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Can Polymers Slide ? New Insights from Capillary-Driven Flows in Thin Films
The motion of small amounts of liquid on the micro- and nanoscale is of enormous
scientific interest and additionally holds great technological potential, e.g. in lab-on-a-chip
applications for pharmaceuticals, biological analysis or chemical reactions. When
downsizing devices, interfacial and confinement effects become important. Although we
know from Poiseulle flow that the no-slip boundary condition holds for many macroscopic
flows, it can fail on smaller length scales. In this presentation, slip effects will be addressed
for different thin film geometries, starting with dewetting polymer films. If a thin liquid film
supported by a solid substrate is not stable, distinct flow mechanisms can be observed :
spinodal dewetting and dewetting by nucleation of holes. The morphological and temporal
evolution of holes gives information about the slip boundary condition [1]. Moreover, the
late stage of the dewetting process features a Rayleigh-Plateau-type instability, whose
rise-time and morphology are also governed by interfacial slip. Recently, we turned to
polymer films that exhibit a small step on their surface. Mediated by the viscosity, Laplace
pressure drives a flow resulting in the levelling of the step [2]. Based on hydrodynamic thin
film models for capillary-driven flows, both systems, dewetting and stepped films, elucidate
nanoscale polymer rheology, open new perspectives for a quantification of the
hydrodynamic boundary condition at the solid/liquid interface, and provide insights into
polymer properties at interfaces on the molecular level.
[1] O. Bäumchen, R. Fetzer, and K. Jacobs, Physical Review Letters 103, 247801 (2009).
[2] J.D. McGraw, T. Salez, O.Bäumchen, E. Raphael, and K. Dalnoki-Veress, Physical
Review Letters 109, 128303 (2012).
Séminaire du laboratoire Gulliver