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Abstract:
In the present work, we study the wetting and dewetting phenomena on viscoelastic substrates, which are either planar or topographically structured.The main focus has been given primarily to the planar substrates, where the dewetting behaviour of thin polystyrene (PS) .films on viscoleastic substrates (cross-linked Polydimethylsiloxane - PDMS and molten Polymethylmethacrylate - PMMA) is explored.Our aim is to study how the viscoelastic properties of the substrate a ffect the dewetting dynamics as well as the equilibrium state of the overlying polymer thin .film and to gain knowledge on the mechanisms that dominate the dewetting process.Thus, we have determined the behaviour of the dewetting velocity as a function of time and as a function of the substrate"s viscoelastic properties. The experimental results in both cases are in good agreement with previous theoretical predictions.In particular, we are interested in the overall shape of the rim surrounding the growing hole, i.e. both the air/PS and PS/substrate interface. We demonstrate that the shape of the substrate deformation below the liquid rim changes dramatically depending on whether the substrate"s elastic or viscous properties dominate.Additionally, we study the shape of sessile PS droplets in equilibrium on the substrate. We are interested in the full shape of the droplet, i.e. the shape of the air/PS interface, the deformation at the dry side of the three phase contact line (TPCL) and the deformation below the droplet.Finally, a preliminary study has been conducted regarding the wetting phenomena in rectangular grooves of PDMS and how these depend on the substrate wettability and geometry. Tuning independently these two parameters, the wetting dynamics is tailored accordingly, resulting in a different .final order of the liquid morphologies.
