Non-axisymmetric elastohydrodynamic solid-liquid-solid dewetting: Experiments and numerical modelling

Abstract

Abstract. We have studied the dewetting dynamics of partially wetting liquid films confined between a soft elastic hemisphere and an elastomer layer by means of systematic experiments. We focused on the experimentally most relevant case of non-axisymmetric dewetting, which initiated at the locations of minimum film thickness near the perimeter of the contact area. We found the contact line speed to be highly anisotropic in this case. It is significantly faster in the azimuthal direction along the perimeter of the contact spot than in the radially inwards direction. We developed a three-dimensional, fully coupled numerical model that reproduces many features observed in the experiments. Graphical abstract

Elastohydrodynamic Dewetting of Thin Liquid Films: Elucidating Underwater Adhesion of Topographically Patterned Surfaces

“…Since the liquid is partially wetting, the liquid film becomes unstable and dewets below a minimum film thickness determined by the disjoining pressure. 39 , 46 − 48 The dewetted area grows over time, pushing further liquid out of the contact spot [ Figure 1 d]. Depending on the pillar array period, dewetted areas with very different morphologies were observed during dewetting.…”

“…For a large pillar spacing, the dewetting dynamics is similar to that of a flat surface. 39 , 46 , 47 Figure 4 a shows the anisotropic growth of a dewetted area for pillar spacing d p = 21 μm and a very soft polymer Y = 11.28 kPa. The non-circular shape of the dewetted area is caused by an anisotropy of the time-averaged contact line speed.…”

“…Only Eq. (16) in ref ( 39 ) requires modification to account for the non-flat topography: the function z d ( r⃗ ) is replaced by where the summation is over all micropillars in the array with corresponding center positions r⃗ i . The function describes the axisymmetric shape of a single pillar, where s p = 2.5 μm is the radial distance over which z p changes smoothly from h p to 0 and f hs is the smoothed Heaviside function, defined by Eq.…”

Escape dynamics of liquid droplets confined between soft interfaces: non-inertial coalescence cascades

“…We used the same fully-coupled, threedimensional numerical model that is described in detail in ref. 28. We combine the stationary Cauchy momentum equation for soft, linear elastic materials with the Reynolds equation for thin film flow and apply a disjoining pressure formalism to implement the partial wettability.…”

“…Details of the setup, the experimental procedures as well as the liquid and solid material properties are provided in ref. 28. Fig.…”