control transport.