Regensburg 2016 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 28: Poster - Complex Fluids, Granular Matter, Glasses

DY 28.2: Poster

Dienstag, 8. März 2016, 18:15–21:00, Poster C

Thin film model of drops on soft substrates — •Johannes Kemper and Uwe Thiele — Institut für Theoretische Physik, Westfälische Wilhelms-Universität, Wilhelm-Klemm-Str. 9, 48149 Münster

For drops of liquid on a rigid substrate the force balance that gives the contact angle at the three phase contact line is given by the Young condition that only captures forces parallel to the substrate. However, for liquid drops on viscous soft substrates the balance is given by the Neumann condition that has a vertical and a horizontal component. For a soft substrate with elastic properties, elastic stresses (in general, non-local) have to be accounted for. Here, we present a local approximation of elastic influences that can be incorporated in a long-wave evolution equation for thin viscoelastic films and small-contact angle drops when written in gradient dynamics form. First we use the static limit of the model to determine drop profiles and analyse how the equilibrium contact angles depend on the softness of the substrate. Ridge profiles and radially symmetric drops are analysed employing numerical continuation techniques. It is shown that the simplified model reproduces experimentally observed phenomena like the formation of a wedge-shaped protrusion that is drawn out of the elastic substrate at the contact line [1]. Moreover, the dependence of the contact angle on substrate softness reproduces results of the full elastic model in [2]. These static results give a validity range of parameters for which the elastic long-wave model can be employed in time simulations. [1] T. Kajiya et al., Soft Matter, 9:454-461, 2013; [2] L.A. Lubbers et al., J. Fluid Mech., 747:R1, 2014.