Analysis of the filling behaviour of trenches via air bubble tracking

Imprint of thin PDMS layers with undercut trenches features a behaviour different from the one known from binary structures. In order to compare the filling behaviour of such geometries a moulding process with preheated masters was performed. Due to the temperature accelerated curing of the reactive mixture this method enabled the identification of different filling states by ‘freezing’ of an incomplete filling situation. The different filling states could be discerned by means of the final location of the ‘frozen’ air bubbles and the filling length of the trenches. It turned out that, in contrast to the behaviour of binary trenches, the filling of undercut trenches proceeds primarily in lateral direction along the trench. This behaviour could be understood by pinning of the contact line between liquid and solid at outer edges.