Dresden 2009 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 38: POSTERS Micro- and Nanofluidics
CPP 38.9: Poster
Donnerstag, 26. März 2009, 17:00–19:30, P3
Polystyrene nanodroplets on rubber elastic substrates — •Konstantina Kostourou1, Stephan Herminghaus1, and Ralf Seemann1,2 — 1Max Planck Institute for Dynamics and Self-Organization, D-37073 Göttingen, Germany — 2Experimental Physics, Saarland University, D-66041 Saarbrücken, Germany
We study the shape of polystyrene (PS) nanodroplets on substrates of cross-linked Polydimethylsiloxane (PDMS). These drops deform the rubber elastic substrate onto which they are seated. The three phase contact line is lifted upwards by the interfacial energies, whereas the interface between the drop and the substrate is pushed downwards due to the Laplace pressure of the droplet. The upward deformation of the PDMS is measured by imaging the sessile droplets by atomic force microscopy (AFM) and its exact position is determined by overlapping the topography and the phase signal ("top side"). To measure the downward deformation of the PDMS we lift off the PS droplet from the substrate and image the deformation that is frozen into the "bottom side" of the droplet. By analyzing the profiles of the bottom side of the droplet and assuming that our system can be defined by the Hertzian model for a rigid sphere in contact with a soft elastic plane, we can calculate quantitatively the Elastic Modulus of the substrate, that is in very good agreement with values extracted by other independent techniques (rheology, nanoindentation). Furthermore, the lift-off technique allows us to image the upward displacement of the three phase contact line and to compare it to the results of the deformation in the vicinity of the three phase contact line from the "top side".